added BanEvasion appliance

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

@@ -0,0 +1,35 @@
+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(!player.hasPermission(BanEvasion.ADMIN_PERMISSION)) return;
+        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 +1,77 @@
+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) {
+        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, notice.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 +1,22 @@
+package eu.mhsl.craftattack.spawn.craftattack.appliances.tooling.banEvasion;
+
+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) {
+    static final String STAGE_WEBSITE = "WEBSITE";
+
+    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 +1,272 @@
+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.Collection;
+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;
+
+    @FunctionalInterface
+    interface Loader<T> {
+        T load() throws Exception;
+    }
+
+    private record Households(Map<UUID, Long> ofAccount, Map<Long, Set<UUID>> members) {
+    }
+
+    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)), 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);
+            });
+        });
+    }
+
+    /**
+     * 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 = new Attempt(recorded.id(), recorded.at(), recorded.uuid(), recorded.name(), recorded.network(), recorded.stage(), recorded.result());
+        Set<UUID> online = this.onlineNetworks.onlineOn(recorded.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.loadFor(player, () -> this.query(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 {
+            if(this.query(connection -> this.repository.isExempt(connection, attempt.network(), attempt.at()))) return;
+            List<Attempt> partners = this.query(connection -> this.repository.partnerAttempts(connection, attempt, this.window));
+            if(partners.isEmpty()) return;
+
+            Set<UUID> involved = new HashSet<>();
+            involved.add(attempt.uuid());
+            partners.forEach(partner -> involved.add(partner.uuid()));
+            Households households = this.query(connection -> {
+                Map<UUID, Long> ofAccount = this.repository.householdsOf(connection, involved);
+                return new Households(ofAccount, this.repository.householdMembers(connection, new HashSet<>(ofAccount.values())));
+            });
+
+            Set<UUID> banStateNeeded = new HashSet<>(involved);
+            households.members().values().forEach(banStateNeeded::addAll);
+            Map<UUID, BanState> banStates = this.banStatus.getAll(banStateNeeded);
+
+            List<PairFinding> findings = CaseEvaluator.evaluate(new CaseEvaluator.Input(
+                attempt, partners, banStates, households.ofAccount(), households.members(), online, this.rejectionWindow
+            ));
+            for(PairFinding finding : findings) {
+                AdminNotifier.Notice notice = this.query(connection -> this.applyFinding(connection, finding, attempt, banStates));
+                if(notice != null) this.notifier.announce(notice);
+            }
+        } catch(Exception e) {
+            Main.logger().log(Level.WARNING, String.format("BanEvasion: evaluating login attempt #%d failed", attempt.id()), e);
+        }
+    }
+
+    private @Nullable AdminNotifier.Notice applyFinding(Connection connection, PairFinding finding, Attempt attempt, Map<UUID, BanState> banStates) 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,
+            this.repository.nameOf(connection, finding.first()),
+            banStates.get(finding.first()) == BanState.BANNED,
+            this.repository.nameOf(connection, 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);
+            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 +1,367 @@
+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.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.
+ */
+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 Duration CALLBACK_LIFETIME = Duration.ofHours(12);
+    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) {
+    }
+
+    private final BanEvasion appliance;
+
+    BanEvasionDialogs(BanEvasion appliance) {
+        this.appliance = appliance;
+    }
+
+    /**
+     * 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);
+            },
+            ClickCallback.Options.builder().uses(ClickCallback.UNLIMITED_USES).lifetime(CALLBACK_LIFETIME).build()
+        );
+    }
+
+    void openList(Player admin, CaseStatus status) {
+        this.appliance.loadFor(admin,
+            () -> this.appliance.query(connection -> this.appliance.repository().listCases(connection, status, LIST_LIMIT)),
+            cases -> {
+                List<ActionButton> buttons = new ArrayList<>();
+                cases.forEach(summary -> buttons.add(button(caseLabel(summary), (player, response) -> this.openCase(player, summary.id(), 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, () -> {
+            BanEvasionRepository.CaseDetails details = this.appliance.query(connection -> this.appliance.repository().loadCase(connection, caseId, TIMELINE_LIMIT));
+            if(details == null) return null;
+            List<UUID> accounts = List.of(details.summary().first(), details.summary().second());
+            Map<UUID, Long> households = this.appliance.query(connection -> this.appliance.repository().householdsOf(connection, accounts));
+            return new CaseView(details, this.appliance.banStates(accounts), 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.loadFor(admin, () -> this.appliance.query(connection -> this.appliance.repository().uuidByName(connection, name)), uuid -> {
+            if(uuid == null) {
+                admin.sendMessage(Component.text("Keine Einträge zu " + name + ".", NamedTextColor.RED));
+                return;
+            }
+            this.openLinks(admin, uuid);
+        });
+    }
+
+    void openLinks(Player admin, UUID uuid) {
+        this.appliance.loadFor(admin, () -> this.appliance.query(connection -> new LinksView(
+            this.appliance.repository().nameOf(connection, uuid),
+            this.appliance.repository().linksOf(connection, uuid, LINK_LIMIT),
+            this.appliance.repository().recentNetworks(connection, uuid, RECENT_NETWORKS)
+        )), view -> {
+            List<Component> lines = new ArrayList<>();
+            if(view.links().isEmpty()) lines.add(Component.text("Kein anderer Account hat je einen Anschluss mit " + view.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<>();
+            view.links().stream()
+                .filter(link -> link.caseId() != null)
+                .forEach(link -> buttons.add(button("Fall #" + link.caseId() + ": " + link.name(), player -> this.openCase(player, link.caseId(), false))));
+            if(!view.networks().isEmpty())
+                buttons.add(button("IP-Ausnahme für Anschluss von " + view.name(), player -> this.openNewExemption(player, view.networks())));
+            buttons.add(button("Zur Fallliste", player -> this.openList(player, CaseStatus.OPEN)));
+            show(admin, "Accounts zu " + view.name(), lines(lines), List.of(), buttons);
+        });
+    }
+
+    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(),
+            DialogInput.text(NOTE_KEY, Component.text("Notiz, z. B. LAN-Party bei …")).width(BODY_WIDTH).maxLength(255).build()
+        );
+        List<ActionButton> buttons = List.of(
+            button(Component.text("Ausnahme anlegen"), (player, response) -> this.createExemption(player, networks, response)),
+            button("Abbrechen", player -> this.openList(player, CaseStatus.OPEN))
+        );
+        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.loadFor(admin, () -> this.appliance.query(connection -> this.appliance.repository().activeExemptions(connection, now)), exemptions -> {
+            List<Component> lines = new ArrayList<>();
+            if(exemptions.isEmpty()) lines.add(Component.text("Keine aktiven IP-Ausnahmen."));
+            exemptions.forEach(exemption -> lines.add(Component.text(String.format("%s · %s bis %s · %s%s",
+                exemption.network(), TIME.format(exemption.validFrom()), TIME.format(exemption.validUntil()),
+                exemption.createdByName() == null ? "?" : exemption.createdByName(),
+                exemption.note() == null ? "" : " · " + exemption.note()))));
+
+            List<ActionButton> buttons = new ArrayList<>();
+            exemptions.forEach(exemption -> buttons.add(button("Beenden: " + exemption.network(), player -> this.endExemption(player, exemption))));
+            buttons.add(button("Zur Fallliste", player -> this.openList(player, CaseStatus.OPEN)));
+            show(admin, "IP-Ausnahmen", lines(lines), List.of(), buttons);
+        });
+    }
+
+    void openHouseholds(Player admin) {
+        this.appliance.loadFor(admin, () -> this.appliance.query(this.appliance.repository()::listHouseholds), households -> {
+            List<Component> lines = new ArrayList<>();
+            if(households.isEmpty()) lines.add(Component.text("Keine Haushalte."));
+            households.forEach(household -> lines.add(Component.text(String.format("#%d: %s%s",
+                household.id(),
+                household.members().stream().map(BanEvasionRepository.Member::name).collect(Collectors.joining(", ")),
+                household.note() == null ? "" : " · " + household.note()))));
+
+            List<ActionButton> buttons = new ArrayList<>();
+            households.forEach(household -> household.members().forEach(member ->
+                buttons.add(button("Aus #" + household.id() + " entfernen: " + member.name(), player -> this.removeMember(player, member)))));
+            buttons.add(button("Zur Fallliste", player -> this.openList(player, CaseStatus.OPEN)));
+            show(admin, "Haushalte", lines(lines), List.of(), buttons);
+        });
+    }
+
+    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()),
+                details.closedByName() == null ? "?" : details.closedByName(),
+                details.note() == null ? "" : ": " + details.note()), NamedTextColor.GRAY));
+        }
+
+        long caseId = summary.id();
+        List<DialogInput> inputs = new ArrayList<>();
+        List<ActionButton> buttons = new ArrayList<>();
+        if(summary.status() == CaseStatus.OPEN) {
+            inputs.add(DialogInput.text(NOTE_KEY, Component.text("Notiz (optional)")).width(BODY_WIDTH).maxLength(255).build());
+            for(Outcome outcome : Outcome.values())
+                buttons.add(button(Component.text("Schließen: " + outcome.label), (player, response) -> this.close(player, summary, 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, summary.first())));
+        buttons.add(button("Accounts zu " + summary.secondName(), player -> this.openLinks(player, summary.second())));
+        if(!details.sharedNetworks().isEmpty())
+            buttons.add(button("IP-Ausnahme anlegen", player -> this.openNewExemption(player, details.sharedNetworks())));
+        buttons.add(button("Zurück zur Liste", player -> this.openList(player, summary.status())));
+        show(admin, "Verdachtsfall #" + caseId, lines(lines), inputs, buttons);
+    }
+
+    private void close(Player admin, BanEvasionRepository.CaseSummary summary, Outcome outcome, @Nullable String rawNote) {
+        String note = rawNote == null || rawNote.isBlank() ? null : rawNote.strip();
+        UUID adminUuid = admin.getUniqueId();
+        Instant now = Instant.now();
+        this.appliance.loadFor(admin, () -> this.appliance.query(connection -> {
+            this.appliance.repository().closeCase(connection, summary.id(), outcome, adminUuid, note, now);
+            if(outcome == Outcome.HOUSEHOLD)
+                this.appliance.repository().linkHousehold(connection, List.of(summary.first(), summary.second()), adminUuid, note, now);
+            return true;
+        }), done -> {
+            Main.logger().info(String.format("BanEvasion: case #%d closed as %s by %s", summary.id(), outcome, admin.getName()));
+            admin.sendMessage(Component.text(String.format("Fall #%d geschlossen: %s", summary.id(), 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 rawNote = response.getText(NOTE_KEY);
+        String note = rawNote == null || rawNote.isBlank() ? null : rawNote.strip();
+        Instant from = Instant.now();
+        Instant until = from.plus(Duration.ofHours(Math.round(hours)));
+        UUID adminUuid = admin.getUniqueId();
+        this.appliance.loadFor(admin, () -> this.appliance.query(connection -> {
+            this.appliance.repository().addExemption(connection, network, from, until, adminUuid, note);
+            return true;
+        }), done -> {
+            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, BanEvasionRepository.Exemption exemption) {
+        Instant now = Instant.now();
+        this.appliance.loadFor(admin, () -> this.appliance.query(connection -> {
+            this.appliance.repository().endExemption(connection, exemption.id(), now);
+            return true;
+        }), done -> {
+            Main.logger().info(String.format("BanEvasion: exemption #%d ended by %s", exemption.id(), admin.getName()));
+            this.openExemptions(admin);
+        });
+    }
+
+    private void removeMember(Player admin, BanEvasionRepository.Member member) {
+        this.appliance.loadFor(admin, () -> this.appliance.query(connection -> {
+            this.appliance.repository().removeFromHousehold(connection, member.uuid());
+            return true;
+        }), done -> {
+            Main.logger().info(String.format("BanEvasion: %s removed from household by %s", member.name(), admin.getName()));
+            this.openHouseholds(admin);
+        });
+    }
+
+    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 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);
+                });
+            },
+            ClickCallback.Options.builder().uses(ClickCallback.UNLIMITED_USES).lifetime(CALLBACK_LIFETIME).build()
+        );
+    }
+
+    private static ActionButton button(Component label, BiConsumer<Player, DialogResponseView> action) {
+        return ActionButton.builder(label).width(BUTTON_WIDTH).action(adminAction(action)).build();
+    }
+
+    private static ActionButton button(String label, Consumer<Player> action) {
+        return button(Component.text(label), (player, response) -> action.accept(player));
+    }
+
+    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 +1,615 @@
+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.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, @Nullable String note, List<Member> members) {
+    }
+
+    record Exemption(long id, String network, Instant validFrom, Instant validUntil, @Nullable String createdByName, @Nullable String note) {
+    }
+
+    /**
+     * 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";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, network);
+            statement.setObject(2, toDb(at));
+            try(ResultSet result = statement.executeQuery()) {
+                return result.next();
+            }
+        }
+    }
+
+    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
+            """;
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, current.network());
+            statement.setString(2, current.uuid().toString());
+            statement.setObject(3, toDb(current.at().minus(window)));
+            statement.setObject(4, toDb(current.at()));
+            List<Attempt> attempts = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) attempts.add(new Attempt(
+                    row.getLong("id"),
+                    fromDb(row, "at"),
+                    UUID.fromString(row.getString("uuid")),
+                    row.getString("name"),
+                    row.getString("network"),
+                    row.getString("stage"),
+                    row.getString("result")
+                ));
+            }
+            return attempts;
+        }
+    }
+
+    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()) + ")";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            int index = 1;
+            for(UUID uuid : uuids) statement.setString(index++, uuid.toString());
+            Map<UUID, Long> households = new HashMap<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) households.put(UUID.fromString(row.getString("uuid")), row.getLong("household_id"));
+            }
+            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()) + ")";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            int index = 1;
+            for(long id : householdIds) statement.setLong(index++, id);
+            Map<Long, Set<UUID>> members = new HashMap<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next())
+                    members.computeIfAbsent(row.getLong("household_id"), id -> new HashSet<>()).add(UUID.fromString(row.getString("uuid")));
+            }
+            return members;
+        }
+    }
+
+    @Nullable CaseDecision.ExistingCase findCase(Connection connection, UUID first, UUID second) throws SQLException {
+        long id;
+        CaseStatus status;
+        try(PreparedStatement statement = connection.prepareStatement("SELECT id, status FROM ban_evasion_cases WHERE uuid_a = ? AND uuid_b = ?")) {
+            statement.setString(1, first.toString());
+            statement.setString(2, second.toString());
+            try(ResultSet row = statement.executeQuery()) {
+                if(!row.next()) return null;
+                id = row.getLong("id");
+                status = CaseStatus.valueOf(row.getString("status"));
+            }
+        }
+        Set<Reason> reasons = EnumSet.noneOf(Reason.class);
+        this.reasonsOf(connection, id).forEach(reason -> reasons.add(reason.reason()));
+        return new CaseDecision.ExistingCase(id, status, reasons);
+    }
+
+    /**
+     * 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)
+            """;
+        try(PreparedStatement statement = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
+            statement.setString(1, finding.first().toString());
+            statement.setString(2, finding.second().toString());
+            statement.setString(3, finding.severity().name());
+            statement.setBoolean(4, finding.banStatusUnknown());
+            statement.setObject(5, toDb(at));
+            statement.setObject(6, toDb(at));
+            statement.executeUpdate();
+            try(ResultSet keys = statement.getGeneratedKeys()) {
+                if(!keys.next()) throw new SQLException("no id returned for ban evasion case");
+                return keys.getLong(1);
+            }
+        }
+    }
+
+    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 = ?
+            """;
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setObject(1, toDb(at));
+            statement.setString(2, finding.severity().name());
+            statement.setBoolean(3, finding.banStatusUnknown());
+            statement.setBoolean(4, reopen);
+            statement.setBoolean(5, reopen);
+            statement.setLong(6, caseId);
+            statement.executeUpdate();
+        }
+    }
+
+    void addReasons(Connection connection, long caseId, Map<Reason, Severity> reasons, Set<Reason> which, long attemptId, Instant at) throws SQLException {
+        if(which.isEmpty()) return;
+        String sql = "INSERT IGNORE INTO ban_evasion_case_reasons (case_id, reason, severity, first_seen_at, attempt_id) VALUES (?, ?, ?, ?, ?)";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            for(Reason reason : which) {
+                statement.setLong(1, caseId);
+                statement.setString(2, reason.name());
+                statement.setString(3, reasons.get(reason).name());
+                statement.setObject(4, toDb(at));
+                statement.setLong(5, attemptId);
+                statement.addBatch();
+            }
+            statement.executeBatch();
+        }
+    }
+
+    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"));
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, status.name());
+            statement.setInt(2, limit);
+            List<CaseSummary> cases = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) cases.add(summaryOf(row));
+            }
+            return cases;
+        }
+    }
+
+    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'";
+        try(PreparedStatement statement = connection.prepareStatement(sql); ResultSet row = statement.executeQuery()) {
+            row.next();
+            return 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"));
+        CaseSummary summary;
+        boolean banStatusUnknown;
+        Instant createdAt;
+        Instant closedAt;
+        String closedByName;
+        String note;
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setLong(1, caseId);
+            try(ResultSet row = statement.executeQuery()) {
+                if(!row.next()) return null;
+                summary = summaryOf(row);
+                banStatusUnknown = row.getBoolean("ban_status_unknown");
+                createdAt = fromDb(row, "created_at");
+                closedAt = nullableFromDb(row, "closed_at");
+                closedByName = row.getString("closed_by_name");
+                note = row.getString("note");
+            }
+        }
+        return new CaseDetails(
+            summary, banStatusUnknown, createdAt, closedAt, closedByName, note,
+            this.reasonsOf(connection, caseId),
+            this.sharedNetworks(connection, summary.first(), summary.second()),
+            this.timeline(connection, summary.first(), summary.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 = ?";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, outcome.name());
+            statement.setObject(2, toDb(at));
+            statement.setString(3, admin.toString());
+            statement.setString(4, note);
+            statement.setLong(5, caseId);
+            statement.executeUpdate();
+        }
+    }
+
+    /**
+     * 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"));
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            for(int index = 1; index <= 4; index++) statement.setString(index, uuid.toString());
+            statement.setInt(5, limit);
+            List<Link> links = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) {
+                    UUID other = UUID.fromString(row.getString("uuid"));
+                    String name = nameOr(row.getString("name"), other);
+                    int shared = row.getInt("shared");
+                    Instant firstAt = fromDb(row, "first_at");
+                    Instant lastAt = fromDb(row, "last_at");
+                    long caseId = row.getLong("case_id");
+                    boolean noCase = row.wasNull();
+                    links.add(new Link(other, name, shared, firstAt, lastAt, noCase ? null : caseId));
+                }
+            }
+            return links;
+        }
+    }
+
+
+    @Nullable UUID uuidByName(Connection connection, String name) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement("SELECT uuid FROM login_attempts WHERE name = ? ORDER BY at DESC LIMIT 1")) {
+            statement.setString(1, name);
+            try(ResultSet row = statement.executeQuery()) {
+                return row.next() ? UUID.fromString(row.getString("uuid")) : null;
+            }
+        }
+    }
+
+    String nameOf(Connection connection, UUID uuid) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement("SELECT name FROM login_attempts WHERE uuid = ? ORDER BY at DESC LIMIT 1")) {
+            statement.setString(1, uuid.toString());
+            try(ResultSet row = statement.executeQuery()) {
+                return row.next() ? row.getString("name") : uuid.toString();
+            }
+        }
+    }
+
+    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 ?
+            """;
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, uuid.toString());
+            statement.setInt(2, limit);
+            List<String> networks = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) networks.add(row.getString("network"));
+            }
+            return networks;
+        }
+    }
+
+    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 (?, ?, ?, ?, ?)";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, network);
+            statement.setObject(2, toDb(from));
+            statement.setObject(3, toDb(until));
+            statement.setString(4, admin.toString());
+            statement.setString(5, note);
+            statement.executeUpdate();
+        }
+    }
+
+    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"));
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setObject(1, toDb(now));
+            List<Exemption> exemptions = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) exemptions.add(new Exemption(
+                    row.getLong("id"),
+                    row.getString("network"),
+                    fromDb(row, "valid_from"),
+                    fromDb(row, "valid_until"),
+                    row.getString("created_by_name"),
+                    row.getString("note")
+                ));
+            }
+            return exemptions;
+        }
+    }
+
+    void endExemption(Connection connection, long id, Instant now) throws SQLException {
+        try(PreparedStatement statement = connection.prepareStatement("UPDATE ban_evasion_ip_exemptions SET valid_until = ? WHERE id = ? AND valid_until > ?")) {
+            statement.setObject(1, toDb(now));
+            statement.setLong(2, id);
+            statement.setObject(3, toDb(now));
+            statement.executeUpdate();
+        }
+    }
+
+    /**
+     * 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() ? this.createHousehold(connection, admin, note, at) : existing.getFirst();
+            for(long other : existing.subList(Math.min(1, existing.size()), existing.size())) {
+                try(PreparedStatement move = connection.prepareStatement("UPDATE ban_evasion_household_members SET household_id = ? WHERE household_id = ?")) {
+                    move.setLong(1, target);
+                    move.setLong(2, other);
+                    move.executeUpdate();
+                }
+                try(PreparedStatement delete = connection.prepareStatement("DELETE FROM ban_evasion_households WHERE id = ?")) {
+                    delete.setLong(1, other);
+                    delete.executeUpdate();
+                }
+            }
+            try(PreparedStatement insert = connection.prepareStatement("INSERT IGNORE INTO ban_evasion_household_members (uuid, household_id) VALUES (?, ?)")) {
+                for(UUID uuid : uuids) {
+                    insert.setString(1, uuid.toString());
+                    insert.setLong(2, target);
+                    insert.addBatch();
+                }
+                insert.executeBatch();
+            }
+            connection.commit();
+        } catch(SQLException e) {
+            connection.rollback();
+            throw e;
+        } finally {
+            connection.setAutoCommit(autoCommit);
+        }
+    }
+
+    List<Household> listHouseholds(Connection connection) throws SQLException {
+        String sql = """
+            SELECT h.id, h.note, m.uuid, %s AS name
+            FROM ban_evasion_households h
+            JOIN ban_evasion_household_members m ON m.household_id = h.id
+            ORDER BY h.id, name
+            """.formatted(NAME_OF.formatted("m.uuid"));
+        Map<Long, Household> households = new LinkedHashMap<>();
+        try(PreparedStatement statement = connection.prepareStatement(sql); ResultSet row = statement.executeQuery()) {
+            while(row.next()) {
+                long id = row.getLong("id");
+                String householdNote = row.getString("note");
+                UUID uuid = UUID.fromString(row.getString("uuid"));
+                households.computeIfAbsent(id, key -> new Household(key, householdNote, new ArrayList<>()))
+                    .members().add(new Member(uuid, nameOr(row.getString("name"), uuid)));
+            }
+        }
+        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;
+        try(PreparedStatement delete = connection.prepareStatement("DELETE FROM ban_evasion_household_members WHERE uuid = ?")) {
+            delete.setString(1, uuid.toString());
+            delete.executeUpdate();
+        }
+        String sql = "DELETE FROM ban_evasion_households WHERE id = ? AND (SELECT COUNT(*) FROM ban_evasion_household_members WHERE household_id = ?) < 2";
+        try(PreparedStatement dissolve = connection.prepareStatement(sql)) {
+            dissolve.setLong(1, household);
+            dissolve.setLong(2, household);
+            dissolve.executeUpdate();
+        }
+    }
+
+    int deleteExpired(Connection connection, int retentionMonths) throws SQLException {
+        int deleted = 0;
+        for(String sql : List.of(
+            "DELETE FROM ban_evasion_cases WHERE last_seen_at < UTC_TIMESTAMP() - INTERVAL ? MONTH",
+            "DELETE FROM ban_evasion_ip_exemptions WHERE valid_until < UTC_TIMESTAMP() - INTERVAL ? MONTH"
+        )) {
+            try(PreparedStatement statement = connection.prepareStatement(sql)) {
+                statement.setInt(1, retentionMonths);
+                deleted += statement.executeUpdate();
+            }
+        }
+        return deleted;
+    }
+
+    private long createHousehold(Connection connection, UUID admin, @Nullable String note, Instant at) throws SQLException {
+        String sql = "INSERT INTO ban_evasion_households (created_at, created_by, note) VALUES (?, ?, ?)";
+        try(PreparedStatement statement = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
+            statement.setObject(1, toDb(at));
+            statement.setString(2, admin.toString());
+            statement.setString(3, note);
+            statement.executeUpdate();
+            try(ResultSet keys = statement.getGeneratedKeys()) {
+                keys.next();
+                return keys.getLong(1);
+            }
+        }
+    }
+
+    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";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setLong(1, caseId);
+            List<CaseReason> reasons = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) reasons.add(new CaseReason(
+                    Reason.valueOf(row.getString("reason")),
+                    Severity.valueOf(row.getString("severity")),
+                    fromDb(row, "first_seen_at")
+                ));
+            }
+            return reasons;
+        }
+    }
+
+    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
+            """;
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, first.toString());
+            statement.setString(2, second.toString());
+            List<String> networks = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) networks.add(row.getString("network"));
+            }
+            return networks;
+        }
+    }
+
+    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 ?";
+        try(PreparedStatement statement = connection.prepareStatement(sql)) {
+            statement.setString(1, first.toString());
+            statement.setString(2, second.toString());
+            statement.setInt(3, limit);
+            List<TimelineEntry> entries = new ArrayList<>();
+            try(ResultSet row = statement.executeQuery()) {
+                while(row.next()) entries.add(new TimelineEntry(
+                    fromDb(row, "at"), row.getString("name"), row.getString("network"), row.getString("stage"), row.getString("result")
+                ));
+            }
+            return entries;
+        }
+    }
+
+    private static CaseSummary summaryOf(ResultSet row) throws SQLException {
+        UUID first = UUID.fromString(row.getString("uuid_a"));
+        UUID second = UUID.fromString(row.getString("uuid_b"));
+        String outcome = row.getString("outcome");
+        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")),
+            outcome == null ? null : Outcome.valueOf(outcome),
+            Severity.valueOf(row.getString("severity")),
+            fromDb(row, "last_seen_at"),
+            row.getInt("hits")
+        );
+    }
+
+    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 row.getObject(column, LocalDateTime.class).toInstant(ZoneOffset.UTC);
+    }
+
+    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 +1,48 @@
+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.
+ * 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 Clock clock;
+
+    BanStatusCache(Function<UUID, BanState> lookup, Duration ttl, Clock clock) {
+        this.lookup = lookup;
+        this.ttl = ttl;
+        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();
+
+        BanState state = this.lookup.apply(uuid);
+        if(state == BanState.UNKNOWN) this.entries.remove(uuid);
+        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 +1,40 @@
+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.
+ */
+final class CaseDecision {
+    record ExistingCase(long id, CaseStatus status, 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);
+        return new Result(newHigh, newReasons, newHigh);
+    }
+}

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

@@ -0,0 +1,102 @@
+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;
+import java.util.stream.Collectors;
+
+/**
+ * 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 && householdState(input, household) != BanState.BANNED) 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 BanState householdState(Input input, long household) {
+        Set<BanState> states = input.householdMembers().getOrDefault(household, Set.of()).stream()
+            .map(member -> banState(input, member))
+            .collect(Collectors.toSet());
+        if(states.contains(BanState.BANNED)) return BanState.BANNED;
+        if(states.contains(BanState.UNKNOWN)) return BanState.UNKNOWN;
+        return BanState.NOT_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;