Merge branch 'feature/banEvasion'

common/src/main/java/eu/mhsl/craftattack/spawn/common/appliances/tooling/loginLog/LoginAttempt.java

@@ -0,0 +1,32 @@
+package eu.mhsl.craftattack.spawn.common.appliances.tooling.loginLog;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.net.InetAddress;
+import java.time.Instant;
+import java.util.UUID;
+
+record LoginAttempt(
+    @NotNull Instant at,
+    @NotNull UUID uuid,
+    @NotNull String name,
+    @NotNull String ip,
+    boolean bedrock,
+    @NotNull String stage,
+    @NotNull String result,
+    @Nullable String reason
+) {
+    static final String STAGE_PRE_LOGIN = "PRE_LOGIN";
+    static final String STAGE_LOGIN = "LOGIN";
+    static final String STAGE_WEBSITE = "WEBSITE";
+    static final String RESULT_ABORTED = "ABORTED";
+
+    static String ipOf(@Nullable InetAddress address) {
+        return address == null ? "unknown" : address.getHostAddress();
+    }
+
+    LoginAttempt withOutcome(@NotNull String stage, @NotNull String result, @Nullable String reason) {
+        return new LoginAttempt(this.at, this.uuid, this.name, this.ip, this.bedrock, stage, result, reason);
+    }
+}

common/src/main/java/eu/mhsl/craftattack/spawn/common/appliances/tooling/loginLog/LoginLog.java

@@ -0,0 +1,196 @@
+package eu.mhsl.craftattack.spawn.common.appliances.tooling.loginLog;
+
+import com.google.common.net.InetAddresses;
+import eu.mhsl.craftattack.spawn.core.Main;
+import eu.mhsl.craftattack.spawn.core.api.server.HttpServer;
+import eu.mhsl.craftattack.spawn.core.appliance.Appliance;
+import eu.mhsl.craftattack.spawn.core.database.Database;
+import eu.mhsl.craftattack.spawn.core.event.LoginAttemptRecordedEvent;
+import eu.mhsl.craftattack.spawn.core.event.SpawnEvent;
+import eu.mhsl.craftattack.spawn.core.util.network.Networks;
+import eu.mhsl.craftattack.spawn.core.util.server.Floodgate;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.serializer.plain.PlainTextComponentSerializer;
+import org.bukkit.Bukkit;
+import org.bukkit.event.Listener;
+import org.bukkit.scheduler.BukkitTask;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.net.InetAddress;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.Statement;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.ZoneOffset;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * Records every login attempt (allowed or not) with its IP address in the table login_attempts
+ * (schema: resources/migrations/loginLog). Basis for detecting ban evasion.
+ * After each insert a LoginAttemptRecordedEvent is fired on the database thread.
+ * The website reports signups and logins of its users via POST /api/loginlog/website.
+ * Never blocks or delays a login: writes run on the database thread, failures are only logged.
+ */
+public class LoginLog extends Appliance {
+    private static final int MAX_REASON_LENGTH = 255;
+    private static final Duration PENDING_TIMEOUT = Duration.ofSeconds(60);
+    private static final long TICKS_PER_MINUTE = 20L * 60;
+
+    private final Map<UUID, LoginAttempt> pendingAttempts = new ConcurrentHashMap<>();
+    private final List<BukkitTask> tasks = new ArrayList<>();
+    private Database database;
+    private int retentionMonths;
+
+    public LoginLog() {
+        super("loginLog");
+    }
+
+    @Override
+    public void onEnable() {
+        this.database = Main.instance().getDatabase();
+        if(!this.database.isAvailable()) {
+            Main.logger().warning("LoginLog: no database configured, login attempts are not recorded");
+            return;
+        }
+        this.retentionMonths = this.localConfig().getInt("retentionMonths", 16);
+
+        this.tasks.add(Bukkit.getScheduler().runTaskTimerAsynchronously(
+            Main.instance(), this::flushStaleAttempts, TICKS_PER_MINUTE, TICKS_PER_MINUTE
+        ));
+        this.tasks.add(Bukkit.getScheduler().runTaskTimerAsynchronously(
+            Main.instance(), this::deleteExpired, TICKS_PER_MINUTE, TICKS_PER_MINUTE * 60 * 24
+        ));
+    }
+
+    @Override
+    public void onDisable() {
+        this.tasks.forEach(BukkitTask::cancel);
+    }
+
+    void onPreLogin(UUID uuid, String name, @Nullable InetAddress address, String result, @Nullable Component kickMessage) {
+        if(!this.database.isAvailable()) return;
+        LoginAttempt attempt = new LoginAttempt(
+            Instant.now(), uuid, name, LoginAttempt.ipOf(address), Floodgate.isFloodgateUuid(uuid),
+            LoginAttempt.STAGE_PRE_LOGIN, result, plainText(kickMessage)
+        );
+
+        // allowed attempts are written after the login event, so they carry the final result
+        if(kickMessage == null) this.pendingAttempts.put(uuid, attempt);
+        else this.write(attempt);
+    }
+
+    void onLogin(UUID uuid, String name, @Nullable InetAddress address, String result, @Nullable Component kickMessage) {
+        if(!this.database.isAvailable()) return;
+        LoginAttempt pending = this.pendingAttempts.remove(uuid);
+        LoginAttempt attempt = pending != null
+            ? pending
+            : new LoginAttempt(Instant.now(), uuid, name, LoginAttempt.ipOf(address), Floodgate.isFloodgateUuid(uuid), "", "", null);
+
+        this.write(attempt.withOutcome(LoginAttempt.STAGE_LOGIN, result, plainText(kickMessage)));
+    }
+
+    private void flushStaleAttempts() {
+        Instant threshold = Instant.now().minus(PENDING_TIMEOUT);
+        this.pendingAttempts.values().removeIf(attempt -> {
+            if(attempt.at().isAfter(threshold)) return false;
+            this.write(attempt.withOutcome(LoginAttempt.STAGE_PRE_LOGIN, LoginAttempt.RESULT_ABORTED, null));
+            return true;
+        });
+    }
+
+    private void write(LoginAttempt attempt) {
+        String network = Networks.networkOf(attempt.ip());
+        String sql = "INSERT INTO login_attempts (at, uuid, name, ip, network, bedrock, stage, result, reason) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)";
+        this.database.execute("recording login attempt of " + attempt.name(), connection -> {
+            long id;
+            try(PreparedStatement statement = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
+                statement.setObject(1, LocalDateTime.ofInstant(attempt.at(), ZoneOffset.UTC));
+                statement.setString(2, attempt.uuid().toString());
+                statement.setString(3, attempt.name());
+                statement.setString(4, attempt.ip());
+                statement.setString(5, network);
+                statement.setBoolean(6, attempt.bedrock());
+                statement.setString(7, attempt.stage());
+                statement.setString(8, attempt.result());
+                statement.setString(9, attempt.reason());
+                statement.executeUpdate();
+                try(ResultSet keys = statement.getGeneratedKeys()) {
+                    if(!keys.next()) return;
+                    id = keys.getLong(1);
+                }
+            }
+            SpawnEvent.call(new LoginAttemptRecordedEvent(new LoginAttemptRecordedEvent.RecordedAttempt(
+                id, attempt.at(), attempt.uuid(), attempt.name(), network, attempt.stage(), attempt.result()
+            )));
+        });
+    }
+
+    private void deleteExpired() {
+        String sql = "DELETE FROM login_attempts WHERE at < UTC_TIMESTAMP() - INTERVAL ? MONTH";
+        this.database.execute("deleting expired login attempts", connection -> {
+            try(PreparedStatement statement = connection.prepareStatement(sql)) {
+                statement.setInt(1, this.retentionMonths);
+                int deleted = statement.executeUpdate();
+                if(deleted > 0) Main.logger().info(String.format("LoginLog: deleted %d expired login attempts", deleted));
+            }
+        });
+    }
+
+    private record WebsiteEvent(String event, String uuid, String username, String ip) {
+    }
+
+    private void recordWebsiteEvent(WebsiteEvent request) {
+        if(request == null) throw new IllegalArgumentException("Request body missing");
+        if(!this.database.isAvailable()) throw new IllegalStateException("No database configured");
+
+        String event = request.event() == null ? "" : request.event().trim().toUpperCase(Locale.ROOT);
+        if(!event.equals("SIGNUP") && !event.equals("LOGIN"))
+            throw new IllegalArgumentException("Field 'event' must be 'signup' or 'login'");
+        if(request.uuid() == null || request.uuid().isBlank())
+            throw new IllegalArgumentException("Field 'uuid' is required");
+        UUID uuid;
+        try {
+            uuid = UUID.fromString(request.uuid().trim());
+        } catch(IllegalArgumentException e) {
+            throw new IllegalArgumentException("Field 'uuid' is not a valid UUID");
+        }
+        if(request.username() == null || request.username().isBlank())
+            throw new IllegalArgumentException("Field 'username' is required");
+        if(request.ip() == null || !InetAddresses.isInetAddress(request.ip().trim()))
+            throw new IllegalArgumentException("Field 'ip' is not a valid IP address");
+
+        this.write(new LoginAttempt(
+            Instant.now(), uuid, request.username().trim(), request.ip().trim(), Floodgate.isFloodgateUuid(uuid),
+            LoginAttempt.STAGE_WEBSITE, event, null
+        ));
+    }
+
+    @Override
+    public void httpApi(HttpServer.ApiBuilder apiBuilder) {
+        apiBuilder.post("website", WebsiteEvent.class, (request, original) -> {
+            this.recordWebsiteEvent(request);
+            return HttpServer.nothing;
+        });
+    }
+
+    private static @Nullable String plainText(@Nullable Component component) {
+        if(component == null) return null;
+        String text = PlainTextComponentSerializer.plainText().serialize(component)
+            .strip()
+            .replaceAll("\\s*\\n\\s*", " | ");
+        return text.length() > MAX_REASON_LENGTH ? text.substring(0, MAX_REASON_LENGTH) : text;
+    }
+
+    @Override
+    protected @NotNull List<Listener> listeners() {
+        return List.of(new LoginLogListener());
+    }
+}

common/src/main/java/eu/mhsl/craftattack/spawn/common/appliances/tooling/loginLog/LoginLogListener.java

@@ -0,0 +1,34 @@
+package eu.mhsl.craftattack.spawn.common.appliances.tooling.loginLog;
+
+import eu.mhsl.craftattack.spawn.core.appliance.ApplianceListener;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.player.AsyncPlayerPreLoginEvent;
+import org.bukkit.event.player.PlayerLoginEvent;
+
+/**
+ * Listens on MONITOR priority, so the final result of all other checks (whitelist, bans, maintenance, ...) is recorded.
+ */
+class LoginLogListener extends ApplianceListener<LoginLog> {
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onPreLogin(AsyncPlayerPreLoginEvent event) {
+        this.getAppliance().onPreLogin(
+            event.getUniqueId(),
+            event.getName(),
+            event.getAddress(),
+            event.getLoginResult().name(),
+            event.getLoginResult() == AsyncPlayerPreLoginEvent.Result.ALLOWED ? null : event.kickMessage()
+        );
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onLogin(PlayerLoginEvent event) {
+        this.getAppliance().onLogin(
+            event.getPlayer().getUniqueId(),
+            event.getPlayer().getName(),
+            event.getAddress(),
+            event.getResult().name(),
+            event.getResult() == PlayerLoginEvent.Result.ALLOWED ? null : event.kickMessage()
+        );
+    }
+}

common/src/main/resources/migrations/loginLog/001_create_login_attempts.sql

@@ -0,0 +1,15 @@
+-- Every login attempt (allowed or not) with the player's IP, basis for detecting ban evasion.
+CREATE TABLE login_attempts (
+    id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+    at DATETIME(3) NOT NULL COMMENT 'UTC',
+    uuid CHAR(36) NOT NULL,
+    name VARCHAR(64) NOT NULL,
+    ip VARCHAR(45) NOT NULL,
+    bedrock BOOLEAN NOT NULL,
+    stage VARCHAR(16) NOT NULL COMMENT 'PRE_LOGIN or LOGIN',
+    result VARCHAR(32) NOT NULL COMMENT 'Bukkit login result, or ABORTED',
+    reason VARCHAR(255) NULL COMMENT 'kick message as plain text',
+    KEY idx_at (at),
+    KEY idx_uuid (uuid),
+    KEY idx_ip (ip)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

common/src/main/resources/migrations/loginLog/002_add_network.sql

@@ -0,0 +1,6 @@
+-- Connection key per attempt: the IPv4 address or the IPv6 /64 prefix. Groups accounts by internet connection.
+ALTER TABLE login_attempts
+    ADD COLUMN IF NOT EXISTS network VARCHAR(45) NULL COMMENT 'IPv4 address or IPv6 /64 prefix, NULL if unknown' AFTER ip,
+    ADD KEY IF NOT EXISTS idx_network_at (network, at);
+
+UPDATE login_attempts SET network = ip WHERE ip REGEXP '^[0-9]{1,3}([.][0-9]{1,3}){3}$';

common/src/main/resources/migrations/loginLog/003_add_lookup_indexes.sql

@@ -0,0 +1,5 @@
+-- Latest name per account and account per name, used for every name shown in the ban evasion dialogs.
+ALTER TABLE login_attempts
+    ADD KEY IF NOT EXISTS idx_uuid_at (uuid, at),
+    ADD KEY IF NOT EXISTS idx_name_at (name, at),
+    DROP KEY IF EXISTS idx_uuid;

core/src/main/java/eu/mhsl/craftattack/spawn/core/Main.java

@@ -4,6 +4,7 @@ import eu.mhsl.craftattack.spawn.core.api.client.RepositoryLoader;
 import eu.mhsl.craftattack.spawn.core.api.server.HttpServer;
 import eu.mhsl.craftattack.spawn.core.appliance.Appliance;
 import eu.mhsl.craftattack.spawn.core.config.Configuration;
+import eu.mhsl.craftattack.spawn.core.database.Database;
 import org.bukkit.Bukkit;
 import org.bukkit.event.HandlerList;
 import org.bukkit.plugin.java.JavaPlugin;
@@ -23,6 +24,7 @@ public final class Main extends JavaPlugin {
 
     private List<Appliance> appliances;
     private RepositoryLoader repositoryLoader;
+    private Database database;
     private Reflections reflections;
 
     @Override
@@ -42,6 +44,8 @@ public final class Main extends JavaPlugin {
         Configuration.readConfig();
         List<String> disabledAppliances = Configuration.pluginConfig.getStringList("disabledAppliances");
 
+        this.database = new Database(Configuration.cfg.getConfigurationSection("database"));
+
         Main.logger().info("Initializing reflections...");
         this.reflections = new Reflections(projectPackage);
 
@@ -94,6 +98,8 @@ public final class Main extends JavaPlugin {
         HandlerList.unregisterAll(this);
         Bukkit.getScheduler().cancelTasks(this);
         Main.logger().info("Disabled " + this.appliances.size() + " appliances!");
+
+        if(this.database != null) this.database.close();
     }
 
     public Appliance restartAppliance(Class<? extends Appliance> applianceClass) {
@@ -138,6 +144,10 @@ public final class Main extends JavaPlugin {
         return this.appliances;
     }
 
+    public Database getDatabase() {
+        return this.database;
+    }
+
     public RepositoryLoader getRepositoryLoader() {
         return this.repositoryLoader;
     }

core/src/main/java/eu/mhsl/craftattack/spawn/core/api/client/HttpRepository.java

@@ -10,6 +10,7 @@ import java.net.URISyntaxException;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
+import java.time.Duration;
 import java.util.List;
 import java.util.Objects;
 import java.util.function.Consumer;
@@ -74,6 +75,19 @@ public abstract class HttpRepository extends Repository {
         return this.execute(request, outputType, null);
     }
 
+    /**
+     * Like {@link #get(String, Class)}, but the request fails with an exception once the timeout has passed.
+     */
+    protected <TOutput> ReqResp<TOutput> get(String command, Duration timeout, Class<TOutput> outputType) {
+        HttpRequest request = this.getRequestBuilder(this.getUri(command, parameters -> {
+            }))
+            .timeout(timeout)
+            .GET()
+            .build();
+
+        return this.execute(request, outputType, null);
+    }
+
     private URI getUri(String command, Consumer<URIBuilder> parameters) {
         try {
             URIBuilder builder = new URIBuilder(this.basePath + "/" + command);

core/src/main/java/eu/mhsl/craftattack/spawn/core/api/server/HttpServer.java

@@ -79,7 +79,7 @@ public class HttpServer {
             try {
                 response = new Response(Response.Status.SUCCESS, null, exec.get());
             } catch(Exception e) {
-                response = new Response(Response.Status.FAILURE, e, null);
+                response = new Response(Response.Status.FAILURE, e.getMessage(), null);
             }
             return HttpServer.this.gson.toJson(response);
         }

core/src/main/java/eu/mhsl/craftattack/spawn/core/appliance/Appliance.java

@@ -4,6 +4,7 @@ import eu.mhsl.craftattack.spawn.core.Main;
 import eu.mhsl.craftattack.spawn.core.api.client.Repository;
 import eu.mhsl.craftattack.spawn.core.api.server.HttpServer;
 import eu.mhsl.craftattack.spawn.core.config.Configuration;
+import eu.mhsl.craftattack.spawn.core.database.Migrations;
 import org.bukkit.Bukkit;
 import org.bukkit.command.PluginCommand;
 import org.bukkit.configuration.ConfigurationSection;
@@ -107,6 +108,7 @@ public abstract class Appliance {
     }
 
     public void enableSequence(JavaPlugin plugin) {
+        Migrations.apply(Main.instance().getDatabase(), this.migrationsName());
         this.onEnable();
         this.initialize(plugin);
     }
@@ -116,6 +118,14 @@ public abstract class Appliance {
         this.destruct(plugin);
     }
 
+    /**
+     * Name of the folder containing this appliance's SQL migrations: {@code migrations/<name>/} in the resources.
+     */
+    private String migrationsName() {
+        String name = this.getClass().getSimpleName();
+        return Character.toLowerCase(name.charAt(0)) + name.substring(1);
+    }
+
     protected <T extends Appliance> T queryAppliance(Class<T> clazz) {
         return Main.instance().getAppliance(clazz);
     }
@@ -129,6 +139,7 @@ public abstract class Appliance {
             PluginCommand command = this.createPluginCommand(name, plugin);
             command.setExecutor(executor);
             command.setTabCompleter(executor);
+            if(executor.permission() != null) command.setPermission(executor.permission());
             plugin.getServer().getCommandMap().register(plugin.getName(), command);
         } catch(Exception e) {
             throw new RuntimeException(String.format("Failed to register command '%s'", name), e);

core/src/main/java/eu/mhsl/craftattack/spawn/core/appliance/ApplianceCommand.java

@@ -30,6 +30,14 @@ public abstract class ApplianceCommand<T extends Appliance> extends CachedApplia
         this.errorMessage = errorMessage;
     }
 
+    /**
+     * Permission needed to see and run the command. Paper leaves the command out of the command tree
+     * of players without it, so for them it does not exist. Null means everyone.
+     */
+    public @Nullable String permission() {
+        return null;
+    }
+
     @Override
     public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
         try {

core/src/main/java/eu/mhsl/craftattack/spawn/core/database/Database.java

@@ -0,0 +1,145 @@
+package eu.mhsl.craftattack.spawn.core.database;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+import org.bukkit.configuration.ConfigurationSection;
+import org.jetbrains.annotations.Nullable;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.logging.Level;
+
+/**
+ * Shared MariaDB access for all appliances. Configured in the "database" section of the config.
+ * All statements run on a single background thread in submission order, so callers (e.g. login events)
+ * are never blocked. Without configuration the database is unavailable and all calls are ignored.
+ */
+public class Database {
+    @FunctionalInterface
+    public interface SqlAction {
+        void run(Connection connection) throws SQLException;
+    }
+
+    @FunctionalInterface
+    public interface SqlQuery<T> {
+        T run(Connection connection) throws SQLException;
+    }
+
+    private final @Nullable String jdbcUrl;
+    private final String user;
+    private final String password;
+    private final ThreadPoolExecutor executor = new ThreadPoolExecutor(
+        1, 1, 0, TimeUnit.MILLISECONDS,
+        new ArrayBlockingQueue<>(1000),
+        runnable -> new Thread(runnable, "Spawn-Database"),
+        new ThreadPoolExecutor.AbortPolicy()
+    );
+    private @Nullable Connection connection;
+
+    public Database(@Nullable ConfigurationSection config) {
+        String host = config == null ? "" : config.getString("host", "");
+        if(host.isBlank()) {
+            this.jdbcUrl = null;
+            this.user = "";
+            this.password = "";
+            Main.logger().info("No database configured, database features are disabled");
+            return;
+        }
+
+        this.jdbcUrl = String.format(
+            "jdbc:mysql://%s:%d/%s?connectTimeout=3000&socketTimeout=10000&allowMultiQueries=true",
+            host,
+            config.getInt("port", 3306),
+            config.getString("name", "craftattack")
+        );
+        this.user = config.getString("user", "");
+        this.password = config.getString("password", "");
+    }
+
+    public boolean isAvailable() {
+        return this.jdbcUrl != null;
+    }
+
+    /**
+     * Runs the action in the background without waiting for it. Errors are logged.
+     */
+    public void execute(String description, SqlAction action) {
+        if(!this.isAvailable()) return;
+        try {
+            this.executor.execute(() -> {
+                try {
+                    action.run(this.getConnection());
+                } catch(SQLException e) {
+                    this.handleError(description, e);
+                } catch(RuntimeException e) {
+                    Main.logger().log(Level.WARNING, String.format("Database: %s failed", description), e);
+                }
+            });
+        } catch(RejectedExecutionException e) {
+            Main.logger().warning("Database queue full, dropping statement");
+        }
+    }
+
+    /**
+     * Runs the query in the background. The future fails if the database is unavailable or the query fails.
+     */
+    public <T> CompletableFuture<T> query(SqlQuery<T> query) {
+        CompletableFuture<T> future = new CompletableFuture<>();
+        if(!this.isAvailable()) {
+            future.completeExceptionally(new IllegalStateException("No database configured"));
+            return future;
+        }
+        try {
+            this.executor.execute(() -> {
+                try {
+                    future.complete(query.run(this.getConnection()));
+                } catch(SQLException e) {
+                    this.closeConnection();
+                    future.completeExceptionally(e);
+                } catch(RuntimeException e) {
+                    future.completeExceptionally(e);
+                }
+            });
+        } catch(RejectedExecutionException e) {
+            Main.logger().warning("Database queue full, dropping statement");
+            future.completeExceptionally(e);
+        }
+        return future;
+    }
+
+    public void close() {
+        this.executor.shutdown();
+        try {
+            if(!this.executor.awaitTermination(5, TimeUnit.SECONDS))
+                Main.logger().warning("Database: pending statements were not finished before shutdown");
+        } catch(InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+        this.closeConnection();
+    }
+
+    private Connection getConnection() throws SQLException {
+        if(this.connection == null || !this.connection.isValid(2))
+            this.connection = DriverManager.getConnection(this.jdbcUrl, this.user, this.password);
+        return this.connection;
+    }
+
+    private void closeConnection() {
+        if(this.connection == null) return;
+        try {
+            this.connection.close();
+        } catch(SQLException ignored) {
+        }
+        this.connection = null;
+    }
+
+    private void handleError(String description, SQLException e) {
+        Main.logger().log(Level.WARNING, String.format("Database: %s failed: %s", description, e.getMessage()));
+        this.closeConnection();
+    }
+}

core/src/main/java/eu/mhsl/craftattack/spawn/core/database/Migrations.java

@@ -0,0 +1,138 @@
+package eu.mhsl.craftattack.spawn.core.database;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Applies SQL migration files shipped in the plugin jar.
+ * Files live in {@code migrations/<appliance>/NNN_description.sql} and run in ascending order of NNN.
+ * Applied versions are tracked per appliance in the table {@code schema_migrations}.
+ */
+public class Migrations {
+    private static final String DIRECTORY = "migrations/";
+    private static final Pattern FILE_PATTERN = Pattern.compile("^([^/]+)/(\\d+)_[^/]+\\.sql$");
+    private static Map<String, List<Migration>> migrationsByAppliance;
+
+    private record Migration(int version, String fileName, String path) {
+    }
+
+    /**
+     * Queues all pending migrations of the appliance on the database thread,
+     * so they run before any statement the appliance submits afterwards.
+     */
+    public static void apply(Database database, String appliance) {
+        List<Migration> migrations = findMigrations().getOrDefault(appliance, List.of());
+        if(migrations.isEmpty()) return;
+
+        if(!database.isAvailable()) {
+            Main.logger().warning(String.format("Appliance '%s' has migrations, but no database is configured", appliance));
+            return;
+        }
+
+        database.execute("migrations of " + appliance, connection -> {
+            createMigrationTable(connection);
+            Set<Integer> applied = appliedVersions(connection, appliance);
+            for(Migration migration : migrations) {
+                if(applied.contains(migration.version())) continue;
+                Main.logger().info(String.format("Applying migration %s/%s", appliance, migration.fileName()));
+                try(Statement statement = connection.createStatement()) {
+                    statement.execute(readResource(migration.path()));
+                }
+                markApplied(connection, appliance, migration);
+            }
+        });
+    }
+
+    private static synchronized Map<String, List<Migration>> findMigrations() {
+        if(migrationsByAppliance != null) return migrationsByAppliance;
+        Map<String, List<Migration>> migrations = new HashMap<>();
+        try(JarFile jar = new JarFile(pluginJar())) {
+            jar.stream()
+                .map(JarEntry::getName)
+                .filter(name -> name.startsWith(DIRECTORY))
+                .forEach(path -> {
+                    Matcher matcher = FILE_PATTERN.matcher(path.substring(DIRECTORY.length()));
+                    if(!matcher.matches()) return;
+                    String fileName = path.substring(path.lastIndexOf('/') + 1);
+                    migrations.computeIfAbsent(matcher.group(1), appliance -> new ArrayList<>())
+                        .add(new Migration(Integer.parseInt(matcher.group(2)), fileName, path));
+                });
+        } catch(IOException e) {
+            throw new IllegalStateException("Could not read migrations from plugin jar", e);
+        }
+        migrations.values().forEach(list -> list.sort(Comparator.comparingInt(Migration::version)));
+        migrationsByAppliance = migrations;
+        return migrations;
+    }
+
+    private static void createMigrationTable(Connection connection) throws SQLException {
+        try(Statement statement = connection.createStatement()) {
+            statement.execute("""
+                CREATE TABLE IF NOT EXISTS schema_migrations (
+                    appliance VARCHAR(64) NOT NULL,
+                    version INT NOT NULL,
+                    file_name VARCHAR(255) NOT NULL,
+                    applied_at DATETIME NOT NULL DEFAULT UTC_TIMESTAMP(),
+                    PRIMARY KEY (appliance, version)
+                ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
+                """);
+        }
+    }
+
+    private static Set<Integer> appliedVersions(Connection connection, String appliance) throws SQLException {
+        Set<Integer> versions = new HashSet<>();
+        try(PreparedStatement statement = connection.prepareStatement("SELECT version FROM schema_migrations WHERE appliance = ?")) {
+            statement.setString(1, appliance);
+            try(ResultSet result = statement.executeQuery()) {
+                while(result.next()) versions.add(result.getInt(1));
+            }
+        }
+        return versions;
+    }
+
+    private static void markApplied(Connection connection, String appliance, Migration migration) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement("INSERT INTO schema_migrations (appliance, version, file_name) VALUES (?, ?, ?)")) {
+            statement.setString(1, appliance);
+            statement.setInt(2, migration.version());
+            statement.setString(3, migration.fileName());
+            statement.executeUpdate();
+        }
+    }
+
+    private static String readResource(String path) throws SQLException {
+        try(InputStream stream = Main.class.getClassLoader().getResourceAsStream(path)) {
+            if(stream == null) throw new SQLException("Migration file not found: " + path);
+            return new String(stream.readAllBytes(), StandardCharsets.UTF_8);
+        } catch(IOException e) {
+            throw new SQLException("Could not read migration file " + path, e);
+        }
+    }
+
+    private static File pluginJar() {
+        try {
+            return new File(Main.class.getProtectionDomain().getCodeSource().getLocation().toURI());
+        } catch(Exception e) {
+            throw new IllegalStateException("Could not locate plugin jar", e);
+        }
+    }
+}

core/src/main/java/eu/mhsl/craftattack/spawn/core/event/LoginAttemptRecordedEvent.java

@@ -0,0 +1,48 @@
+package eu.mhsl.craftattack.spawn.core.event;
+
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.time.Instant;
+import java.util.UUID;
+
+/**
+ * Fired after a login attempt was stored in login_attempts. Called on the database thread:
+ * handlers must return quickly and must never wait for results of the shared Database.
+ */
+public class LoginAttemptRecordedEvent extends Event {
+    private static final HandlerList HANDLERS = new HandlerList();
+
+    @Override
+    public @NotNull HandlerList getHandlers() {
+        return HANDLERS;
+    }
+
+    public static HandlerList getHandlerList() {
+        return HANDLERS;
+    }
+
+    public record RecordedAttempt(
+        long id,
+        Instant at,
+        UUID uuid,
+        String name,
+        @Nullable String network,
+        String stage,
+        String result
+    ) {
+    }
+
+    private final RecordedAttempt attempt;
+
+    public LoginAttemptRecordedEvent(RecordedAttempt attempt) {
+        super(true);
+        this.attempt = attempt;
+    }
+
+    public RecordedAttempt getAttempt() {
+        return this.attempt;
+    }
+}

core/src/main/java/eu/mhsl/craftattack/spawn/core/util/network/Networks.java

@@ -0,0 +1,72 @@
+package eu.mhsl.craftattack.spawn.core.util.network;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.StringJoiner;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Groups IP addresses by internet connection: an IPv4 address stands for itself,
+ * an IPv6 address for its /64 prefix (one prefix per household line).
+ */
+public final class Networks {
+    private static final Pattern IPV4 = Pattern.compile("^(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})$");
+    private static final Pattern IPV6 = Pattern.compile("^[0-9a-fA-F:.]*:[0-9a-fA-F:.]*$");
+    private static final String IPV6_SUFFIX = "::/64";
+
+    private Networks() {
+    }
+
+    /**
+     * @return the connection key ("93.204.10.20" or "2003:e1:1f00:ab00::/64"), or null if the text is no IP address
+     */
+    public static @Nullable String networkOf(@Nullable String ip) {
+        if(ip == null) return null;
+        String text = ip.trim();
+
+        Matcher ipv4 = IPV4.matcher(text);
+        if(ipv4.matches()) return ipv4Of(ipv4);
+        if(!IPV6.matcher(text).matches()) return null;
+
+        InetAddress address;
+        try {
+            // the text contains a colon, so it is parsed as IPv6 literal and never resolved via DNS
+            address = InetAddress.getByName(text);
+        } catch(UnknownHostException e) {
+            return null;
+        }
+        if(address instanceof Inet4Address) return address.getHostAddress();
+        byte[] bytes = address.getAddress();
+        return String.format("%x:%x:%x:%x%s", group(bytes, 0), group(bytes, 2), group(bytes, 4), group(bytes, 6), IPV6_SUFFIX);
+    }
+
+    /**
+     * Shortened form for display: "93.204.x.x" or "2003:e1:x:x::/64".
+     */
+    public static String mask(String network) {
+        if(network.endsWith(IPV6_SUFFIX)) {
+            String[] groups = network.substring(0, network.length() - IPV6_SUFFIX.length()).split(":");
+            return groups[0] + ":" + groups[1] + ":x:x" + IPV6_SUFFIX;
+        }
+        String[] octets = network.split("\\.");
+        return octets.length == 4 ? octets[0] + "." + octets[1] + ".x.x" : network;
+    }
+
+    private static @Nullable String ipv4Of(Matcher matcher) {
+        StringJoiner joiner = new StringJoiner(".");
+        for(int i = 1; i <= 4; i++) {
+            int octet = Integer.parseInt(matcher.group(i));
+            if(octet > 255) return null;
+            joiner.add(Integer.toString(octet));
+        }
+        return joiner.toString();
+    }
+
+    private static int group(byte[] bytes, int offset) {
+        return ((bytes[offset] & 0xff) << 8) | (bytes[offset + 1] & 0xff);
+    }
+}

core/src/main/java/eu/mhsl/craftattack/spawn/core/util/server/Floodgate.java

@@ -5,21 +5,32 @@ import org.geysermc.cumulus.form.SimpleForm;
 import org.geysermc.floodgate.api.FloodgateApi;
 import org.geysermc.floodgate.api.player.FloodgatePlayer;
 
+import java.util.UUID;
 import java.util.function.Consumer;
 
 public class Floodgate {
-    private static final FloodgateApi instance = FloodgateApi.getInstance();
+    private static FloodgateApi api() {
+        return FloodgateApi.getInstance();
+    }
 
     public static boolean isBedrock(Player p) {
-        return instance.isFloodgatePlayer(p.getUniqueId());
+        return api().isFloodgatePlayer(p.getUniqueId());
+    }
+
+    /**
+     * Whether the UUID has the format Floodgate uses for Bedrock players (most significant bits zero).
+     * Works without the player being online and without the Floodgate API.
+     */
+    public static boolean isFloodgateUuid(UUID uuid) {
+        return uuid.getMostSignificantBits() == 0;
     }
 
     public static FloodgatePlayer getBedrockPlayer(Player p) {
-        return instance.getPlayer(p.getUniqueId());
+        return api().getPlayer(p.getUniqueId());
     }
 
     public static void runBedrockOnly(Player p, Consumer<FloodgatePlayer> callback) {
-        if(isBedrock(p)) callback.accept(instance.getPlayer(p.getUniqueId()));
+        if(isBedrock(p)) callback.accept(api().getPlayer(p.getUniqueId()));
     }
 
     public static void runJavaOnly(Player p, Consumer<Player> callback) {

core/src/main/resources/config.yml

@@ -7,6 +7,22 @@ api:
   secret: secret
   baseurl: https://mhsl.eu/craftattack/api/
 
+database:
+  host:
+  port: 3306
+  name: craftattack
+  user:
+  password:
+
+loginLog:
+  retentionMonths: 16
+
+banEvasion:
+  windowDays: 14
+  rejectionWindowHours: 24
+  banCacheMinutes: 5
+  retentionMonths: 16
+
 worldMuseum:
   uuid:
   connect-server-name: worldmuseum

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/api/repositories/WhitelistRepository.java

@@ -4,6 +4,7 @@ import eu.mhsl.craftattack.spawn.core.api.client.HttpRepository;
 import eu.mhsl.craftattack.spawn.core.api.client.ReqResp;
 import eu.mhsl.craftattack.spawn.common.api.CraftAttackApi;
 
+import java.time.Duration;
 import java.util.List;
 import java.util.UUID;
 
@@ -29,4 +30,12 @@ public class WhitelistRepository extends HttpRepository {
             UserData.class
         );
     }
+
+    public ReqResp<UserData> getUserData(UUID userId, Duration timeout) {
+        return this.get(
+            "users/%s".formatted(userId.toString()),
+            timeout,
+            UserData.class
+        );
+    }
 }

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/AccountLinksCommand.java

@@ -0,0 +1,34 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import eu.mhsl.craftattack.spawn.core.appliance.ApplianceCommand;
+import eu.mhsl.craftattack.spawn.core.util.server.Floodgate;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * /accountLinks – list of suspected cases; /accountLinks <player> – accounts sharing a connection with the player.
+ * Only visible to admins.
+ */
+class AccountLinksCommand extends ApplianceCommand.PlayerChecked<BanEvasion> {
+    AccountLinksCommand() {
+        super("accountLinks");
+    }
+
+    @Override
+    public @Nullable String permission() {
+        return BanEvasion.ADMIN_PERMISSION;
+    }
+
+    @Override
+    protected void execute(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        Player player = this.getPlayer();
+        if(Floodgate.isBedrock(player)) throw new Error("Nur für Java-Clients");
+        if(!this.getAppliance().isActive()) throw new Error("Keine Datenbank konfiguriert");
+
+        if(args.length == 0) this.getAppliance().dialogs().openList(player, CaseStatus.OPEN);
+        else this.getAppliance().dialogs().openLinks(player, args[0]);
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/AdminNotifier.java

@@ -0,0 +1,78 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.format.NamedTextColor;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Player;
+
+import java.util.Comparator;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * Chat messages to online admins. Never contains IP addresses.
+ */
+final class AdminNotifier {
+    record Notice(
+        long caseId,
+        String firstName,
+        boolean firstBanned,
+        String secondName,
+        boolean secondBanned,
+        Severity severity,
+        Set<Reason> reasons,
+        boolean reopened
+    ) {
+    }
+
+    private final BanEvasion appliance;
+
+    AdminNotifier(BanEvasion appliance) {
+        this.appliance = appliance;
+    }
+
+    void announce(Notice notice) {
+        Bukkit.getScheduler().runTask(Main.instance(), () -> {
+            Component message = this.format(notice);
+            Bukkit.getOnlinePlayers().stream()
+                .filter(player -> player.hasPermission(BanEvasion.ADMIN_PERMISSION))
+                .forEach(player -> player.sendMessage(message));
+        });
+    }
+
+    void announceOpenCases(Player admin, BanEvasionRepository.OpenCount count) {
+        if(count.total() == 0) return;
+        String text = count.total() == 1 ? "1 offener Verdachtsfall" : count.total() + " offene Verdachtsfälle";
+        admin.sendMessage(Component.text()
+            .append(Component.text("⚑ " + text, count.high() > 0 ? NamedTextColor.RED : NamedTextColor.GRAY))
+            .append(Component.text(count.high() > 0 ? " (" + count.high() + " hoch)" : "", NamedTextColor.RED))
+            .append(Component.text(" [Liste]", NamedTextColor.GOLD)
+                .clickEvent(BanEvasionDialogs.adminClick(player -> this.appliance.dialogs().openList(player, CaseStatus.OPEN))))
+            .build());
+    }
+
+    private Component format(Notice notice) {
+        long caseId = notice.caseId();
+        NamedTextColor color = notice.severity() == Severity.HIGH ? NamedTextColor.RED : NamedTextColor.GRAY;
+        String reasons = notice.reasons().stream()
+            .filter(reason -> !reason.informational)
+            .sorted(Comparator.reverseOrder())
+            .map(reason -> reason.label)
+            .collect(Collectors.joining(", "));
+        return Component.text()
+            .append(Component.text(String.format("⚑ %s [%s]: ", notice.reopened() ? "Wieder offen" : "Verdacht", notice.severity().label), color))
+            .append(account(notice.firstName(), notice.firstBanned()))
+            .append(Component.text(" ↔ ", color))
+            .append(account(notice.secondName(), notice.secondBanned()))
+            .append(Component.text(" – " + reasons + " ", color))
+            .append(Component.text("[Öffnen]", NamedTextColor.GOLD)
+                .clickEvent(BanEvasionDialogs.adminClick(player -> this.appliance.dialogs().openCase(player, caseId, false))))
+            .build();
+    }
+
+    private static Component account(String name, boolean banned) {
+        Component component = Component.text(name, NamedTextColor.WHITE);
+        return banned ? component.append(Component.text(" (gebannt)", NamedTextColor.RED)) : component;
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/Attempt.java

@@ -0,0 +1,31 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import eu.mhsl.craftattack.spawn.core.event.LoginAttemptRecordedEvent;
+
+import java.time.Instant;
+import java.util.UUID;
+
+/**
+ * One row of login_attempts with a known connection key.
+ */
+record Attempt(long id, Instant at, UUID uuid, String name, String network, String stage, String result) {
+    private static final String STAGE_WEBSITE = "WEBSITE";
+
+    /**
+     * Only for attempts with a known connection key.
+     */
+    static Attempt of(LoginAttemptRecordedEvent.RecordedAttempt recorded) {
+        return new Attempt(recorded.id(), recorded.at(), recorded.uuid(), recorded.name(), recorded.network(), recorded.stage(), recorded.result());
+    }
+
+    boolean isWebsiteSignup() {
+        return STAGE_WEBSITE.equals(this.stage) && "SIGNUP".equals(this.result);
+    }
+
+    /**
+     * Rejected by the server (whitelist, ban, maintenance, ...), not merely aborted by the client.
+     */
+    boolean isRejection() {
+        return !STAGE_WEBSITE.equals(this.stage) && this.result.startsWith("KICK_");
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/BanEvasion.java

@@ -0,0 +1,322 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+import eu.mhsl.craftattack.spawn.core.api.HttpStatus;
+import eu.mhsl.craftattack.spawn.core.api.client.ReqResp;
+import eu.mhsl.craftattack.spawn.core.appliance.Appliance;
+import eu.mhsl.craftattack.spawn.core.appliance.ApplianceCommand;
+import eu.mhsl.craftattack.spawn.core.database.Database;
+import eu.mhsl.craftattack.spawn.core.event.LoginAttemptRecordedEvent;
+import eu.mhsl.craftattack.spawn.core.util.network.Networks;
+import eu.mhsl.craftattack.spawn.craftattack.api.repositories.WhitelistRepository;
+import eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.strikes.Strikes;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.format.NamedTextColor;
+import org.bukkit.Bukkit;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Listener;
+import org.bukkit.scheduler.BukkitTask;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.net.InetSocketAddress;
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.function.Consumer;
+import java.util.logging.Level;
+
+/**
+ * Detects possible ban evasion: accounts that shared an internet connection (IPv4 address or IPv6 /64)
+ * within a time window, judged together with bans from the website. Only reports to admins
+ * (chat and dialogs via /accountLinks), never punishes and never changes the login of players.
+ * Rules: CaseEvaluator, deduplication: CaseDecision, storage: BanEvasionRepository.
+ * Evaluations and dialog queries run on an own worker thread, never on the main or database thread.
+ */
+public class BanEvasion extends Appliance {
+    static final String ADMIN_PERMISSION = "admin";
+    private static final long TICKS_PER_MINUTE = 20L * 60;
+    private static final long TICKS_PER_DAY = TICKS_PER_MINUTE * 60 * 24;
+    private static final Duration BAN_LOOKUP_TIMEOUT = Duration.ofSeconds(5);
+    private static final Duration BAN_LOOKUP_BACKOFF = Duration.ofSeconds(30);
+
+    @FunctionalInterface
+    interface Loader<T> {
+        T load() throws Exception;
+    }
+
+    /**
+     * Everything an evaluation needs from the database, loaded in one go.
+     */
+    private record Context(List<Attempt> partners, Map<UUID, Long> households, Map<Long, Set<UUID>> householdMembers) {
+    }
+
+    private final BanEvasionRepository repository = new BanEvasionRepository();
+    private final OnlineNetworks onlineNetworks = new OnlineNetworks();
+    private Database database;
+    private ExecutorService worker;
+    private BukkitTask retentionTask;
+    private BanStatusCache banStatus;
+    private AdminNotifier notifier;
+    private BanEvasionDialogs dialogs;
+    private Duration window;
+    private Duration rejectionWindow;
+    private int retentionMonths;
+    private volatile boolean active;
+
+    public BanEvasion() {
+        super("banEvasion");
+    }
+
+    @Override
+    public void onEnable() {
+        this.database = Main.instance().getDatabase();
+        if(!this.database.isAvailable()) {
+            Main.logger().warning("BanEvasion: no database configured, ban evasion detection is disabled");
+            return;
+        }
+        ConfigurationSection config = this.localConfig();
+        this.window = Duration.ofDays(config.getInt("windowDays", 14));
+        this.rejectionWindow = Duration.ofHours(config.getInt("rejectionWindowHours", 24));
+        this.retentionMonths = config.getInt("retentionMonths", 16);
+        this.banStatus = new BanStatusCache(this::lookupBanState, Duration.ofMinutes(config.getInt("banCacheMinutes", 5)), BAN_LOOKUP_BACKOFF, Clock.systemUTC());
+        this.worker = Executors.newSingleThreadExecutor(runnable -> {
+            Thread thread = new Thread(runnable, "Spawn-BanEvasion");
+            thread.setDaemon(true);
+            return thread;
+        });
+        this.notifier = new AdminNotifier(this);
+        this.dialogs = new BanEvasionDialogs(this);
+        this.retentionTask = Bukkit.getScheduler().runTaskTimerAsynchronously(Main.instance(), this::deleteExpired, TICKS_PER_MINUTE, TICKS_PER_DAY);
+        this.active = true;
+    }
+
+    @Override
+    public void onDisable() {
+        this.active = false;
+        if(this.retentionTask != null) this.retentionTask.cancel();
+        if(this.worker != null) this.worker.shutdownNow();
+    }
+
+    boolean isActive() {
+        return this.active;
+    }
+
+    BanEvasionRepository repository() {
+        return this.repository;
+    }
+
+    BanEvasionDialogs dialogs() {
+        return this.dialogs;
+    }
+
+    /**
+     * Runs the query on the database thread and waits for it. Only for the worker thread.
+     */
+    <T> T query(Database.SqlQuery<T> query) {
+        return this.database.query(query).join();
+    }
+
+    /**
+     * Blocks for HTTP requests. Only for the worker thread.
+     */
+    Map<UUID, BanState> banStates(Collection<UUID> uuids) {
+        return this.banStatus.getAll(uuids);
+    }
+
+    /**
+     * Loads data on the worker thread and hands it to the main thread, if the admin is still online.
+     */
+    <T> void loadFor(Player admin, Loader<T> loader, Consumer<T> onMainThread) {
+        if(!this.active) return;
+        this.submit(() -> {
+            T result;
+            try {
+                result = loader.load();
+            } catch(Exception e) {
+                Main.logger().log(Level.WARNING, "BanEvasion: loading data for " + admin.getName() + " failed", e);
+                Bukkit.getScheduler().runTask(Main.instance(), () -> admin.sendMessage(Component.text("Fehler beim Laden der Daten.", NamedTextColor.RED)));
+                return;
+            }
+            Bukkit.getScheduler().runTask(Main.instance(), () -> {
+                if(admin.isOnline()) onMainThread.accept(result);
+            });
+        });
+    }
+
+    /**
+     * Shortcut of {@link #loadFor} for a single database query.
+     */
+    <T> void queryFor(Player admin, Database.SqlQuery<T> query, Consumer<T> onMainThread) {
+        this.loadFor(admin, () -> this.query(query), onMainThread);
+    }
+
+    /**
+     * Runs a database change for the admin, then continues on the main thread.
+     */
+    void runFor(Player admin, Database.SqlAction action, Runnable onMainThread) {
+        this.queryFor(admin, connection -> {
+            action.run(connection);
+            return true;
+        }, done -> onMainThread.run());
+    }
+
+    /**
+     * Called on the database thread: hands the attempt to the worker without waiting.
+     */
+    void onAttemptRecorded(LoginAttemptRecordedEvent.RecordedAttempt recorded) {
+        if(!this.active || recorded.network() == null) return;
+        Attempt attempt = Attempt.of(recorded);
+        Set<UUID> online = this.onlineNetworks.onlineOn(attempt.network());
+        this.submit(() -> this.evaluate(attempt, online));
+    }
+
+    void playerJoined(Player player) {
+        InetSocketAddress address = player.getAddress();
+        String network = address == null || address.getAddress() == null ? null : Networks.networkOf(address.getAddress().getHostAddress());
+        this.onlineNetworks.joined(player.getUniqueId(), network);
+        if(!this.active || !player.hasPermission(ADMIN_PERMISSION)) return;
+        this.queryFor(player, this.repository::countOpen, count -> this.notifier.announceOpenCases(player, count));
+    }
+
+    void playerLeft(Player player) {
+        this.onlineNetworks.left(player.getUniqueId());
+    }
+
+    private void submit(Runnable task) {
+        try {
+            this.worker.execute(task);
+        } catch(RejectedExecutionException e) {
+            Main.logger().warning("BanEvasion: worker stopped, task dropped");
+        }
+    }
+
+    private void evaluate(Attempt attempt, Set<UUID> online) {
+        try {
+            Context context = this.query(connection -> this.loadContext(connection, attempt));
+            if(context == null) return;
+
+            Set<UUID> banStateNeeded = new HashSet<>();
+            banStateNeeded.add(attempt.uuid());
+            context.partners().forEach(partner -> banStateNeeded.add(partner.uuid()));
+            context.householdMembers().values().forEach(banStateNeeded::addAll);
+            Map<UUID, BanState> banStates = this.banStatus.getAll(banStateNeeded);
+
+            List<PairFinding> findings = CaseEvaluator.evaluate(new CaseEvaluator.Input(
+                attempt, context.partners(), banStates, context.households(), context.householdMembers(), online, this.rejectionWindow
+            ));
+            if(findings.isEmpty()) return;
+
+            // partner attempts are ordered by time, so the last one carries the latest name
+            Map<UUID, String> names = new HashMap<>();
+            context.partners().forEach(partner -> names.put(partner.uuid(), partner.name()));
+            names.put(attempt.uuid(), attempt.name());
+
+            List<AdminNotifier.Notice> notices = this.query(connection -> {
+                List<AdminNotifier.Notice> announced = new ArrayList<>();
+                for(PairFinding finding : findings) {
+                    AdminNotifier.Notice notice = this.applyFinding(connection, finding, attempt, banStates, names);
+                    if(notice != null) announced.add(notice);
+                }
+                return announced;
+            });
+            notices.forEach(this.notifier::announce);
+        } catch(Exception e) {
+            Main.logger().log(Level.WARNING, String.format("BanEvasion: evaluating login attempt #%d failed", attempt.id()), e);
+        }
+    }
+
+    /**
+     * @return null if the attempt is exempted or nobody else used the connection within the window
+     */
+    private @Nullable Context loadContext(Connection connection, Attempt attempt) throws SQLException {
+        if(this.repository.isExempt(connection, attempt.network(), attempt.at())) return null;
+        List<Attempt> partners = this.repository.partnerAttempts(connection, attempt, this.window);
+        if(partners.isEmpty()) return null;
+
+        Set<UUID> involved = new HashSet<>();
+        involved.add(attempt.uuid());
+        partners.forEach(partner -> involved.add(partner.uuid()));
+        Map<UUID, Long> households = this.repository.householdsOf(connection, involved);
+        return new Context(partners, households, this.repository.householdMembers(connection, new HashSet<>(households.values())));
+    }
+
+    private @Nullable AdminNotifier.Notice applyFinding(
+        Connection connection,
+        PairFinding finding,
+        Attempt attempt,
+        Map<UUID, BanState> banStates,
+        Map<UUID, String> names
+    ) throws SQLException {
+        CaseDecision.ExistingCase existing = this.repository.findCase(connection, finding.first(), finding.second());
+        CaseDecision.Result decision = CaseDecision.decide(existing, finding);
+        long caseId;
+        if(existing == null) {
+            caseId = this.repository.createCase(connection, finding, attempt.at());
+        } else {
+            caseId = existing.id();
+            this.repository.updateCase(connection, caseId, finding, attempt.at(), decision.reopen());
+        }
+        this.repository.addReasons(connection, caseId, finding.reasons(), decision.newReasons(), attempt.id(), attempt.at());
+
+        if(existing == null || !decision.newReasons().isEmpty()) {
+            String change = existing == null ? "created" : decision.reopen() ? "reopened" : "updated";
+            Main.logger().info(String.format("BanEvasion: case #%d %s %s", caseId, change, decision.newReasons()));
+        }
+        if(!decision.announce()) return null;
+        return new AdminNotifier.Notice(
+            caseId,
+            names.get(finding.first()),
+            banStates.get(finding.first()) == BanState.BANNED,
+            names.get(finding.second()),
+            banStates.get(finding.second()) == BanState.BANNED,
+            finding.severity(),
+            finding.reasons().keySet(),
+            decision.reopen()
+        );
+    }
+
+    private BanState lookupBanState(UUID uuid) {
+        try {
+            ReqResp<WhitelistRepository.UserData> response = this.queryRepository(WhitelistRepository.class).getUserData(uuid, BAN_LOOKUP_TIMEOUT);
+            if(response.status() == HttpStatus.NOT_FOUND) return BanState.NOT_BANNED;
+            if(response.status() != HttpStatus.OK || response.data() == null) return BanState.UNKNOWN;
+            List<WhitelistRepository.UserData.Strike> strikes = Objects.requireNonNullElse(response.data().strikes(), List.of());
+            return this.queryAppliance(Strikes.class).isBanned(strikes).isBanned() ? BanState.BANNED : BanState.NOT_BANNED;
+        } catch(RuntimeException e) {
+            Main.logger().warning("BanEvasion: ban state of " + uuid + " unavailable: " + e.getMessage());
+            return BanState.UNKNOWN;
+        }
+    }
+
+    private void deleteExpired() {
+        this.database.execute("deleting expired ban evasion data", connection -> {
+            int deleted = this.repository.deleteExpired(connection, this.retentionMonths);
+            if(deleted > 0) Main.logger().info(String.format("BanEvasion: deleted %d expired cases and exemptions", deleted));
+        });
+    }
+
+    @Override
+    protected @NotNull List<Listener> listeners() {
+        return List.of(new BanEvasionListener());
+    }
+
+    @Override
+    protected @NotNull List<ApplianceCommand<?>> commands() {
+        return List.of(new AccountLinksCommand());
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/BanEvasionDialogs.java

@@ -0,0 +1,443 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import eu.mhsl.craftattack.spawn.core.Main;
+import eu.mhsl.craftattack.spawn.core.util.network.Networks;
+import io.papermc.paper.dialog.Dialog;
+import io.papermc.paper.dialog.DialogResponseView;
+import io.papermc.paper.registry.data.dialog.ActionButton;
+import io.papermc.paper.registry.data.dialog.DialogBase;
+import io.papermc.paper.registry.data.dialog.action.DialogAction;
+import io.papermc.paper.registry.data.dialog.body.DialogBody;
+import io.papermc.paper.registry.data.dialog.input.DialogInput;
+import io.papermc.paper.registry.data.dialog.input.SingleOptionDialogInput;
+import io.papermc.paper.registry.data.dialog.type.DialogType;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.JoinConfiguration;
+import net.kyori.adventure.text.event.ClickCallback;
+import net.kyori.adventure.text.event.ClickEvent;
+import net.kyori.adventure.text.format.NamedTextColor;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.Nullable;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+
+/**
+ * Admin dialogs of the ban evasion detection. Every button checks the admin permission again on the server
+ * and captures only the ids it needs, so the registered callbacks stay small.
+ */
+final class BanEvasionDialogs {
+    private static final int LIST_LIMIT = 30;
+    private static final int LINK_LIMIT = 30;
+    private static final int TIMELINE_LIMIT = 20;
+    private static final int RECENT_NETWORKS = 5;
+    private static final int BUTTON_WIDTH = 310;
+    private static final int BODY_WIDTH = 400;
+    private static final ClickCallback.Options CHAT_CALLBACK = ClickCallback.Options.builder()
+        .uses(ClickCallback.UNLIMITED_USES).lifetime(Duration.ofHours(12)).build();
+    private static final ClickCallback.Options DIALOG_CALLBACK = ClickCallback.Options.builder()
+        .uses(ClickCallback.UNLIMITED_USES).lifetime(Duration.ofMinutes(30)).build();
+    private static final DateTimeFormatter TIME = DateTimeFormatter.ofPattern("dd.MM.yy HH:mm").withZone(ZoneId.of("Europe/Berlin"));
+    private static final String NOTE_KEY = "note";
+    private static final String NETWORK_KEY = "network";
+    private static final String HOURS_KEY = "hours";
+
+    private record CaseView(BanEvasionRepository.CaseDetails details, Map<UUID, BanState> banStates, Map<UUID, Long> households) {
+    }
+
+    private record LinksView(String name, List<BanEvasionRepository.Link> links, List<String> networks, @Nullable Long household) {
+    }
+
+    private record HouseholdView(BanEvasionRepository.Household household, Map<UUID, BanState> banStates) {
+    }
+
+    private final BanEvasion appliance;
+    private final BanEvasionRepository repository;
+
+    BanEvasionDialogs(BanEvasion appliance) {
+        this.appliance = appliance;
+        this.repository = appliance.repository();
+    }
+
+    /**
+     * Click event for chat messages that only works for admins.
+     */
+    static ClickEvent<?> adminClick(Consumer<Player> action) {
+        return ClickEvent.callback(audience -> {
+            if(audience instanceof Player player && player.hasPermission(BanEvasion.ADMIN_PERMISSION)) action.accept(player);
+        }, CHAT_CALLBACK);
+    }
+
+    void openList(Player admin, CaseStatus status) {
+        this.appliance.queryFor(admin, connection -> this.repository.listCases(connection, status, LIST_LIMIT), cases -> {
+            List<ActionButton> buttons = new ArrayList<>();
+            cases.forEach(summary -> {
+                long caseId = summary.id();
+                buttons.add(button(caseLabel(summary), player -> this.openCase(player, caseId, false)));
+            });
+            CaseStatus other = status == CaseStatus.OPEN ? CaseStatus.CLOSED : CaseStatus.OPEN;
+            buttons.add(button(other == CaseStatus.OPEN ? "Offene Fälle" : "Geschlossene Fälle", player -> this.openList(player, other)));
+            buttons.add(button("Haushalte", this::openHouseholds));
+            buttons.add(button("IP-Ausnahmen", this::openExemptions));
+
+            Component body = cases.isEmpty()
+                ? Component.text("Keine Fälle.")
+                : Component.text(String.format("%d Fälle (höchstens %d), hohe zuerst, dann neueste.", cases.size(), LIST_LIMIT));
+            show(admin, status == CaseStatus.OPEN ? "Verdachtsfälle – offen" : "Verdachtsfälle – geschlossen", body, List.of(), buttons);
+        });
+    }
+
+    void openCase(Player admin, long caseId, boolean fullNetworks) {
+        this.appliance.loadFor(admin, () -> {
+            record Loaded(BanEvasionRepository.CaseDetails details, Map<UUID, Long> households) {
+            }
+            Loaded loaded = this.appliance.query(connection -> {
+                BanEvasionRepository.CaseDetails details = this.repository.loadCase(connection, caseId, TIMELINE_LIMIT);
+                if(details == null) return null;
+                return new Loaded(details, this.repository.householdsOf(connection, List.of(details.summary().first(), details.summary().second())));
+            });
+            if(loaded == null) return null;
+            List<UUID> accounts = List.of(loaded.details().summary().first(), loaded.details().summary().second());
+            return new CaseView(loaded.details(), this.appliance.banStates(accounts), loaded.households());
+        }, view -> {
+            if(view == null) {
+                admin.sendMessage(Component.text("Fall #" + caseId + " gibt es nicht (mehr).", NamedTextColor.RED));
+                return;
+            }
+            this.showCase(admin, view, fullNetworks);
+        });
+    }
+
+    void openLinks(Player admin, String name) {
+        this.appliance.queryFor(admin, connection -> {
+            BanEvasionRepository.Member account = this.repository.accountByName(connection, name);
+            return account == null ? null : this.loadLinks(connection, account.uuid(), account.name());
+        }, view -> {
+            if(view == null) admin.sendMessage(Component.text("Keine Einträge zu " + name + ".", NamedTextColor.RED));
+            else this.showLinks(admin, view);
+        });
+    }
+
+    void openLinks(Player admin, UUID uuid) {
+        this.appliance.queryFor(admin, connection -> this.loadLinks(connection, uuid, this.repository.nameOf(connection, uuid)),
+            view -> this.showLinks(admin, view));
+    }
+
+    void openNewExemption(Player admin, List<String> networks) {
+        List<SingleOptionDialogInput.OptionEntry> options = new ArrayList<>();
+        for(int i = 0; i < networks.size(); i++)
+            options.add(SingleOptionDialogInput.OptionEntry.create(networks.get(i), Component.text(networks.get(i)), i == 0));
+        List<DialogInput> inputs = List.of(
+            DialogInput.singleOption(NETWORK_KEY, Component.text("Anschluss"), options).width(BODY_WIDTH).build(),
+            DialogInput.numberRange(HOURS_KEY, Component.text("Dauer in Stunden"), 1, 168).step(1f).initial(12f).width(BODY_WIDTH).build(),
+            noteInput("Notiz, z. B. LAN-Party bei …")
+        );
+        List<ActionButton> buttons = List.of(
+            inputButton("Ausnahme anlegen", (player, response) -> this.createExemption(player, networks, response)),
+            this.backToList("Abbrechen")
+        );
+        show(admin, "IP-Ausnahme anlegen",
+            Component.text("Einträge von diesem Anschluss lösen in der gewählten Zeit keine Meldung aus. Sie werden weiter protokolliert."),
+            inputs, buttons);
+    }
+
+    void openExemptions(Player admin) {
+        Instant now = Instant.now();
+        this.appliance.queryFor(admin, connection -> this.repository.activeExemptions(connection, now), exemptions -> {
+            Component body = Component.text(exemptions.isEmpty()
+                ? "Keine aktiven IP-Ausnahmen."
+                : exemptions.size() + " aktive IP-Ausnahmen, zuerst endende oben.");
+            List<ActionButton> buttons = new ArrayList<>();
+            exemptions.forEach(exemption -> buttons.add(button(
+                String.format("%s bis %s%s", Networks.mask(exemption.network()), TIME.format(exemption.validUntil()),
+                    exemption.note() == null ? "" : " · " + exemption.note()),
+                player -> this.showExemption(player, exemption))));
+            buttons.add(this.backToList("Zur Fallliste"));
+            show(admin, "IP-Ausnahmen", body, List.of(), buttons);
+        });
+    }
+
+    void openHouseholds(Player admin) {
+        this.appliance.queryFor(admin, this.repository::listHouseholds, households -> {
+            String text = households.isEmpty() ? "Keine Haushalte." : households.size() + " Haushalte, neueste zuerst.";
+            if(households.size() > LIST_LIMIT)
+                text += " Gezeigt werden die neuesten " + LIST_LIMIT + " – ältere über /accountLinks <spieler> finden.";
+            List<ActionButton> buttons = new ArrayList<>();
+            households.stream().limit(LIST_LIMIT).forEach(household -> {
+                long householdId = household.id();
+                buttons.add(button(
+                    "#" + householdId + ": " + household.members().stream().map(BanEvasionRepository.Member::name).collect(Collectors.joining(", ")),
+                    player -> this.openHousehold(player, householdId)));
+            });
+            buttons.add(this.backToList("Zur Fallliste"));
+            show(admin, "Haushalte", Component.text(text), List.of(), buttons);
+        });
+    }
+
+    void openHousehold(Player admin, long householdId) {
+        this.appliance.loadFor(admin, () -> {
+            BanEvasionRepository.Household household = this.appliance.query(connection -> this.repository.household(connection, householdId));
+            if(household == null) return null;
+            return new HouseholdView(household, this.appliance.banStates(household.members().stream().map(BanEvasionRepository.Member::uuid).toList()));
+        }, view -> {
+            if(view == null) {
+                admin.sendMessage(Component.text("Haushalt #" + householdId + " gibt es nicht (mehr).", NamedTextColor.GRAY));
+                this.openHouseholds(admin);
+                return;
+            }
+            BanEvasionRepository.Household household = view.household();
+            List<Component> lines = new ArrayList<>();
+            lines.add(Component.text("Angelegt " + TIME.format(household.createdAt()) + " von " + orUnknown(household.createdByName())));
+            lines.add(Component.text("Notiz: " + (household.note() == null ? "–" : household.note())));
+            lines.add(Component.empty());
+            household.members().forEach(member -> lines.add(accountLine(member.name(), view.banStates().get(member.uuid()), null)));
+
+            List<ActionButton> buttons = new ArrayList<>();
+            household.members().forEach(member -> buttons.add(button("Entfernen: " + member.name(), player -> this.removeMember(player, householdId, member))));
+            buttons.add(button("Zurück", this::openHouseholds));
+            show(admin, "Haushalt #" + householdId, lines(lines), List.of(), buttons);
+        });
+    }
+
+    private LinksView loadLinks(Connection connection, UUID uuid, String name) throws SQLException {
+        return new LinksView(
+            name,
+            this.repository.linksOf(connection, uuid, LINK_LIMIT),
+            this.repository.recentNetworks(connection, uuid, RECENT_NETWORKS),
+            this.repository.householdsOf(connection, List.of(uuid)).get(uuid)
+        );
+    }
+
+    private void showLinks(Player admin, LinksView view) {
+        String name = view.name();
+        Long household = view.household();
+        List<String> networks = view.networks();
+        List<Component> lines = new ArrayList<>();
+        if(household != null) lines.add(Component.text(name + " gehört zu Haushalt #" + household + "."));
+        if(view.links().isEmpty()) lines.add(Component.text("Kein anderer Account hat je einen Anschluss mit " + name + " geteilt."));
+        view.links().forEach(link -> lines.add(Component.text(String.format("%s – %d Einträge an gemeinsamen Anschlüssen, %s bis %s%s",
+            link.name(), link.sharedAttempts(), TIME.format(link.firstAt()), TIME.format(link.lastAt()),
+            link.caseId() == null ? "" : " · Fall #" + link.caseId()))));
+
+        List<ActionButton> buttons = new ArrayList<>();
+        if(household != null) buttons.add(button("Haushalt #" + household, player -> this.openHousehold(player, household)));
+        view.links().forEach(link -> {
+            Long caseId = link.caseId();
+            if(caseId != null) buttons.add(button("Fall #" + caseId + ": " + link.name(), player -> this.openCase(player, caseId, false)));
+        });
+        if(!networks.isEmpty()) buttons.add(button("IP-Ausnahme für Anschluss von " + name, player -> this.openNewExemption(player, networks)));
+        buttons.add(this.backToList("Zur Fallliste"));
+        show(admin, "Accounts zu " + name, lines(lines), List.of(), buttons);
+    }
+
+    private void showExemption(Player admin, BanEvasionRepository.Exemption exemption) {
+        long exemptionId = exemption.id();
+        Component body = lines(List.of(
+            Component.text("Anschluss: " + exemption.network()),
+            Component.text("Gültig: " + TIME.format(exemption.validFrom()) + " bis " + TIME.format(exemption.validUntil())),
+            Component.text("Angelegt von: " + orUnknown(exemption.createdByName())),
+            Component.text("Notiz: " + (exemption.note() == null ? "–" : exemption.note()))
+        ));
+        show(admin, "IP-Ausnahme", body, List.of(), List.of(
+            button("Jetzt beenden", player -> this.endExemption(player, exemptionId)),
+            button("Zurück", this::openExemptions)
+        ));
+    }
+
+    private void showCase(Player admin, CaseView view, boolean fullNetworks) {
+        BanEvasionRepository.CaseDetails details = view.details();
+        BanEvasionRepository.CaseSummary summary = details.summary();
+        List<Component> lines = new ArrayList<>();
+        lines.add(Component.text(String.format("Status: %s%s · Stärke: %s · %d Treffer",
+            summary.status() == CaseStatus.OPEN ? "offen" : "geschlossen",
+            summary.outcome() == null ? "" : " (" + summary.outcome().label + ")",
+            summary.severity().label, summary.hits())));
+        lines.add(Component.text("Erstellt " + TIME.format(details.createdAt()) + " · zuletzt " + TIME.format(summary.lastSeenAt())));
+        if(details.banStatusUnknown())
+            lines.add(Component.text("Bann-Status war bei der letzten Prüfung nicht abrufbar.", NamedTextColor.GOLD));
+        lines.add(Component.empty());
+        lines.add(accountLine(summary.firstName(), view.banStates().get(summary.first()), view.households().get(summary.first())));
+        lines.add(accountLine(summary.secondName(), view.banStates().get(summary.second()), view.households().get(summary.second())));
+        lines.add(Component.empty());
+        lines.add(Component.text("Gründe:"));
+        details.reasons().forEach(reason -> lines.add(Component.text(
+            String.format("• %s (%s) seit %s", reason.reason().label, reason.severity().label, TIME.format(reason.firstSeenAt())),
+            reason.severity() == Severity.HIGH && !reason.reason().informational ? NamedTextColor.RED : NamedTextColor.GRAY)));
+        lines.add(Component.empty());
+        lines.add(Component.text("Gemeinsame Anschlüsse: " + networks(details.sharedNetworks(), fullNetworks)));
+        lines.add(Component.empty());
+        lines.add(Component.text("Letzte Einträge:"));
+        details.timeline().forEach(entry -> lines.add(Component.text(String.format("%s  %s  %s %s  %s",
+            TIME.format(entry.at()), entry.name(), entry.stage(), entry.result(),
+            entry.network() == null ? "?" : network(entry.network(), fullNetworks)), NamedTextColor.GRAY)));
+        if(details.closedAt() != null) {
+            lines.add(Component.empty());
+            lines.add(Component.text(String.format("Zuletzt geschlossen %s von %s%s",
+                TIME.format(details.closedAt()), orUnknown(details.closedByName()),
+                details.note() == null ? "" : ": " + details.note()), NamedTextColor.GRAY));
+        }
+
+        long caseId = summary.id();
+        UUID first = summary.first();
+        UUID second = summary.second();
+        CaseStatus status = summary.status();
+        List<String> shared = details.sharedNetworks();
+        List<DialogInput> inputs = new ArrayList<>();
+        List<ActionButton> buttons = new ArrayList<>();
+        if(status == CaseStatus.OPEN) {
+            inputs.add(noteInput("Notiz (optional)"));
+            for(Outcome outcome : Outcome.values())
+                buttons.add(inputButton("Schließen: " + outcome.label,
+                    (player, response) -> this.close(player, caseId, first, second, outcome, response.getText(NOTE_KEY))));
+        }
+        buttons.add(button(fullNetworks ? "Anschlüsse gekürzt" : "Volle Anschlüsse zeigen", player -> this.openCase(player, caseId, !fullNetworks)));
+        buttons.add(button("Accounts zu " + summary.firstName(), player -> this.openLinks(player, first)));
+        buttons.add(button("Accounts zu " + summary.secondName(), player -> this.openLinks(player, second)));
+        if(!shared.isEmpty()) buttons.add(button("IP-Ausnahme anlegen", player -> this.openNewExemption(player, shared)));
+        buttons.add(button("Zurück zur Liste", player -> this.openList(player, status)));
+        show(admin, "Verdachtsfall #" + caseId, lines(lines), inputs, buttons);
+    }
+
+    private void close(Player admin, long caseId, UUID first, UUID second, Outcome outcome, @Nullable String rawNote) {
+        String note = note(rawNote);
+        UUID adminUuid = admin.getUniqueId();
+        Instant now = Instant.now();
+        this.appliance.runFor(admin, connection -> {
+            this.repository.closeCase(connection, caseId, outcome, adminUuid, note, now);
+            if(outcome == Outcome.HOUSEHOLD) this.repository.linkHousehold(connection, List.of(first, second), adminUuid, note, now);
+        }, () -> {
+            Main.logger().info(String.format("BanEvasion: case #%d closed as %s by %s", caseId, outcome, admin.getName()));
+            admin.sendMessage(Component.text(String.format("Fall #%d geschlossen: %s", caseId, outcome.label), NamedTextColor.GRAY));
+            this.openList(admin, CaseStatus.OPEN);
+        });
+    }
+
+    private void createExemption(Player admin, List<String> allowed, DialogResponseView response) {
+        String network = response.getText(NETWORK_KEY);
+        Float hours = response.getFloat(HOURS_KEY);
+        if(network == null || !allowed.contains(network) || hours == null || hours < 1) {
+            admin.sendMessage(Component.text("Ungültige Eingabe.", NamedTextColor.RED));
+            return;
+        }
+        String note = note(response.getText(NOTE_KEY));
+        Instant from = Instant.now();
+        Instant until = from.plus(Duration.ofHours(Math.round(hours)));
+        UUID adminUuid = admin.getUniqueId();
+        this.appliance.runFor(admin, connection -> this.repository.addExemption(connection, network, from, until, adminUuid, note), () -> {
+            Main.logger().info(String.format("BanEvasion: exemption until %s added by %s", until, admin.getName()));
+            admin.sendMessage(Component.text(String.format("IP-Ausnahme für %s bis %s angelegt.", Networks.mask(network), TIME.format(until)), NamedTextColor.GRAY));
+        });
+    }
+
+    private void endExemption(Player admin, long exemptionId) {
+        Instant now = Instant.now();
+        this.appliance.runFor(admin, connection -> this.repository.endExemption(connection, exemptionId, now), () -> {
+            Main.logger().info(String.format("BanEvasion: exemption #%d ended by %s", exemptionId, admin.getName()));
+            this.openExemptions(admin);
+        });
+    }
+
+    private void removeMember(Player admin, long householdId, BanEvasionRepository.Member member) {
+        this.appliance.runFor(admin, connection -> this.repository.removeFromHousehold(connection, member.uuid()), () -> {
+            Main.logger().info(String.format("BanEvasion: %s removed from household #%d by %s", member.name(), householdId, admin.getName()));
+            this.openHousehold(admin, householdId);
+        });
+    }
+
+    private ActionButton backToList(String label) {
+        return button(label, player -> this.openList(player, CaseStatus.OPEN));
+    }
+
+    private static Component caseLabel(BanEvasionRepository.CaseSummary summary) {
+        NamedTextColor color = summary.severity() == Severity.HIGH ? NamedTextColor.RED : NamedTextColor.WHITE;
+        String outcome = summary.outcome() == null ? "" : " · " + summary.outcome().label;
+        return Component.text(String.format("#%d %s ↔ %s · %s%s",
+            summary.id(), summary.firstName(), summary.secondName(), TIME.format(summary.lastSeenAt()), outcome), color);
+    }
+
+    private static Component accountLine(String name, @Nullable BanState state, @Nullable Long household) {
+        String ban = switch(state == null ? BanState.UNKNOWN : state) {
+            case BANNED -> "gebannt";
+            case NOT_BANNED -> "nicht gebannt";
+            case UNKNOWN -> "Bann-Status unbekannt";
+        };
+        String householdText = household == null ? "" : " · Haushalt #" + household;
+        return Component.text(name + " – " + ban + householdText, state == BanState.BANNED ? NamedTextColor.RED : NamedTextColor.WHITE);
+    }
+
+    private static String network(String network, boolean full) {
+        return full ? network : Networks.mask(network);
+    }
+
+    private static String networks(List<String> networks, boolean full) {
+        if(networks.isEmpty()) return "keine";
+        return networks.stream().map(network -> network(network, full)).collect(Collectors.joining(", "));
+    }
+
+    private static String orUnknown(@Nullable String name) {
+        return name == null ? "?" : name;
+    }
+
+    private static @Nullable String note(@Nullable String raw) {
+        return raw == null || raw.isBlank() ? null : raw.strip();
+    }
+
+    private static DialogInput noteInput(String label) {
+        return DialogInput.text(NOTE_KEY, Component.text(label)).width(BODY_WIDTH).maxLength(255).build();
+    }
+
+    private static Component lines(List<Component> lines) {
+        return Component.join(JoinConfiguration.newlines(), lines);
+    }
+
+    private static DialogAction adminAction(BiConsumer<Player, DialogResponseView> action) {
+        return DialogAction.customClick((response, audience) -> {
+            if(!(audience instanceof Player player)) return;
+            Bukkit.getScheduler().runTask(Main.instance(), () -> {
+                if(player.isOnline() && player.hasPermission(BanEvasion.ADMIN_PERMISSION)) action.accept(player, response);
+            });
+        }, DIALOG_CALLBACK);
+    }
+
+    private static ActionButton button(Component label, Consumer<Player> action) {
+        return ActionButton.builder(label).width(BUTTON_WIDTH).action(adminAction((player, response) -> action.accept(player))).build();
+    }
+
+    private static ActionButton button(String label, Consumer<Player> action) {
+        return button(Component.text(label), action);
+    }
+
+    /**
+     * Button that reads the inputs of the dialog.
+     */
+    private static ActionButton inputButton(String label, BiConsumer<Player, DialogResponseView> action) {
+        return ActionButton.builder(Component.text(label)).width(BUTTON_WIDTH).action(adminAction(action)).build();
+    }
+
+    private static void show(Player admin, String title, Component body, List<DialogInput> inputs, List<ActionButton> buttons) {
+        Dialog dialog = Dialog.create(factory -> factory.empty()
+            .base(DialogBase.builder(Component.text(title))
+                .canCloseWithEscape(true)
+                .afterAction(DialogBase.DialogAfterAction.CLOSE)
+                .body(List.of(DialogBody.plainMessage(body, BODY_WIDTH)))
+                .inputs(inputs)
+                .build())
+            .type(DialogType.multiAction(buttons)
+                .columns(1)
+                .exitAction(ActionButton.builder(Component.text("Schließen")).width(BUTTON_WIDTH).build())
+                .build()));
+        admin.showDialog(dialog);
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/BanEvasionListener.java

@@ -0,0 +1,24 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import eu.mhsl.craftattack.spawn.core.appliance.ApplianceListener;
+import eu.mhsl.craftattack.spawn.core.event.LoginAttemptRecordedEvent;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.player.PlayerQuitEvent;
+
+class BanEvasionListener extends ApplianceListener<BanEvasion> {
+    @EventHandler
+    public void onAttemptRecorded(LoginAttemptRecordedEvent event) {
+        this.getAppliance().onAttemptRecorded(event.getAttempt());
+    }
+
+    @EventHandler
+    public void onJoin(PlayerJoinEvent event) {
+        this.getAppliance().playerJoined(event.getPlayer());
+    }
+
+    @EventHandler
+    public void onQuit(PlayerQuitEvent event) {
+        this.getAppliance().playerLeft(event.getPlayer());
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/BanEvasionRepository.java

@@ -0,0 +1,504 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.ZoneOffset;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * All SQL of the ban evasion detection. Plain JDBC without Bukkit, every method runs on the caller's connection.
+ * Tables: resources/migrations/banEvasion, connection keys: login_attempts.network.
+ */
+final class BanEvasionRepository {
+    record CaseSummary(
+        long id,
+        UUID first,
+        String firstName,
+        UUID second,
+        String secondName,
+        CaseStatus status,
+        @Nullable Outcome outcome,
+        Severity severity,
+        Instant lastSeenAt,
+        int hits
+    ) {
+    }
+
+    record CaseReason(Reason reason, Severity severity, Instant firstSeenAt) {
+    }
+
+    record TimelineEntry(Instant at, String name, @Nullable String network, String stage, String result) {
+    }
+
+    record CaseDetails(
+        CaseSummary summary,
+        boolean banStatusUnknown,
+        Instant createdAt,
+        @Nullable Instant closedAt,
+        @Nullable String closedByName,
+        @Nullable String note,
+        List<CaseReason> reasons,
+        List<String> sharedNetworks,
+        List<TimelineEntry> timeline
+    ) {
+    }
+
+    record OpenCount(int total, int high) {
+    }
+
+    record Link(UUID uuid, String name, int sharedAttempts, Instant firstAt, Instant lastAt, @Nullable Long caseId) {
+    }
+
+    record Member(UUID uuid, String name) {
+    }
+
+    record Household(long id, Instant createdAt, @Nullable String createdByName, @Nullable String note, List<Member> members) {
+    }
+
+    record Exemption(long id, String network, Instant validFrom, Instant validUntil, @Nullable String createdByName, @Nullable String note) {
+    }
+
+    @FunctionalInterface
+    private interface RowMapper<T> {
+        T map(ResultSet row) throws SQLException;
+    }
+
+    /**
+     * Latest known name of the account in the given column.
+     */
+    private static final String NAME_OF = "(SELECT n.name FROM login_attempts n WHERE n.uuid = %s ORDER BY n.at DESC LIMIT 1)";
+
+    boolean isExempt(Connection connection, String network, Instant at) throws SQLException {
+        String sql = "SELECT 1 FROM ban_evasion_ip_exemptions WHERE network = ? AND ? BETWEEN valid_from AND valid_until LIMIT 1";
+        return first(connection, sql, row -> true, network, at) != null;
+    }
+
+    List<Attempt> partnerAttempts(Connection connection, Attempt current, Duration window) throws SQLException {
+        String sql = """
+            SELECT a.id, a.at, a.uuid, a.name, a.network, a.stage, a.result
+            FROM login_attempts a
+            WHERE a.network = ? AND a.uuid <> ? AND a.at BETWEEN ? AND ?
+              AND NOT EXISTS (
+                SELECT 1 FROM ban_evasion_ip_exemptions e
+                WHERE e.network = a.network AND a.at BETWEEN e.valid_from AND e.valid_until
+              )
+            ORDER BY a.at
+            """;
+        return list(connection, sql, row -> new Attempt(
+            row.getLong("id"),
+            fromDb(row, "at"),
+            uuid(row, "uuid"),
+            row.getString("name"),
+            row.getString("network"),
+            row.getString("stage"),
+            row.getString("result")
+        ), current.network(), current.uuid(), current.at().minus(window), current.at());
+    }
+
+    Map<UUID, Long> householdsOf(Connection connection, Collection<UUID> uuids) throws SQLException {
+        if(uuids.isEmpty()) return Map.of();
+        String sql = "SELECT uuid, household_id FROM ban_evasion_household_members WHERE uuid IN (" + placeholders(uuids.size()) + ")";
+        Map<UUID, Long> households = new HashMap<>();
+        list(connection, sql, row -> Map.entry(uuid(row, "uuid"), row.getLong("household_id")), uuids.toArray())
+            .forEach(entry -> households.put(entry.getKey(), entry.getValue()));
+        return households;
+    }
+
+    Map<Long, Set<UUID>> householdMembers(Connection connection, Collection<Long> householdIds) throws SQLException {
+        if(householdIds.isEmpty()) return Map.of();
+        String sql = "SELECT household_id, uuid FROM ban_evasion_household_members WHERE household_id IN (" + placeholders(householdIds.size()) + ")";
+        Map<Long, Set<UUID>> members = new HashMap<>();
+        list(connection, sql, row -> Map.entry(row.getLong("household_id"), uuid(row, "uuid")), householdIds.toArray())
+            .forEach(entry -> members.computeIfAbsent(entry.getKey(), id -> new HashSet<>()).add(entry.getValue()));
+        return members;
+    }
+
+    @Nullable CaseDecision.ExistingCase findCase(Connection connection, UUID first, UUID second) throws SQLException {
+        String sql = "SELECT id, status, outcome FROM ban_evasion_cases WHERE uuid_a = ? AND uuid_b = ?";
+        CaseDecision.ExistingCase found = first(connection, sql, row -> new CaseDecision.ExistingCase(
+            row.getLong("id"), CaseStatus.valueOf(row.getString("status")), outcomeOf(row), EnumSet.noneOf(Reason.class)
+        ), first, second);
+        if(found == null) return null;
+        this.reasonsOf(connection, found.id()).forEach(reason -> found.reasons().add(reason.reason()));
+        return found;
+    }
+
+    /**
+     * Creates the case, or returns the id of the existing case of the pair.
+     */
+    long createCase(Connection connection, PairFinding finding, Instant at) throws SQLException {
+        String sql = """
+            INSERT INTO ban_evasion_cases (uuid_a, uuid_b, status, severity, ban_status_unknown, created_at, last_seen_at, hits)
+            VALUES (?, ?, 'OPEN', ?, ?, ?, ?, 1)
+            ON DUPLICATE KEY UPDATE id = LAST_INSERT_ID(id)
+            """;
+        return insert(connection, sql, finding.first(), finding.second(), finding.severity(), finding.banStatusUnknown(), at, at);
+    }
+
+    void updateCase(Connection connection, long caseId, PairFinding finding, Instant at, boolean reopen) throws SQLException {
+        String sql = """
+            UPDATE ban_evasion_cases SET
+                last_seen_at = GREATEST(last_seen_at, ?),
+                hits = hits + 1,
+                severity = IF(severity = 'HIGH' OR ? = 'HIGH', 'HIGH', 'NORMAL'),
+                ban_status_unknown = ?,
+                status = IF(?, 'OPEN', status),
+                outcome = IF(?, NULL, outcome)
+            WHERE id = ?
+            """;
+        update(connection, sql, at, finding.severity(), finding.banStatusUnknown(), reopen, reopen, caseId);
+    }
+
+    void addReasons(Connection connection, long caseId, Map<Reason, Severity> reasons, Set<Reason> which, long attemptId, Instant at) throws SQLException {
+        String sql = "INSERT IGNORE INTO ban_evasion_case_reasons (case_id, reason, severity, first_seen_at, attempt_id) VALUES (?, ?, ?, ?, ?)";
+        for(Reason reason : which) update(connection, sql, caseId, reason, reasons.get(reason), at, attemptId);
+    }
+
+    List<CaseSummary> listCases(Connection connection, CaseStatus status, int limit) throws SQLException {
+        String sql = """
+            SELECT c.id, c.uuid_a, c.uuid_b, c.status, c.outcome, c.severity, c.last_seen_at, c.hits,
+                   %s AS name_a, %s AS name_b
+            FROM ban_evasion_cases c
+            WHERE c.status = ?
+            ORDER BY c.severity = 'HIGH' DESC, c.last_seen_at DESC
+            LIMIT ?
+            """.formatted(NAME_OF.formatted("c.uuid_a"), NAME_OF.formatted("c.uuid_b"));
+        return list(connection, sql, BanEvasionRepository::summaryOf, status, limit);
+    }
+
+    OpenCount countOpen(Connection connection) throws SQLException {
+        String sql = "SELECT COUNT(*) AS total, COALESCE(SUM(severity = 'HIGH'), 0) AS high FROM ban_evasion_cases WHERE status = 'OPEN'";
+        return Objects.requireNonNull(first(connection, sql, row -> new OpenCount(row.getInt("total"), row.getInt("high"))));
+    }
+
+    @Nullable CaseDetails loadCase(Connection connection, long caseId, int timelineLimit) throws SQLException {
+        String sql = """
+            SELECT c.*, %s AS name_a, %s AS name_b, %s AS closed_by_name
+            FROM ban_evasion_cases c
+            WHERE c.id = ?
+            """.formatted(NAME_OF.formatted("c.uuid_a"), NAME_OF.formatted("c.uuid_b"), NAME_OF.formatted("c.closed_by"));
+        CaseDetails found = first(connection, sql, row -> new CaseDetails(
+            summaryOf(row),
+            row.getBoolean("ban_status_unknown"),
+            fromDb(row, "created_at"),
+            nullableFromDb(row, "closed_at"),
+            row.getString("closed_by_name"),
+            row.getString("note"),
+            List.of(), List.of(), List.of()
+        ), caseId);
+        if(found == null) return null;
+        UUID first = found.summary().first();
+        UUID second = found.summary().second();
+        return new CaseDetails(
+            found.summary(), found.banStatusUnknown(), found.createdAt(), found.closedAt(), found.closedByName(), found.note(),
+            this.reasonsOf(connection, caseId),
+            this.sharedNetworks(connection, first, second),
+            this.timeline(connection, first, second, timelineLimit)
+        );
+    }
+
+    void closeCase(Connection connection, long caseId, Outcome outcome, UUID admin, @Nullable String note, Instant at) throws SQLException {
+        String sql = "UPDATE ban_evasion_cases SET status = 'CLOSED', outcome = ?, closed_at = ?, closed_by = ?, note = ? WHERE id = ?";
+        update(connection, sql, outcome, at, admin, note, caseId);
+    }
+
+    /**
+     * All accounts that ever used one of the connections of the given account, most recent first.
+     */
+    List<Link> linksOf(Connection connection, UUID uuid, int limit) throws SQLException {
+        String sql = """
+            SELECT o.uuid, %s AS name, COUNT(*) AS shared, MIN(o.at) AS first_at, MAX(o.at) AS last_at,
+                   (SELECT c.id FROM ban_evasion_cases c
+                    WHERE (c.uuid_a = ? AND c.uuid_b = o.uuid) OR (c.uuid_a = o.uuid AND c.uuid_b = ?)) AS case_id
+            FROM login_attempts o
+            WHERE o.uuid <> ? AND o.network IN (
+                SELECT s.network FROM login_attempts s WHERE s.uuid = ? AND s.network IS NOT NULL
+            )
+            GROUP BY o.uuid
+            ORDER BY last_at DESC
+            LIMIT ?
+            """.formatted(NAME_OF.formatted("o.uuid"));
+        return list(connection, sql, row -> {
+            UUID other = uuid(row, "uuid");
+            return new Link(
+                other,
+                nameOr(row.getString("name"), other),
+                row.getInt("shared"),
+                fromDb(row, "first_at"),
+                fromDb(row, "last_at"),
+                row.getObject("case_id", Long.class)
+            );
+        }, uuid, uuid, uuid, uuid, limit);
+    }
+
+    /**
+     * Latest account that used the name (case-insensitive), with its name as stored.
+     */
+    @Nullable Member accountByName(Connection connection, String name) throws SQLException {
+        String sql = "SELECT uuid, name FROM login_attempts WHERE name = ? ORDER BY at DESC LIMIT 1";
+        return first(connection, sql, row -> new Member(uuid(row, "uuid"), row.getString("name")), name);
+    }
+
+    String nameOf(Connection connection, UUID uuid) throws SQLException {
+        String name = first(connection, "SELECT name FROM login_attempts WHERE uuid = ? ORDER BY at DESC LIMIT 1", row -> row.getString("name"), uuid);
+        return nameOr(name, uuid);
+    }
+
+    List<String> recentNetworks(Connection connection, UUID uuid, int limit) throws SQLException {
+        String sql = """
+            SELECT network, MAX(at) AS last_at FROM login_attempts
+            WHERE uuid = ? AND network IS NOT NULL
+            GROUP BY network ORDER BY last_at DESC LIMIT ?
+            """;
+        return list(connection, sql, row -> row.getString("network"), uuid, limit);
+    }
+
+    void addExemption(Connection connection, String network, Instant from, Instant until, UUID admin, @Nullable String note) throws SQLException {
+        String sql = "INSERT INTO ban_evasion_ip_exemptions (network, valid_from, valid_until, created_by, note) VALUES (?, ?, ?, ?, ?)";
+        update(connection, sql, network, from, until, admin, note);
+    }
+
+    List<Exemption> activeExemptions(Connection connection, Instant now) throws SQLException {
+        String sql = """
+            SELECT e.id, e.network, e.valid_from, e.valid_until, e.note, %s AS created_by_name
+            FROM ban_evasion_ip_exemptions e
+            WHERE e.valid_until >= ?
+            ORDER BY e.valid_until
+            """.formatted(NAME_OF.formatted("e.created_by"));
+        return list(connection, sql, row -> new Exemption(
+            row.getLong("id"),
+            row.getString("network"),
+            fromDb(row, "valid_from"),
+            fromDb(row, "valid_until"),
+            row.getString("created_by_name"),
+            row.getString("note")
+        ), now);
+    }
+
+    void endExemption(Connection connection, long id, Instant now) throws SQLException {
+        update(connection, "UPDATE ban_evasion_ip_exemptions SET valid_until = ? WHERE id = ? AND valid_until > ?", now, id, now);
+    }
+
+    /**
+     * Puts the accounts into one household; existing households of these accounts are merged.
+     */
+    void linkHousehold(Connection connection, Collection<UUID> uuids, UUID admin, @Nullable String note, Instant at) throws SQLException {
+        boolean autoCommit = connection.getAutoCommit();
+        connection.setAutoCommit(false);
+        try {
+            List<Long> existing = this.householdsOf(connection, uuids).values().stream().distinct().sorted().toList();
+            long target = existing.isEmpty()
+                ? insert(connection, "INSERT INTO ban_evasion_households (created_at, created_by, note) VALUES (?, ?, ?)", at, admin, note)
+                : existing.getFirst();
+            if(existing.size() > 1) {
+                Object[] merged = existing.subList(1, existing.size()).toArray();
+                String in = placeholders(merged.length);
+                Object[] moveParams = new Object[merged.length + 1];
+                moveParams[0] = target;
+                System.arraycopy(merged, 0, moveParams, 1, merged.length);
+                update(connection, "UPDATE ban_evasion_household_members SET household_id = ? WHERE household_id IN (" + in + ")", moveParams);
+                update(connection, "DELETE FROM ban_evasion_households WHERE id IN (" + in + ")", merged);
+            }
+            for(UUID uuid : uuids)
+                update(connection, "INSERT IGNORE INTO ban_evasion_household_members (uuid, household_id) VALUES (?, ?)", uuid, target);
+            connection.commit();
+        } catch(SQLException | RuntimeException e) {
+            connection.rollback();
+            throw e;
+        } finally {
+            connection.setAutoCommit(autoCommit);
+        }
+    }
+
+    /**
+     * All households, newest first.
+     */
+    List<Household> listHouseholds(Connection connection) throws SQLException {
+        return this.households(connection, "");
+    }
+
+    @Nullable Household household(Connection connection, long id) throws SQLException {
+        List<Household> households = this.households(connection, "WHERE h.id = ?", id);
+        return households.isEmpty() ? null : households.getFirst();
+    }
+
+    private List<Household> households(Connection connection, String where, Object... params) throws SQLException {
+        String sql = """
+            SELECT h.id, h.created_at, h.note, %s AS created_by_name, m.uuid, %s AS name
+            FROM ban_evasion_households h
+            JOIN ban_evasion_household_members m ON m.household_id = h.id
+            %s
+            ORDER BY h.id DESC, name
+            """.formatted(NAME_OF.formatted("h.created_by"), NAME_OF.formatted("m.uuid"), where);
+        Map<Long, Household> households = new LinkedHashMap<>();
+        list(connection, sql, row -> {
+            UUID uuid = uuid(row, "uuid");
+            Household household = households.get(row.getLong("id"));
+            if(household == null) {
+                household = new Household(row.getLong("id"), fromDb(row, "created_at"), row.getString("created_by_name"), row.getString("note"), new ArrayList<>());
+                households.put(household.id(), household);
+            }
+            return household.members().add(new Member(uuid, nameOr(row.getString("name"), uuid)));
+        }, params);
+        return List.copyOf(households.values());
+    }
+
+    /**
+     * Removes the account from its household; a household with fewer than two members is dissolved.
+     */
+    void removeFromHousehold(Connection connection, UUID uuid) throws SQLException {
+        Long household = this.householdsOf(connection, List.of(uuid)).get(uuid);
+        if(household == null) return;
+        update(connection, "DELETE FROM ban_evasion_household_members WHERE uuid = ?", uuid);
+        update(connection,
+            "DELETE FROM ban_evasion_households WHERE id = ? AND (SELECT COUNT(*) FROM ban_evasion_household_members WHERE household_id = ?) < 2",
+            household, household);
+    }
+
+    int deleteExpired(Connection connection, int retentionMonths) throws SQLException {
+        return update(connection, "DELETE FROM ban_evasion_cases WHERE last_seen_at < UTC_TIMESTAMP() - INTERVAL ? MONTH", retentionMonths)
+            + update(connection, "DELETE FROM ban_evasion_ip_exemptions WHERE valid_until < UTC_TIMESTAMP() - INTERVAL ? MONTH", retentionMonths);
+    }
+
+    private List<CaseReason> reasonsOf(Connection connection, long caseId) throws SQLException {
+        String sql = "SELECT reason, severity, first_seen_at FROM ban_evasion_case_reasons WHERE case_id = ? ORDER BY first_seen_at, reason";
+        return list(connection, sql, row -> new CaseReason(
+            Reason.valueOf(row.getString("reason")),
+            Severity.valueOf(row.getString("severity")),
+            fromDb(row, "first_seen_at")
+        ), caseId);
+    }
+
+    private List<String> sharedNetworks(Connection connection, UUID first, UUID second) throws SQLException {
+        String sql = """
+            SELECT DISTINCT a.network FROM login_attempts a
+            WHERE a.uuid = ? AND a.network IS NOT NULL
+              AND EXISTS (SELECT 1 FROM login_attempts b WHERE b.uuid = ? AND b.network = a.network)
+            ORDER BY a.network
+            """;
+        return list(connection, sql, row -> row.getString("network"), first, second);
+    }
+
+    private List<TimelineEntry> timeline(Connection connection, UUID first, UUID second, int limit) throws SQLException {
+        String sql = "SELECT at, name, network, stage, result FROM login_attempts WHERE uuid IN (?, ?) ORDER BY at DESC LIMIT ?";
+        return list(connection, sql, row -> new TimelineEntry(
+            fromDb(row, "at"), row.getString("name"), row.getString("network"), row.getString("stage"), row.getString("result")
+        ), first, second, limit);
+    }
+
+    private static CaseSummary summaryOf(ResultSet row) throws SQLException {
+        UUID first = uuid(row, "uuid_a");
+        UUID second = uuid(row, "uuid_b");
+        return new CaseSummary(
+            row.getLong("id"),
+            first,
+            nameOr(row.getString("name_a"), first),
+            second,
+            nameOr(row.getString("name_b"), second),
+            CaseStatus.valueOf(row.getString("status")),
+            outcomeOf(row),
+            Severity.valueOf(row.getString("severity")),
+            fromDb(row, "last_seen_at"),
+            row.getInt("hits")
+        );
+    }
+
+    private static <T> List<T> list(Connection connection, String sql, RowMapper<T> mapper, Object... params) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            bind(statement, params);
+            List<T> rows = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) rows.add(mapper.map(row));
+            }
+            return rows;
+        }
+    }
+
+    private static <T> @Nullable T first(Connection connection, String sql, RowMapper<T> mapper, Object... params) throws SQLException {
+        List<T> rows = list(connection, sql, mapper, params);
+        return rows.isEmpty() ? null : rows.getFirst();
+    }
+
+    private static int update(Connection connection, String sql, Object... params) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            bind(statement, params);
+            return statement.executeUpdate();
+        }
+    }
+
+    /**
+     * Executes an insert and returns the generated (or, with LAST_INSERT_ID(id), the existing) id.
+     */
+    private static long insert(Connection connection, String sql, Object... params) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
+            bind(statement, params);
+            statement.executeUpdate();
+            try(ResultSet keys = statement.getGeneratedKeys()) {
+                if(!keys.next()) throw new SQLException("no id returned by insert");
+                return keys.getLong(1);
+            }
+        }
+    }
+
+    private static void bind(PreparedStatement statement, Object... params) throws SQLException {
+        for(int i = 0; i < params.length; i++) {
+            Object value = switch(params[i]) {
+                case UUID uuid -> uuid.toString();
+                case Instant instant -> toDb(instant);
+                case Enum<?> constant -> constant.name();
+                case null -> null;
+                default -> params[i];
+            };
+            statement.setObject(i + 1, value);
+        }
+    }
+
+    private static UUID uuid(ResultSet row, String column) throws SQLException {
+        return UUID.fromString(row.getString(column));
+    }
+
+    private static @Nullable Outcome outcomeOf(ResultSet row) throws SQLException {
+        String outcome = row.getString("outcome");
+        return outcome == null ? null : Outcome.valueOf(outcome);
+    }
+
+    private static String nameOr(@Nullable String name, UUID uuid) {
+        return name != null ? name : uuid.toString();
+    }
+
+    private static String placeholders(int count) {
+        return String.join(", ", Collections.nCopies(count, "?"));
+    }
+
+    private static LocalDateTime toDb(Instant instant) {
+        return LocalDateTime.ofInstant(instant, ZoneOffset.UTC);
+    }
+
+    private static Instant fromDb(ResultSet row, String column) throws SQLException {
+        return Objects.requireNonNull(nullableFromDb(row, column), column);
+    }
+
+    private static @Nullable Instant nullableFromDb(ResultSet row, String column) throws SQLException {
+        LocalDateTime value = row.getObject(column, LocalDateTime.class);
+        return value == null ? null : value.toInstant(ZoneOffset.UTC);
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/BanState.java

@@ -0,0 +1,10 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+enum BanState {
+    BANNED,
+    NOT_BANNED,
+    /**
+     * The website API could not be asked.
+     */
+    UNKNOWN
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/BanStatusCache.java

@@ -0,0 +1,54 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Collection;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+
+/**
+ * Ban states from the website, kept for a short time. UNKNOWN (API unreachable) is never cached,
+ * but after a failure the website is not asked again for the backoff period, so an unreachable website
+ * does not slow down every evaluation. The lookup blocks (HTTP), so never call this on the main or database thread.
+ */
+final class BanStatusCache {
+    private record Entry(BanState state, Instant fetchedAt) {
+    }
+
+    private final Map<UUID, Entry> entries = new ConcurrentHashMap<>();
+    private final Function<UUID, BanState> lookup;
+    private final Duration ttl;
+    private final Duration backoff;
+    private final Clock clock;
+    private volatile Instant failingUntil = Instant.MIN;
+
+    BanStatusCache(Function<UUID, BanState> lookup, Duration ttl, Duration backoff, Clock clock) {
+        this.lookup = lookup;
+        this.ttl = ttl;
+        this.backoff = backoff;
+        this.clock = clock;
+    }
+
+    BanState get(UUID uuid) {
+        Instant now = this.clock.instant();
+        Entry entry = this.entries.get(uuid);
+        if(entry != null && entry.fetchedAt().plus(this.ttl).isAfter(now)) return entry.state();
+
+        if(now.isBefore(this.failingUntil)) return BanState.UNKNOWN;
+
+        BanState state = this.lookup.apply(uuid);
+        if(state == BanState.UNKNOWN) this.failingUntil = this.clock.instant().plus(this.backoff);
+        else this.entries.put(uuid, new Entry(state, now));
+        return state;
+    }
+
+    Map<UUID, BanState> getAll(Collection<UUID> uuids) {
+        Map<UUID, BanState> states = new LinkedHashMap<>();
+        uuids.forEach(uuid -> states.put(uuid, this.get(uuid)));
+        return states;
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/CaseDecision.java

@@ -0,0 +1,42 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.util.EnumSet;
+import java.util.Set;
+
+/**
+ * Deduplication: one case per pair; admins are only notified about new information.
+ * A closed case reopens only for a new reason of severity HIGH, a case closed as confirmed evasion never:
+ * further attempts of the banned person are expected there and only recorded.
+ */
+final class CaseDecision {
+    record ExistingCase(long id, CaseStatus status, @Nullable Outcome outcome, Set<Reason> reasons) {
+    }
+
+    /**
+     * @param newReasons reasons not yet recorded for the case (all reasons for a new case)
+     */
+    record Result(boolean reopen, Set<Reason> newReasons, boolean announce) {
+    }
+
+    private CaseDecision() {
+    }
+
+    static Result decide(@Nullable ExistingCase existing, PairFinding finding) {
+        if(existing == null) return new Result(false, Set.copyOf(finding.reasons().keySet()), true);
+
+        Set<Reason> newReasons = EnumSet.noneOf(Reason.class);
+        finding.reasons().keySet().stream()
+            .filter(reason -> !existing.reasons().contains(reason))
+            .forEach(newReasons::add);
+
+        boolean newRelevant = newReasons.stream().anyMatch(reason -> !reason.informational);
+        boolean newHigh = newReasons.stream()
+            .anyMatch(reason -> !reason.informational && finding.reasons().get(reason) == Severity.HIGH);
+
+        if(existing.status() == CaseStatus.OPEN) return new Result(false, newReasons, newRelevant);
+        if(existing.outcome() == Outcome.CONFIRMED) return new Result(false, newReasons, false);
+        return new Result(newHigh, newReasons, newHigh);
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/CaseEvaluator.java

@@ -0,0 +1,97 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.EnumMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * Rules of the ban evasion detection, free of Bukkit and database access.
+ * Judges one new login attempt against all attempts of other accounts from the same connection.
+ */
+final class CaseEvaluator {
+    /**
+     * @param partnerAttempts     attempts of other accounts from the same connection within the time window, not exempted
+     * @param banStates           ban state of the current account, its partners and all members of their households
+     * @param households          household id per account, only for accounts in a household
+     * @param householdMembers    members per household id
+     * @param onlineOnSameNetwork accounts currently online from the same connection
+     */
+    record Input(
+        Attempt current,
+        List<Attempt> partnerAttempts,
+        Map<UUID, BanState> banStates,
+        Map<UUID, Long> households,
+        Map<Long, Set<UUID>> householdMembers,
+        Set<UUID> onlineOnSameNetwork,
+        Duration rejectionWindow
+    ) {
+    }
+
+    private CaseEvaluator() {
+    }
+
+    static List<PairFinding> evaluate(Input input) {
+        UUID self = input.current().uuid();
+        Map<UUID, List<Attempt>> byPartner = new LinkedHashMap<>();
+        input.partnerAttempts().stream()
+            .filter(attempt -> !attempt.uuid().equals(self))
+            .forEach(attempt -> byPartner.computeIfAbsent(attempt.uuid(), uuid -> new ArrayList<>()).add(attempt));
+
+        List<PairFinding> findings = new ArrayList<>();
+        byPartner.forEach((partner, attempts) -> {
+            PairFinding finding = evaluatePair(input, partner, attempts);
+            if(finding != null) findings.add(finding);
+        });
+        return findings;
+    }
+
+    private static @Nullable PairFinding evaluatePair(Input input, UUID partner, List<Attempt> partnerAttempts) {
+        Attempt current = input.current();
+        BanState selfState = banState(input, current.uuid());
+        BanState partnerState = banState(input, partner);
+
+        Long household = input.households().get(current.uuid());
+        boolean sameHousehold = household != null && household.equals(input.households().get(partner));
+        if(sameHousehold && !householdBanned(input, household)) return null;
+
+        Map<Reason, Severity> reasons = new EnumMap<>(Reason.class);
+        reasons.put(Reason.SHARED_CONNECTION, Severity.NORMAL);
+        if(selfState == BanState.BANNED || partnerState == BanState.BANNED)
+            reasons.put(Reason.BANNED, Severity.HIGH);
+
+        Instant rejectionStart = current.at().minus(input.rejectionWindow());
+        boolean partnerRejectedRecently = partnerAttempts.stream()
+            .anyMatch(attempt -> attempt.isRejection()
+                && !attempt.at().isBefore(rejectionStart)
+                && !attempt.at().isAfter(current.at()));
+        if(partnerState == BanState.BANNED && partnerRejectedRecently)
+            reasons.put(Reason.AFTER_REJECTION, Severity.HIGH);
+
+        if(current.isWebsiteSignup())
+            reasons.put(Reason.WEBSITE_SIGNUP, partnerState == BanState.BANNED ? Severity.HIGH : Severity.NORMAL);
+        if(sameHousehold)
+            reasons.put(Reason.HOUSEHOLD_MEMBER_BANNED, Severity.HIGH);
+        if(input.onlineOnSameNetwork().contains(partner))
+            reasons.put(Reason.ONLINE_SIMULTANEOUSLY, Severity.NORMAL);
+
+        boolean unknown = selfState == BanState.UNKNOWN || partnerState == BanState.UNKNOWN;
+        return PairFinding.of(current.uuid(), partner, reasons, unknown);
+    }
+
+    private static BanState banState(Input input, UUID uuid) {
+        return input.banStates().getOrDefault(uuid, BanState.UNKNOWN);
+    }
+
+    private static boolean householdBanned(Input input, long household) {
+        return input.householdMembers().getOrDefault(household, Set.of()).stream()
+            .anyMatch(member -> banState(input, member) == BanState.BANNED);
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/CaseStatus.java

@@ -0,0 +1,6 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+enum CaseStatus {
+    OPEN,
+    CLOSED
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/OnlineNetworks.java

@@ -0,0 +1,32 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Collectors;
+
+/**
+ * Connection key of every online player, readable from any thread.
+ */
+final class OnlineNetworks {
+    private final Map<UUID, String> networks = new ConcurrentHashMap<>();
+
+    void joined(UUID uuid, @Nullable String network) {
+        if(network == null) this.networks.remove(uuid);
+        else this.networks.put(uuid, network);
+    }
+
+    void left(UUID uuid) {
+        this.networks.remove(uuid);
+    }
+
+    Set<UUID> onlineOn(String network) {
+        return this.networks.entrySet().stream()
+            .filter(entry -> entry.getValue().equals(network))
+            .map(Map.Entry::getKey)
+            .collect(Collectors.toUnmodifiableSet());
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/Outcome.java

@@ -0,0 +1,13 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+enum Outcome {
+    CONFIRMED("Umgehung bestätigt"),
+    UNFOUNDED("unbegründet"),
+    HOUSEHOLD("Haushalt");
+
+    final String label;
+
+    Outcome(String label) {
+        this.label = label;
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/PairFinding.java

@@ -0,0 +1,26 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+import java.util.Collections;
+import java.util.EnumMap;
+import java.util.Map;
+import java.util.UUID;
+
+/**
+ * Reasons why two accounts may belong to the same person. The pair is ordered by the textual UUID,
+ * so (a, b) and (b, a) always map to the same case.
+ */
+record PairFinding(UUID first, UUID second, Map<Reason, Severity> reasons, boolean banStatusUnknown) {
+    static PairFinding of(UUID x, UUID y, Map<Reason, Severity> reasons, boolean banStatusUnknown) {
+        boolean ordered = x.toString().compareTo(y.toString()) < 0;
+        EnumMap<Reason, Severity> copy = new EnumMap<>(Reason.class);
+        copy.putAll(reasons);
+        return new PairFinding(ordered ? x : y, ordered ? y : x, Collections.unmodifiableMap(copy), banStatusUnknown);
+    }
+
+    Severity severity() {
+        return this.reasons.entrySet().stream()
+            .filter(entry -> !entry.getKey().informational)
+            .map(Map.Entry::getValue)
+            .reduce(Severity.NORMAL, Severity::max);
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/Reason.java

@@ -0,0 +1,21 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+enum Reason {
+    SHARED_CONNECTION("gemeinsamer Anschluss", false),
+    BANNED("gebannt", false),
+    AFTER_REJECTION("nach Abweisung", false),
+    WEBSITE_SIGNUP("Webseiten-Anmeldung", false),
+    HOUSEHOLD_MEMBER_BANNED("Haushalt, Mitglied gebannt", false),
+    ONLINE_SIMULTANEOUSLY("gleichzeitig online", true);
+
+    final String label;
+    /**
+     * Informational reasons are shown in the case, but never trigger a notification.
+     */
+    final boolean informational;
+
+    Reason(String label, boolean informational) {
+        this.label = label;
+        this.informational = informational;
+    }
+}

craftattack/src/main/java/eu/mhsl/craftattack/spawn/craftattack/appliances/tooling/banEvasion/Severity.java

@@ -0,0 +1,16 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+enum Severity {
+    NORMAL("normal"),
+    HIGH("hoch");
+
+    final String label;
+
+    Severity(String label) {
+        this.label = label;
+    }
+
+    static Severity max(Severity a, Severity b) {
+        return a.compareTo(b) >= 0 ? a : b;
+    }
+}

craftattack/src/main/resources/migrations/banEvasion/001_create_tables.sql

@@ -0,0 +1,55 @@
+-- Suspected ban evasion: one case per pair of accounts that shared an internet connection.
+CREATE TABLE ban_evasion_cases (
+    id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+    uuid_a CHAR(36) NOT NULL COMMENT 'textually smaller UUID of the pair',
+    uuid_b CHAR(36) NOT NULL,
+    status VARCHAR(16) NOT NULL COMMENT 'OPEN or CLOSED',
+    outcome VARCHAR(16) NULL COMMENT 'CONFIRMED, UNFOUNDED or HOUSEHOLD once closed',
+    severity VARCHAR(16) NOT NULL COMMENT 'NORMAL or HIGH',
+    ban_status_unknown BOOLEAN NOT NULL DEFAULT FALSE COMMENT 'website API unreachable at the last evaluation',
+    created_at DATETIME(3) NOT NULL COMMENT 'UTC',
+    last_seen_at DATETIME(3) NOT NULL COMMENT 'UTC',
+    hits INT UNSIGNED NOT NULL DEFAULT 1,
+    closed_at DATETIME(3) NULL COMMENT 'UTC',
+    closed_by CHAR(36) NULL,
+    note VARCHAR(255) NULL,
+    UNIQUE KEY uq_pair (uuid_a, uuid_b),
+    KEY idx_uuid_b (uuid_b),
+    KEY idx_status (status, last_seen_at)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+CREATE TABLE ban_evasion_case_reasons (
+    case_id BIGINT UNSIGNED NOT NULL,
+    reason VARCHAR(32) NOT NULL,
+    severity VARCHAR(16) NOT NULL,
+    first_seen_at DATETIME(3) NOT NULL COMMENT 'UTC',
+    attempt_id BIGINT UNSIGNED NOT NULL COMMENT 'login_attempts.id that first produced the reason',
+    PRIMARY KEY (case_id, reason),
+    CONSTRAINT fk_reason_case FOREIGN KEY (case_id) REFERENCES ban_evasion_cases (id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+-- Accounts marked by admins as one household (siblings, ...): no reports among them unless a member is banned.
+CREATE TABLE ban_evasion_households (
+    id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+    created_at DATETIME(3) NOT NULL COMMENT 'UTC',
+    created_by CHAR(36) NOT NULL,
+    note VARCHAR(255) NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+CREATE TABLE ban_evasion_household_members (
+    uuid CHAR(36) NOT NULL PRIMARY KEY COMMENT 'an account belongs to at most one household',
+    household_id BIGINT UNSIGNED NOT NULL,
+    KEY idx_household (household_id),
+    CONSTRAINT fk_member_household FOREIGN KEY (household_id) REFERENCES ban_evasion_households (id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+-- Temporary exemptions of a connection (LAN party, ...): attempts within the period are not evaluated.
+CREATE TABLE ban_evasion_ip_exemptions (
+    id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+    network VARCHAR(45) NOT NULL COMMENT 'same format as login_attempts.network',
+    valid_from DATETIME(3) NOT NULL COMMENT 'UTC',
+    valid_until DATETIME(3) NOT NULL COMMENT 'UTC',
+    created_by CHAR(36) NOT NULL,
+    note VARCHAR(255) NULL,
+    KEY idx_network (network, valid_until)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;