2026-07-24 08:41:09 +00:00
27 changed files with 1274 additions and 207 deletions
--- a/.env.example
+++ b/.env.example
@@ -39,3 +39,24 @@ LEGAL_OPERATOR_NAME=HexaHost Inh. Samuel Müller
 LEGAL_OPERATOR_ADDRESS=Richard-Miller-Straße 1, 94051 Hauzenberg, Deutschland
 LEGAL_OPERATOR_EMAIL=info@hexahost.de
 LEGAL_OPERATOR_PHONE=+49 15566 175855
+
+# ---------------------------------------------------------------------------
+# Verification captcha providers (WebUI). Leave empty to disable a provider.
+# MATH always works without keys. Per-guild provider is chosen in the dashboard.
+# ---------------------------------------------------------------------------
+# Google reCAPTCHA v2 (checkbox) – https://www.google.com/recaptcha/admin
+RECAPTCHA_SITE_KEY=
+RECAPTCHA_SECRET_KEY=
+# Google reCAPTCHA v3 (score-based). Falls back to RECAPTCHA_* if unset.
+RECAPTCHA_V3_SITE_KEY=
+RECAPTCHA_V3_SECRET_KEY=
+RECAPTCHA_V3_MIN_SCORE=0.5
+# hCaptcha – https://dashboard.hcaptcha.com
+HCAPTCHA_SITE_KEY=
+HCAPTCHA_SECRET_KEY=
+# Cloudflare Turnstile – https://dash.cloudflare.com → Turnstile
+TURNSTILE_SITE_KEY=
+TURNSTILE_SECRET_KEY=
+# Salt for hashing client IPs used in alt-account detection (min 16 chars).
+# Generate e.g. with: openssl rand -hex 16
+CAPTCHA_IP_HASH_SALT=
--- a/apps/bot/prisma/migrations/20260723120000_verification_captcha_alt/migration.sql
+++ b/apps/bot/prisma/migrations/20260723120000_verification_captcha_alt/migration.sql
@@ -0,0 +1,37 @@
+-- AlterTable
+ALTER TABLE "VerificationConfig" ADD COLUMN IF NOT EXISTS "captchaProvider" TEXT NOT NULL DEFAULT 'MATH';
+ALTER TABLE "VerificationConfig" ADD COLUMN IF NOT EXISTS "altDetectionEnabled" BOOLEAN NOT NULL DEFAULT false;
+ALTER TABLE "VerificationConfig" ADD COLUMN IF NOT EXISTS "altBlockOnMatch" BOOLEAN NOT NULL DEFAULT true;
+ALTER TABLE "VerificationConfig" ADD COLUMN IF NOT EXISTS "altIpWindowDays" INTEGER NOT NULL DEFAULT 30;
+ALTER TABLE "VerificationConfig" ADD COLUMN IF NOT EXISTS "altInviteWindowHours" INTEGER NOT NULL DEFAULT 48;
+ALTER TABLE "VerificationConfig" ADD COLUMN IF NOT EXISTS "altMaxAccountsPerInvite" INTEGER NOT NULL DEFAULT 3;
+
+-- CreateTable
+CREATE TABLE IF NOT EXISTS "VerificationRecord" (
+    "id" TEXT NOT NULL,
+    "guildId" TEXT NOT NULL,
+    "userId" TEXT NOT NULL,
+    "inviteCode" TEXT,
+    "inviterId" TEXT,
+    "ipHash" TEXT,
+    "userAgentHash" TEXT,
+    "captchaProvider" TEXT,
+    "flaggedAsAlt" BOOLEAN NOT NULL DEFAULT false,
+    "matchedUserId" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "VerificationRecord_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX IF NOT EXISTS "VerificationRecord_guildId_userId_key" ON "VerificationRecord"("guildId", "userId");
+CREATE INDEX IF NOT EXISTS "VerificationRecord_guildId_ipHash_createdAt_idx" ON "VerificationRecord"("guildId", "ipHash", "createdAt");
+CREATE INDEX IF NOT EXISTS "VerificationRecord_guildId_inviteCode_createdAt_idx" ON "VerificationRecord"("guildId", "inviteCode", "createdAt");
+
+-- AddForeignKey
+DO $$ BEGIN
+  ALTER TABLE "VerificationRecord" ADD CONSTRAINT "VerificationRecord_guildId_fkey"
+    FOREIGN KEY ("guildId") REFERENCES "Guild"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+EXCEPTION
+  WHEN duplicate_object THEN NULL;
+END $$;
--- a/apps/bot/prisma/schema.prisma
+++ b/apps/bot/prisma/schema.prisma
@@ -20,6 +20,7 @@ model Guild {
  logChannels LogChannel[]
  welcomeConfig WelcomeConfig?
  verificationConfig VerificationConfig?
+  verificationRecords VerificationRecord[]
  levelingConfig LevelingConfig?
  memberLevels MemberLevel[]
  levelRewards LevelReward[]
@@ -263,20 +264,47 @@ model WelcomeConfig {
 }

 model VerificationConfig {
-  id               String   @id @default(cuid())
-  guildId          String   @unique
-  enabled          Boolean  @default(false)
-  channelId        String?
-  verifiedRoleId   String?
-  unverifiedRoleId String?
-  mode             String   @default("BUTTON")
-  minAccountAgeDays Int     @default(0)
-  failAction       String   @default("KICK")
-  panelChannelId   String?
-  panelMessageId   String?
-  createdAt        DateTime @default(now())
-  updatedAt        DateTime @updatedAt
-  guild            Guild    @relation(fields: [guildId], references: [id], onDelete: Cascade)
+  id                    String   @id @default(cuid())
+  guildId               String   @unique
+  enabled               Boolean  @default(false)
+  channelId             String?
+  verifiedRoleId        String?
+  unverifiedRoleId      String?
+  mode                  String   @default("BUTTON")
+  /// MATH | RECAPTCHA_V2 | RECAPTCHA_V3 | HCAPTCHA | TURNSTILE
+  captchaProvider       String   @default("MATH")
+  minAccountAgeDays     Int      @default(0)
+  failAction            String   @default("KICK")
+  altDetectionEnabled   Boolean  @default(false)
+  altBlockOnMatch       Boolean  @default(true)
+  altIpWindowDays       Int      @default(30)
+  altInviteWindowHours  Int      @default(48)
+  altMaxAccountsPerInvite Int    @default(3)
+  panelChannelId        String?
+  panelMessageId        String?
+  createdAt             DateTime @default(now())
+  updatedAt             DateTime @updatedAt
+  guild                 Guild    @relation(fields: [guildId], references: [id], onDelete: Cascade)
+}
+
+/// One row per successful (or blocked-as-alt) verification attempt fingerprint.
+model VerificationRecord {
+  id              String   @id @default(cuid())
+  guildId         String
+  userId          String
+  inviteCode      String?
+  inviterId       String?
+  ipHash          String?
+  userAgentHash   String?
+  captchaProvider String?
+  flaggedAsAlt    Boolean  @default(false)
+  matchedUserId   String?
+  createdAt       DateTime @default(now())
+  guild           Guild    @relation(fields: [guildId], references: [id], onDelete: Cascade)
+
+  @@unique([guildId, userId])
+  @@index([guildId, ipHash, createdAt])
+  @@index([guildId, inviteCode, createdAt])
 }

 model LevelingConfig {
--- a/apps/bot/src/env.ts
+++ b/apps/bot/src/env.ts
@@ -39,7 +39,9 @@ const EnvSchema = z.object({
      )
  ),
  WEBUI_URL: z.preprocess(emptyToUndefined, z.string().url().optional()),
-  SUPPORT_SERVER_URL: z.preprocess(emptyToUndefined, z.string().url().optional())
+  SUPPORT_SERVER_URL: z.preprocess(emptyToUndefined, z.string().url().optional()),
+  /// Salt for hashing client IPs in verification alt-detection (shared with WebUI).
+  CAPTCHA_IP_HASH_SALT: z.preprocess(emptyToUndefined, z.string().min(16).optional())
 });

 export const env = EnvSchema.parse(process.env);
--- a/apps/bot/src/health.ts
+++ b/apps/bot/src/health.ts
@@ -71,9 +71,17 @@ async function handleCaptchaGet(url: URL, res: ServerResponse): Promise<void> {
    res.end('Captcha expired');
    return;
  }
+  // External providers (reCAPTCHA / hCaptcha / Turnstile) are served by the WebUI.
+  if (challenge.provider !== 'MATH' && env.WEBUI_URL) {
+    const target = `${env.WEBUI_URL.replace(/\/$/, '')}/verify/captcha?token=${encodeURIComponent(token)}`;
+    res.statusCode = 302;
+    res.setHeader('Location', target);
+    res.end();
+    return;
+  }
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/html; charset=utf-8');
-  res.end(renderCaptchaPage(token, challenge.question));
+  res.end(renderCaptchaPage(token, challenge.question ?? '?'));
 }

 async function handleCaptchaPost(req: IncomingMessage, res: ServerResponse): Promise<void> {
@@ -92,16 +100,32 @@ async function handleCaptchaPost(req: IncomingMessage, res: ServerResponse): Pro
    res.end('Captcha expired');
    return;
  }
-  if (hashCaptchaAnswer(answer) !== challenge.answerHash) {
+  if (challenge.provider !== 'MATH') {
+    if (env.WEBUI_URL) {
+      const target = `${env.WEBUI_URL.replace(/\/$/, '')}/verify/captcha?token=${encodeURIComponent(token)}`;
+      res.statusCode = 302;
+      res.setHeader('Location', target);
+      res.end();
+      return;
+    }
+    res.statusCode = 400;
+    res.end('Use the WebUI captcha URL for this provider');
+    return;
+  }
+  if (!challenge.answerHash || hashCaptchaAnswer(answer) !== challenge.answerHash) {
    res.statusCode = 200;
    res.setHeader('Content-Type', 'text/html; charset=utf-8');
-    res.end(renderCaptchaPage(token, challenge.question, 'Wrong answer. Try again.'));
+    res.end(renderCaptchaPage(token, challenge.question ?? '?', 'Wrong answer. Try again.'));
    return;
  }
  await deleteCaptchaChallenge(redis, token);
  await verificationQueue.add(
    'verificationComplete',
-    { guildId: challenge.guildId, userId: challenge.userId },
+    {
+      guildId: challenge.guildId,
+      userId: challenge.userId,
+      captchaProvider: challenge.provider
+    },
    { removeOnComplete: 1000, removeOnFail: 500 }
  );
  res.statusCode = 200;
--- a/apps/bot/src/jobs.ts
+++ b/apps/bot/src/jobs.ts
@@ -65,6 +65,9 @@ type TempBanJob = {
 type VerificationCompleteJob = {
  guildId: string;
  userId: string;
+  ipHash?: string | null;
+  userAgentHash?: string | null;
+  captchaProvider?: string | null;
 };

 type ReminderSendJob = {
@@ -228,7 +231,11 @@ export function startWorkers(context: BotContext): Worker[] {
      if (job.name !== 'verificationComplete') {
        return;
      }
-      await completeVerification(context, job.data.guildId, job.data.userId);
+      await completeVerification(context, job.data.guildId, job.data.userId, {
+        ipHash: job.data.ipHash,
+        userAgentHash: job.data.userAgentHash,
+        captchaProvider: job.data.captchaProvider
+      });
    },
    { connection: redis }
  );
--- a/apps/bot/src/modules/verification/alt-detection.test.ts
+++ b/apps/bot/src/modules/verification/alt-detection.test.ts
@@ -0,0 +1,83 @@
+import { describe, expect, it } from 'vitest';
+import { detectAltAccount } from './alt-detection.js';
+
+describe('detectAltAccount', () => {
+  const basePrior = {
+    userId: 'user-a',
+    inviteCode: 'abc123',
+    ipHash: 'ip-hash-1',
+    createdAt: new Date(),
+    flaggedAsAlt: false
+  };
+
+  it('matches identical IP hash within window', () => {
+    const match = detectAltAccount({
+      userId: 'user-b',
+      accountAgeDays: 30,
+      inviteCode: null,
+      ipHash: 'ip-hash-1',
+      priorRecords: [basePrior],
+      altIpWindowDays: 30,
+      altInviteWindowHours: 48,
+      altMaxAccountsPerInvite: 3
+    });
+    expect(match).toEqual({ reason: 'ip', matchedUserId: 'user-a' });
+  });
+
+  it('does not match when IP window expired', () => {
+    const match = detectAltAccount({
+      userId: 'user-b',
+      accountAgeDays: 30,
+      inviteCode: null,
+      ipHash: 'ip-hash-1',
+      priorRecords: [
+        {
+          ...basePrior,
+          createdAt: new Date(Date.now() - 40 * 24 * 60 * 60 * 1000)
+        }
+      ],
+      altIpWindowDays: 30,
+      altInviteWindowHours: 48,
+      altMaxAccountsPerInvite: 3
+    });
+    expect(match).toBeNull();
+  });
+
+  it('flags invite clusters for young accounts', () => {
+    const now = Date.now();
+    const match = detectAltAccount({
+      userId: 'user-new',
+      accountAgeDays: 2,
+      inviteCode: 'raid',
+      ipHash: null,
+      priorRecords: [
+        { ...basePrior, userId: 'u1', inviteCode: 'raid', createdAt: new Date(now - 60_000) },
+        { ...basePrior, userId: 'u2', inviteCode: 'raid', createdAt: new Date(now - 120_000) },
+        { ...basePrior, userId: 'u3', inviteCode: 'raid', createdAt: new Date(now - 180_000) }
+      ],
+      altIpWindowDays: 30,
+      altInviteWindowHours: 48,
+      altMaxAccountsPerInvite: 3
+    });
+    expect(match?.reason).toBe('invite_cluster');
+  });
+
+  it('ignores invite clusters for older accounts', () => {
+    const now = Date.now();
+    const match = detectAltAccount({
+      userId: 'user-old',
+      accountAgeDays: 90,
+      inviteCode: 'raid',
+      ipHash: null,
+      priorRecords: [
+        { ...basePrior, userId: 'u1', inviteCode: 'raid', createdAt: new Date(now - 60_000) },
+        { ...basePrior, userId: 'u2', inviteCode: 'raid', createdAt: new Date(now - 120_000) },
+        { ...basePrior, userId: 'u3', inviteCode: 'raid', createdAt: new Date(now - 180_000) }
+      ],
+      altIpWindowDays: 30,
+      altInviteWindowHours: 48,
+      altMaxAccountsPerInvite: 3
+    });
+    expect(match).toBeNull();
+  });
+});
--- a/apps/bot/src/modules/verification/alt-detection.ts
+++ b/apps/bot/src/modules/verification/alt-detection.ts
@@ -0,0 +1,62 @@
+export type AltSignalMatch = {
+  reason: 'ip' | 'invite_cluster';
+  matchedUserId: string | null;
+};
+
+export type AltDetectionInput = {
+  userId: string;
+  accountAgeDays: number;
+  inviteCode: string | null;
+  ipHash: string | null;
+  /** Prior verification records in the same guild (excluding current user). */
+  priorRecords: Array<{
+    userId: string;
+    inviteCode: string | null;
+    ipHash: string | null;
+    createdAt: Date;
+    flaggedAsAlt: boolean;
+  }>;
+  altIpWindowDays: number;
+  altInviteWindowHours: number;
+  altMaxAccountsPerInvite: number;
+  /** Only flag invite clusters when the current account is this young or younger. */
+  youngAccountMaxDays?: number;
+};
+
+/**
+ * Detects likely alt accounts from Discord + captcha signals.
+ * Does not use browser fingerprinting beyond salted IP / UA hashes from the captcha page.
+ */
+export function detectAltAccount(input: AltDetectionInput): AltSignalMatch | null {
+  const youngMax = input.youngAccountMaxDays ?? 7;
+  const now = Date.now();
+
+  if (input.ipHash) {
+    const ipWindowMs = input.altIpWindowDays * 24 * 60 * 60 * 1000;
+    const ipMatch = input.priorRecords.find(
+      (record) =>
+        record.ipHash === input.ipHash &&
+        now - record.createdAt.getTime() <= ipWindowMs
+    );
+    if (ipMatch) {
+      return { reason: 'ip', matchedUserId: ipMatch.userId };
+    }
+  }
+
+  if (input.inviteCode && input.accountAgeDays <= youngMax) {
+    const inviteWindowMs = input.altInviteWindowHours * 60 * 60 * 1000;
+    const recentSameInvite = input.priorRecords.filter(
+      (record) =>
+        record.inviteCode === input.inviteCode &&
+        now - record.createdAt.getTime() <= inviteWindowMs
+    );
+    if (recentSameInvite.length >= input.altMaxAccountsPerInvite) {
+      return {
+        reason: 'invite_cluster',
+        matchedUserId: recentSameInvite[0]?.userId ?? null
+      };
+    }
+  }
+
+  return null;
+}
--- a/apps/bot/src/modules/verification/command-definitions.ts
+++ b/apps/bot/src/modules/verification/command-definitions.ts
@@ -26,6 +26,18 @@ export const verifyCommandData = applyCommandDescription(
              { name: 'Captcha', value: 'CAPTCHA' }
            )
        )
+        .addStringOption((o) =>
+          applyOptionDescription(
+            o.setName('captcha_provider'),
+            'verify.setup.options.captcha_provider'
+          ).addChoices(
+            { name: 'Math', value: 'MATH' },
+            { name: 'reCAPTCHA v2', value: 'RECAPTCHA_V2' },
+            { name: 'reCAPTCHA v3', value: 'RECAPTCHA_V3' },
+            { name: 'hCaptcha', value: 'HCAPTCHA' },
+            { name: 'Turnstile', value: 'TURNSTILE' }
+          )
+        )
        .addIntegerOption((o) =>
          applyOptionDescription(o.setName('min_account_age_days'), 'verify.setup.options.min_account_age_days')
            .setMinValue(0)
@@ -39,6 +51,9 @@ export const verifyCommandData = applyCommandDescription(
              { name: 'None', value: 'NONE' }
            )
        )
+        .addBooleanOption((o) =>
+          applyOptionDescription(o.setName('alt_detection'), 'verify.setup.options.alt_detection')
+        )
    )
    .addSubcommand((s) =>
      applyCommandDescription(s.setName('panel'), 'verify.panel.description')
--- a/apps/bot/src/modules/verification/commands.ts
+++ b/apps/bot/src/modules/verification/commands.ts
@@ -50,11 +50,20 @@ const verifyCommand: SlashCommand = {
      const verifiedRole = interaction.options.getRole('verified_role', true);
      const unverifiedRole = interaction.options.getRole('unverified_role');
      const mode = (interaction.options.getString('mode') ?? 'BUTTON') as 'BUTTON' | 'CAPTCHA';
+      const captchaProvider = (interaction.options.getString('captcha_provider') ??
+        'MATH') as
+        | 'MATH'
+        | 'RECAPTCHA_V2'
+        | 'RECAPTCHA_V3'
+        | 'HCAPTCHA'
+        | 'TURNSTILE';
      const minAccountAgeDays = interaction.options.getInteger('min_account_age_days') ?? 0;
      const failAction = (interaction.options.getString('fail_action') ?? 'KICK') as
        | 'KICK'
        | 'BAN'
        | 'NONE';
+      const altDetectionEnabled =
+        interaction.options.getBoolean('alt_detection') ?? false;

      await updateVerificationConfig(context.prisma, guildId, {
        enabled: true,
@@ -62,8 +71,10 @@ const verifyCommand: SlashCommand = {
        verifiedRoleId: verifiedRole.id,
        unverifiedRoleId: unverifiedRole?.id ?? null,
        mode,
+        captchaProvider,
        minAccountAgeDays,
-        failAction
+        failAction,
+        altDetectionEnabled
      });

      await interaction.reply({ content: t(locale, 'verification.setupDone'), ...ephemeral() });
--- a/apps/bot/src/modules/verification/handlers.ts
+++ b/apps/bot/src/modules/verification/handlers.ts
@@ -7,7 +7,7 @@ import {
  type ButtonInteraction,
  type GuildMember
 } from 'discord.js';
-import { t, tf } from '@nexumi/shared';
+import { CaptchaProviderSchema, t, tf, type CaptchaProvider } from '@nexumi/shared';
 import type { BotContext } from '../../types.js';
 import { getGuildLocale } from '../../i18n.js';
 import {
@@ -18,10 +18,17 @@ import {
  verificationButtonId,
  verificationCaptchaButtonId
 } from './service.js';
+import { detectAltAccount } from './alt-detection.js';
 import { env } from '../../env.js';
 import { logger } from '../../logger.js';
 import { ephemeral } from '../../interaction-reply.js';

+export type CompleteVerificationOptions = {
+  ipHash?: string | null;
+  userAgentHash?: string | null;
+  captchaProvider?: string | null;
+};
+
 async function applyFailAction(
  member: GuildMember,
  failAction: string,
@@ -40,7 +47,8 @@ async function applyFailAction(
 export async function completeVerification(
  context: BotContext,
  guildId: string,
-  userId: string
+  userId: string,
+  options: CompleteVerificationOptions = {}
 ): Promise<{ ok: boolean; reason?: string }> {
  const config = await getVerificationConfig(context.prisma, guildId);
  if (!config.enabled || !config.verifiedRoleId) {
@@ -63,6 +71,88 @@ export async function completeVerification(
    return { ok: false, reason: 'account_too_young' };
  }

+  const inviteJoin = await context.prisma.inviteJoin.findUnique({
+    where: { guildId_userId: { guildId, userId } }
+  });
+
+  let flaggedAsAlt = false;
+  let matchedUserId: string | null = null;
+
+  if (config.altDetectionEnabled) {
+    const lookbackMs = Math.max(
+      config.altIpWindowDays * 24 * 60 * 60 * 1000,
+      config.altInviteWindowHours * 60 * 60 * 1000
+    );
+    const since = new Date(Date.now() - lookbackMs);
+    const priorRecords = await context.prisma.verificationRecord.findMany({
+      where: {
+        guildId,
+        userId: { not: userId },
+        createdAt: { gte: since }
+      },
+      select: {
+        userId: true,
+        inviteCode: true,
+        ipHash: true,
+        createdAt: true,
+        flaggedAsAlt: true
+      }
+    });
+
+    const match = detectAltAccount({
+      userId,
+      accountAgeDays: ageDays,
+      inviteCode: inviteJoin?.code ?? null,
+      ipHash: options.ipHash ?? null,
+      priorRecords,
+      altIpWindowDays: config.altIpWindowDays,
+      altInviteWindowHours: config.altInviteWindowHours,
+      altMaxAccountsPerInvite: config.altMaxAccountsPerInvite
+    });
+
+    if (match) {
+      flaggedAsAlt = true;
+      matchedUserId = match.matchedUserId;
+      logger.info(
+        { guildId, userId, reason: match.reason, matchedUserId },
+        'Verification alt-account signal'
+      );
+
+      await context.prisma.verificationRecord.upsert({
+        where: { guildId_userId: { guildId, userId } },
+        create: {
+          guildId,
+          userId,
+          inviteCode: inviteJoin?.code ?? null,
+          inviterId: inviteJoin?.inviterId ?? null,
+          ipHash: options.ipHash ?? null,
+          userAgentHash: options.userAgentHash ?? null,
+          captchaProvider: options.captchaProvider ?? null,
+          flaggedAsAlt: true,
+          matchedUserId
+        },
+        update: {
+          inviteCode: inviteJoin?.code ?? null,
+          inviterId: inviteJoin?.inviterId ?? null,
+          ipHash: options.ipHash ?? null,
+          userAgentHash: options.userAgentHash ?? null,
+          captchaProvider: options.captchaProvider ?? null,
+          flaggedAsAlt: true,
+          matchedUserId
+        }
+      });
+
+      if (config.altBlockOnMatch) {
+        await applyFailAction(
+          member,
+          config.failAction,
+          `Verification failed: possible alt account (${match.reason})`
+        );
+        return { ok: false, reason: 'alt_detected' };
+      }
+    }
+  }
+
  const me = guild.members.me;
  if (!me?.permissions.has(PermissionFlagsBits.ManageRoles)) {
    return { ok: false, reason: 'missing_permissions' };
@@ -83,6 +173,30 @@ export async function completeVerification(
    await member.roles.add(config.verifiedRoleId);
  }

+  await context.prisma.verificationRecord.upsert({
+    where: { guildId_userId: { guildId, userId } },
+    create: {
+      guildId,
+      userId,
+      inviteCode: inviteJoin?.code ?? null,
+      inviterId: inviteJoin?.inviterId ?? null,
+      ipHash: options.ipHash ?? null,
+      userAgentHash: options.userAgentHash ?? null,
+      captchaProvider: options.captchaProvider ?? null,
+      flaggedAsAlt,
+      matchedUserId
+    },
+    update: {
+      inviteCode: inviteJoin?.code ?? null,
+      inviterId: inviteJoin?.inviterId ?? null,
+      ipHash: options.ipHash ?? null,
+      userAgentHash: options.userAgentHash ?? null,
+      captchaProvider: options.captchaProvider ?? null,
+      flaggedAsAlt,
+      matchedUserId
+    }
+  });
+
  return { ok: true };
 }

@@ -132,10 +246,13 @@ export async function handleVerificationButton(
  }

  if (parsed.mode === 'captcha') {
+    const providerParse = CaptchaProviderSchema.safeParse(config.captchaProvider);
+    const provider: CaptchaProvider = providerParse.success ? providerParse.data : 'MATH';
    const challenge = await createCaptchaChallenge(
      context.redis,
      parsed.guildId,
-      interaction.user.id
+      interaction.user.id,
+      provider
    );
    const base = (env.WEBUI_URL ?? env.PUBLIC_BASE_URL).replace(/\/$/, '');
    const url = `${base}/verify/captcha?token=${challenge.token}`;
--- a/apps/bot/src/modules/verification/service.ts
+++ b/apps/bot/src/modules/verification/service.ts
@@ -1,11 +1,27 @@
-import { randomBytes, randomInt, createHash } from 'node:crypto';
+import { createHash, randomBytes, randomInt } from 'node:crypto';
+import type { CaptchaProvider, VerificationFailAction, VerificationMode } from '@nexumi/shared';
 import type { PrismaClient } from '@prisma/client';
-import type { VerificationFailAction, VerificationMode } from '@nexumi/shared';
-import { ensureGuild } from '../../guild.js';
 import type { Redis } from 'ioredis';
+import { ensureGuild } from '../../guild.js';

 const CAPTCHA_PREFIX = 'verify:captcha:';

+export type VerificationConfigUpdate = {
+  enabled: boolean;
+  channelId: string;
+  verifiedRoleId: string;
+  unverifiedRoleId?: string | null;
+  mode: VerificationMode;
+  captchaProvider?: CaptchaProvider;
+  minAccountAgeDays: number;
+  failAction: VerificationFailAction;
+  altDetectionEnabled?: boolean;
+  altBlockOnMatch?: boolean;
+  altIpWindowDays?: number;
+  altInviteWindowHours?: number;
+  altMaxAccountsPerInvite?: number;
+};
+
 export async function getVerificationConfig(prisma: PrismaClient, guildId: string) {
  await ensureGuild(prisma, guildId);
  let config = await prisma.verificationConfig.findUnique({ where: { guildId } });
@@ -18,15 +34,7 @@ export async function getVerificationConfig(prisma: PrismaClient, guildId: strin
 export async function updateVerificationConfig(
  prisma: PrismaClient,
  guildId: string,
-  data: {
-    enabled: boolean;
-    channelId: string;
-    verifiedRoleId: string;
-    unverifiedRoleId?: string | null;
-    mode: VerificationMode;
-    minAccountAgeDays: number;
-    failAction: VerificationFailAction;
-  }
+  data: VerificationConfigUpdate
 ) {
  await ensureGuild(prisma, guildId);
  return prisma.verificationConfig.upsert({
@@ -65,27 +73,32 @@ export type CaptchaChallenge = {
  token: string;
  guildId: string;
  userId: string;
-  question: string;
-  answerHash: string;
+  provider: CaptchaProvider;
+  question?: string;
+  answerHash?: string;
 };

 export async function createCaptchaChallenge(
  redis: Redis,
  guildId: string,
-  userId: string
+  userId: string,
+  provider: CaptchaProvider = 'MATH'
 ): Promise<CaptchaChallenge> {
-  const a = randomInt(2, 12);
-  const b = randomInt(2, 12);
-  const answer = String(a + b);
  const token = randomBytes(24).toString('hex');
-  const answerHash = createHash('sha256').update(answer).digest('hex');
  const challenge: CaptchaChallenge = {
    token,
    guildId,
    userId,
-    question: `${a} + ${b}`,
-    answerHash
+    provider
  };
+
+  if (provider === 'MATH') {
+    const a = randomInt(2, 12);
+    const b = randomInt(2, 12);
+    challenge.question = `${a} + ${b}`;
+    challenge.answerHash = createHash('sha256').update(String(a + b)).digest('hex');
+  }
+
  await redis.set(`${CAPTCHA_PREFIX}${token}`, JSON.stringify(challenge), 'EX', 600);
  return challenge;
 }
@@ -98,7 +111,11 @@ export async function getCaptchaChallenge(
  if (!raw) {
    return null;
  }
-  return JSON.parse(raw) as CaptchaChallenge;
+  const parsed = JSON.parse(raw) as CaptchaChallenge;
+  if (!parsed.provider) {
+    parsed.provider = 'MATH';
+  }
+  return parsed;
 }

 export async function deleteCaptchaChallenge(redis: Redis, token: string): Promise<void> {
@@ -113,3 +130,7 @@ export function accountAgeDays(userCreatedAt: Date): number {
  const ms = Date.now() - userCreatedAt.getTime();
  return Math.floor(ms / (1000 * 60 * 60 * 24));
 }
+
+export function hashClientSignal(salt: string, value: string): string {
+  return createHash('sha256').update(`${salt}:${value}`).digest('hex');
+}
--- a/apps/webui/src/app/api/guilds/[guildId]/verification/route.ts
+++ b/apps/webui/src/app/api/guilds/[guildId]/verification/route.ts
@@ -13,8 +13,8 @@ export async function GET(_request: NextRequest, { params }: RouteParams) {
  const { guildId } = await params;
  try {
    await requireGuildAccess(guildId);
-    const config = await getVerificationDashboard(guildId);
-    return NextResponse.json(config);
+    const payload = await getVerificationDashboard(guildId);
+    return NextResponse.json(payload);
  } catch (error) {
    return toApiErrorResponse(error);
  }
@@ -28,15 +28,19 @@ export async function PATCH(request: NextRequest, { params }: RouteParams) {
    const patch = VerificationConfigDashboardPatchSchema.parse(body);

    const before = await getVerificationDashboard(guildId);
-    const after = await updateVerificationDashboard(guildId, patch);
+    const afterConfig = await updateVerificationDashboard(guildId, patch);
+    const after = {
+      config: afterConfig,
+      availableCaptchaProviders: before.availableCaptchaProviders
+    };

    await writeDashboardAudit(prisma, {
      guildId,
      actorUserId: session.user.id,
      action: 'verification.update',
      path: `/dashboard/${guildId}/verification`,
-      before,
-      after
+      before: before.config,
+      after: afterConfig
    });

    return NextResponse.json(after);
--- a/apps/webui/src/app/dashboard/[guildId]/verification/page.tsx
+++ b/apps/webui/src/app/dashboard/[guildId]/verification/page.tsx
@@ -8,7 +8,7 @@ interface VerificationPageProps {

 export default async function VerificationPage({ params }: VerificationPageProps) {
  const { guildId } = await params;
-  const [locale, config] = await Promise.all([getLocale(), getVerificationDashboard(guildId)]);
+  const [locale, payload] = await Promise.all([getLocale(), getVerificationDashboard(guildId)]);

  return (
    <div className="space-y-6">
@@ -16,7 +16,11 @@ export default async function VerificationPage({ params }: VerificationPageProps
        <h1 className="text-2xl font-semibold">{t(locale, 'modules.verification.label')}</h1>
        <p className="text-sm text-muted-foreground">{t(locale, 'modules.verification.description')}</p>
      </div>
-      <VerificationForm guildId={guildId} initialValue={config} />
+      <VerificationForm
+        guildId={guildId}
+        initialValue={payload.config}
+        availableCaptchaProviders={payload.availableCaptchaProviders}
+      />
    </div>
  );
 }
--- a/apps/webui/src/app/verify/captcha/route.ts
+++ b/apps/webui/src/app/verify/captcha/route.ts
@@ -1,8 +1,13 @@
 import { NextResponse } from 'next/server';
+import type { CaptchaProvider } from '@nexumi/shared';
 import {
  deleteCaptchaChallenge,
  getCaptchaChallenge,
-  hashCaptchaAnswer
+  getCaptchaPublicConfig,
+  getClientIp,
+  hashCaptchaAnswer,
+  hashClientSignal,
+  verifyProviderToken
 } from '@/lib/captcha';
 import { getVerificationQueue } from '@/lib/queues';

@@ -14,53 +19,120 @@ function escapeHtml(value: string): string {
    .replaceAll('"', '&quot;');
 }

-function renderCaptchaPage(token: string, question: string, error?: string): string {
-  const errorBlock = error ? `<p style="color:#ef4444">${escapeHtml(error)}</p>` : '';
+const PAGE_STYLES = `
+  body { font-family: system-ui, sans-serif; background:#0b1220; color:#f8fafc; display:flex; justify-content:center; align-items:center; min-height:100vh; margin:0; }
+  .card { background:#111827; padding:2rem; border-radius:12px; width:min(440px, 92vw); border:1px solid #1f2937; }
+  h1 { margin:0 0 0.5rem; font-size:1.35rem; }
+  p { margin:0 0 1rem; color:#cbd5e1; line-height:1.45; }
+  .error { color:#f87171; margin-bottom:0.75rem; }
+  input, button { width:100%; padding:0.75rem; margin-top:0.75rem; border-radius:8px; border:1px solid #374151; background:#0b1220; color:#f8fafc; box-sizing:border-box; }
+  button { background:#4f46e5; border:none; cursor:pointer; font-weight:600; }
+  .widget { display:flex; justify-content:center; margin:1rem 0; min-height:78px; }
+`;
+
+function renderShell(body: string): string {
  return `<!DOCTYPE html>
 <html lang="en">
 <head>
  <meta charset="utf-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>Nexumi Verification</title>
-  <style>
-    body { font-family: Inter, system-ui, sans-serif; background:#111827; color:#f9fafb; display:flex; justify-content:center; align-items:center; min-height:100vh; margin:0; }
-    form { background:#1f2937; padding:2rem; border-radius:12px; width:min(420px, 90vw); }
-    input, button { width:100%; padding:0.75rem; margin-top:0.75rem; border-radius:8px; border:1px solid #374151; background:#111827; color:#f9fafb; box-sizing:border-box; }
-    button { background:#6366f1; border:none; cursor:pointer; font-weight:600; }
-  </style>
+  <style>${PAGE_STYLES}</style>
 </head>
-<body>
-  <form method="POST" action="/verify/captcha">
+<body>${body}</body>
+</html>`;
+}
+
+function renderMathPage(token: string, question: string, error?: string): string {
+  const errorBlock = error ? `<p class="error">${escapeHtml(error)}</p>` : '';
+  return renderShell(`
+  <form class="card" method="POST" action="/verify/captcha">
    <h1>Nexumi Verification</h1>
    <p>Solve: <strong>${escapeHtml(question)} = ?</strong></p>
    ${errorBlock}
    <input type="hidden" name="token" value="${escapeHtml(token)}" />
+    <input type="hidden" name="provider" value="MATH" />
    <input type="number" name="answer" required autofocus />
    <button type="submit">Verify</button>
+  </form>`);
+}
+
+function renderProviderPage(
+  token: string,
+  provider: CaptchaProvider,
+  siteKey: string,
+  error?: string
+): string {
+  const errorBlock = error ? `<p class="error">${escapeHtml(error)}</p>` : '';
+  const labels: Record<string, string> = {
+    RECAPTCHA_V2: 'Complete the Google reCAPTCHA below.',
+    RECAPTCHA_V3: 'Checking with Google reCAPTCHA…',
+    HCAPTCHA: 'Complete the hCaptcha below.',
+    TURNSTILE: 'Complete the Cloudflare Turnstile below.'
+  };
+
+  if (provider === 'RECAPTCHA_V3') {
+    return renderShell(`
+  <form class="card" id="verify-form" method="POST" action="/verify/captcha">
+    <h1>Nexumi Verification</h1>
+    <p>${escapeHtml(labels.RECAPTCHA_V3)}</p>
+    ${errorBlock}
+    <input type="hidden" name="token" value="${escapeHtml(token)}" />
+    <input type="hidden" name="provider" value="RECAPTCHA_V3" />
+    <input type="hidden" name="captcha_response" id="captcha_response" />
+    <button type="submit" id="submit-btn" disabled>Verifying…</button>
  </form>
-</body>
-</html>`;
+  <script src="https://www.google.com/recaptcha/api.js?render=${escapeHtml(siteKey)}"></script>
+  <script>
+    grecaptcha.ready(function () {
+      grecaptcha.execute('${escapeHtml(siteKey)}', { action: 'verify' }).then(function (token) {
+        document.getElementById('captcha_response').value = token;
+        document.getElementById('verify-form').submit();
+      });
+    });
+  </script>`);
+  }
+
+  let widget = '';
+  let scripts = '';
+  if (provider === 'RECAPTCHA_V2') {
+    widget = `<div class="g-recaptcha" data-sitekey="${escapeHtml(siteKey)}"></div>`;
+    scripts = `<script src="https://www.google.com/recaptcha/api.js" async defer></script>`;
+  } else if (provider === 'HCAPTCHA') {
+    widget = `<div class="h-captcha" data-sitekey="${escapeHtml(siteKey)}"></div>`;
+    scripts = `<script src="https://js.hcaptcha.com/1/api.js" async defer></script>`;
+  } else if (provider === 'TURNSTILE') {
+    widget = `<div class="cf-turnstile" data-sitekey="${escapeHtml(siteKey)}"></div>`;
+    scripts = `<script src="https://challenges.cloudflare.com/turnstile/v0/api.js" async defer></script>`;
+  }
+
+  return renderShell(`
+  <form class="card" method="POST" action="/verify/captcha">
+    <h1>Nexumi Verification</h1>
+    <p>${escapeHtml(labels[provider] ?? 'Complete the captcha below.')}</p>
+    ${errorBlock}
+    <input type="hidden" name="token" value="${escapeHtml(token)}" />
+    <input type="hidden" name="provider" value="${escapeHtml(provider)}" />
+    <div class="widget">${widget}</div>
+    <button type="submit">Verify</button>
+  </form>
+  ${scripts}`);
+}
+
+function renderMisconfigured(provider: string): string {
+  return renderShell(`
+  <div class="card">
+    <h1>Captcha unavailable</h1>
+    <p>Provider <strong>${escapeHtml(provider)}</strong> is not configured on this server. Ask an admin to set the keys in <code>.env</code>, or switch the guild to Math captcha.</p>
+  </div>`);
 }

 function renderDonePage(): string {
-  return `<!DOCTYPE html>
-<html lang="en">
-<head>
-  <meta charset="utf-8" />
-  <meta name="viewport" content="width=device-width, initial-scale=1" />
-  <title>Nexumi Verified</title>
-  <style>
-    body { font-family: Inter, system-ui, sans-serif; background:#111827; color:#f9fafb; display:flex; justify-content:center; align-items:center; min-height:100vh; margin:0; }
-    div { text-align:center; }
-  </style>
-</head>
-<body>
-  <div>
+  return renderShell(`
+  <div class="card" style="text-align:center">
    <h1>Verified</h1>
    <p>You can return to Discord.</p>
-  </div>
-</body>
-</html>`;
+  </div>`);
 }

 function html(body: string, status = 200): NextResponse {
@@ -70,6 +142,39 @@ function html(body: string, status = 200): NextResponse {
  });
 }

+function extractProviderResponse(form: FormData, provider: CaptchaProvider): string {
+  const direct = String(form.get('captcha_response') ?? '').trim();
+  if (direct) {
+    return direct;
+  }
+  if (provider === 'RECAPTCHA_V2' || provider === 'RECAPTCHA_V3') {
+    return String(form.get('g-recaptcha-response') ?? '').trim();
+  }
+  if (provider === 'HCAPTCHA') {
+    return String(form.get('h-captcha-response') ?? '').trim();
+  }
+  if (provider === 'TURNSTILE') {
+    return String(form.get('cf-turnstile-response') ?? '').trim();
+  }
+  return '';
+}
+
+function renderChallengePage(
+  token: string,
+  provider: CaptchaProvider,
+  question: string | undefined,
+  error?: string
+): NextResponse {
+  if (provider === 'MATH') {
+    return html(renderMathPage(token, question ?? '?', error));
+  }
+  const publicConfig = getCaptchaPublicConfig(provider);
+  if (!publicConfig.siteKey) {
+    return html(renderMisconfigured(provider), 503);
+  }
+  return html(renderProviderPage(token, provider, publicConfig.siteKey, error));
+}
+
 export async function GET(request: Request): Promise<NextResponse> {
  const token = new URL(request.url).searchParams.get('token');
  if (!token) {
@@ -79,14 +184,13 @@ export async function GET(request: Request): Promise<NextResponse> {
  if (!challenge) {
    return new NextResponse('Captcha expired', { status: 404 });
  }
-  return html(renderCaptchaPage(token, challenge.question));
+  return renderChallengePage(token, challenge.provider, challenge.question);
 }

 export async function POST(request: Request): Promise<NextResponse> {
  const form = await request.formData();
  const token = String(form.get('token') ?? '');
-  const answer = String(form.get('answer') ?? '');
-  if (!token || !answer) {
+  if (!token) {
    return new NextResponse('Missing fields', { status: 400 });
  }

@@ -95,14 +199,43 @@ export async function POST(request: Request): Promise<NextResponse> {
    return new NextResponse('Captcha expired', { status: 404 });
  }

-  if (hashCaptchaAnswer(answer) !== challenge.answerHash) {
-    return html(renderCaptchaPage(token, challenge.question, 'Wrong answer. Try again.'));
+  const provider = challenge.provider;
+  const clientIp = getClientIp(request);
+  const userAgent = request.headers.get('user-agent') ?? '';
+
+  if (provider === 'MATH') {
+    const answer = String(form.get('answer') ?? '');
+    if (!answer || !challenge.answerHash || hashCaptchaAnswer(answer) !== challenge.answerHash) {
+      return renderChallengePage(token, provider, challenge.question, 'Wrong answer. Try again.');
+    }
+  } else {
+    const responseToken = extractProviderResponse(form, provider);
+    const verified = await verifyProviderToken(provider, responseToken, clientIp);
+    if (!verified.ok) {
+      const message =
+        verified.error === 'score_too_low'
+          ? 'reCAPTCHA score too low. Try again.'
+          : verified.error === 'provider_not_configured'
+            ? 'Captcha provider is not configured.'
+            : 'Captcha failed. Try again.';
+      return renderChallengePage(token, provider, challenge.question, message);
+    }
  }

  await deleteCaptchaChallenge(token);
+
+  const ipHash = clientIp ? hashClientSignal(clientIp) : null;
+  const userAgentHash = userAgent ? hashClientSignal(userAgent) : null;
+
  await getVerificationQueue().add(
    'verificationComplete',
-    { guildId: challenge.guildId, userId: challenge.userId },
+    {
+      guildId: challenge.guildId,
+      userId: challenge.userId,
+      ipHash,
+      userAgentHash,
+      captchaProvider: provider
+    },
    { removeOnComplete: 1000, removeOnFail: 500 }
  );

--- a/apps/webui/src/components/modules/verification-form.tsx
+++ b/apps/webui/src/components/modules/verification-form.tsx
@@ -1,6 +1,6 @@
 'use client';

-import type { VerificationConfigDashboard } from '@nexumi/shared';
+import type { CaptchaProvider, VerificationConfigDashboard } from '@nexumi/shared';
 import { FieldAnchor } from '@/components/layout/field-anchor';
 import { useTranslations } from '@/components/locale-provider';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
@@ -33,9 +33,14 @@ async function saveVerification(guildId: string, value: VerificationConfigDashbo
 interface VerificationFormProps {
  guildId: string;
  initialValue: VerificationConfigDashboard;
+  availableCaptchaProviders: CaptchaProvider[];
 }

-export function VerificationForm({ guildId, initialValue }: VerificationFormProps) {
+export function VerificationForm({
+  guildId,
+  initialValue,
+  availableCaptchaProviders
+}: VerificationFormProps) {
  const t = useTranslations();

  return (
@@ -44,113 +49,249 @@ export function VerificationForm({ guildId, initialValue }: VerificationFormProp
      onSave={(value) => saveVerification(guildId, value)}
    >
      {({ value, setValue }) => (
-        <Card>
-          <CardHeader>
-            <CardTitle>{t('modulePages.verification.title')}</CardTitle>
-            <CardDescription>{t('modulePages.verification.description')}</CardDescription>
-          </CardHeader>
-          <CardContent className="space-y-4">
-            <FieldAnchor id="field-verify-enabled">
-            <div className="flex items-center justify-between rounded-md border border-border p-4">
-              <Label>{t('modulePages.verification.enabledLabel')}</Label>
-              <Switch
-                checked={value.enabled}
-                onCheckedChange={(checked) => setValue((prev) => ({ ...prev, enabled: checked }))}
-              />
-            </div>
-            </FieldAnchor>
+        <div className="space-y-4">
+          <Card>
+            <CardHeader>
+              <CardTitle>{t('modulePages.verification.title')}</CardTitle>
+              <CardDescription>{t('modulePages.verification.description')}</CardDescription>
+            </CardHeader>
+            <CardContent className="space-y-4">
+              <FieldAnchor id="field-verify-enabled">
+                <div className="flex items-center justify-between rounded-md border border-border p-4">
+                  <Label>{t('modulePages.verification.enabledLabel')}</Label>
+                  <Switch
+                    checked={value.enabled}
+                    onCheckedChange={(checked) => setValue((prev) => ({ ...prev, enabled: checked }))}
+                  />
+                </div>
+              </FieldAnchor>

-            <div className="grid gap-4 sm:grid-cols-2">
-              <FieldAnchor id="field-verify-mode">
-              <div className="space-y-2">
-                <Label>{t('modulePages.verification.mode')}</Label>
-                <Select
-                  value={value.mode}
-                  onValueChange={(mode) =>
-                    setValue((prev) => ({ ...prev, mode: mode as VerificationConfigDashboard['mode'] }))
-                  }
-                >
-                  <SelectTrigger>
-                    <SelectValue />
-                  </SelectTrigger>
-                  <SelectContent>
-                    <SelectItem value="BUTTON">{t('modulePages.verification.modes.BUTTON')}</SelectItem>
-                    <SelectItem value="CAPTCHA">{t('modulePages.verification.modes.CAPTCHA')}</SelectItem>
-                  </SelectContent>
-                </Select>
+              <div className="grid gap-4 sm:grid-cols-2">
+                <FieldAnchor id="field-verify-mode">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.mode')}</Label>
+                    <Select
+                      value={value.mode}
+                      onValueChange={(mode) =>
+                        setValue((prev) => ({ ...prev, mode: mode as VerificationConfigDashboard['mode'] }))
+                      }
+                    >
+                      <SelectTrigger>
+                        <SelectValue />
+                      </SelectTrigger>
+                      <SelectContent>
+                        <SelectItem value="BUTTON">{t('modulePages.verification.modes.BUTTON')}</SelectItem>
+                        <SelectItem value="CAPTCHA">{t('modulePages.verification.modes.CAPTCHA')}</SelectItem>
+                      </SelectContent>
+                    </Select>
+                  </div>
+                </FieldAnchor>
+                <FieldAnchor id="field-verify-fail">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.failAction')}</Label>
+                    <Select
+                      value={value.failAction}
+                      onValueChange={(failAction) =>
+                        setValue((prev) => ({
+                          ...prev,
+                          failAction: failAction as VerificationConfigDashboard['failAction']
+                        }))
+                      }
+                    >
+                      <SelectTrigger>
+                        <SelectValue />
+                      </SelectTrigger>
+                      <SelectContent>
+                        <SelectItem value="KICK">{t('modulePages.verification.failActions.KICK')}</SelectItem>
+                        <SelectItem value="BAN">{t('modulePages.verification.failActions.BAN')}</SelectItem>
+                        <SelectItem value="NONE">{t('modulePages.verification.failActions.NONE')}</SelectItem>
+                      </SelectContent>
+                    </Select>
+                  </div>
+                </FieldAnchor>
              </div>
-              </FieldAnchor>
-              <FieldAnchor id="field-verify-fail">
-              <div className="space-y-2">
-                <Label>{t('modulePages.verification.failAction')}</Label>
-                <Select
-                  value={value.failAction}
-                  onValueChange={(failAction) =>
-                    setValue((prev) => ({ ...prev, failAction: failAction as VerificationConfigDashboard['failAction'] }))
-                  }
-                >
-                  <SelectTrigger>
-                    <SelectValue />
-                  </SelectTrigger>
-                  <SelectContent>
-                    <SelectItem value="KICK">{t('modulePages.verification.failActions.KICK')}</SelectItem>
-                    <SelectItem value="BAN">{t('modulePages.verification.failActions.BAN')}</SelectItem>
-                    <SelectItem value="NONE">{t('modulePages.verification.failActions.NONE')}</SelectItem>
-                  </SelectContent>
-                </Select>
-              </div>
-              </FieldAnchor>
-            </div>

-            <div className="grid gap-4 sm:grid-cols-3">
-              <FieldAnchor id="field-verify-channel">
-              <div className="space-y-2">
-                <Label>{t('modulePages.verification.channelId')}</Label>
-                <DiscordChannelSelect
-                  guildId={guildId}
-                  value={value.channelId}
-                  onChange={(channelId) => setValue((prev) => ({ ...prev, channelId }))}
-                />
-              </div>
-              </FieldAnchor>
-              <FieldAnchor id="field-verify-role">
-              <div className="space-y-2">
-                <Label>{t('modulePages.verification.verifiedRoleId')}</Label>
-                <DiscordRoleSelect
-                  guildId={guildId}
-                  value={value.verifiedRoleId}
-                  onChange={(verifiedRoleId) => setValue((prev) => ({ ...prev, verifiedRoleId }))}
-                />
-              </div>
-              </FieldAnchor>
-              <FieldAnchor id="field-verify-unverified">
-              <div className="space-y-2">
-                <Label>{t('modulePages.verification.unverifiedRoleId')}</Label>
-                <DiscordRoleSelect
-                  guildId={guildId}
-                  value={value.unverifiedRoleId}
-                  onChange={(unverifiedRoleId) => setValue((prev) => ({ ...prev, unverifiedRoleId }))}
-                />
-              </div>
-              </FieldAnchor>
-            </div>
+              {value.mode === 'CAPTCHA' ? (
+                <FieldAnchor id="field-verify-captcha-provider">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.captchaProvider')}</Label>
+                    <Select
+                      value={value.captchaProvider}
+                      onValueChange={(captchaProvider) =>
+                        setValue((prev) => ({
+                          ...prev,
+                          captchaProvider: captchaProvider as CaptchaProvider
+                        }))
+                      }
+                    >
+                      <SelectTrigger>
+                        <SelectValue />
+                      </SelectTrigger>
+                      <SelectContent>
+                        {availableCaptchaProviders.map((provider) => (
+                          <SelectItem key={provider} value={provider}>
+                            {t(`modulePages.verification.captchaProviders.${provider}`)}
+                          </SelectItem>
+                        ))}
+                      </SelectContent>
+                    </Select>
+                    <p className="text-xs text-muted-foreground">
+                      {t('modulePages.verification.captchaProviderHint')}
+                    </p>
+                  </div>
+                </FieldAnchor>
+              ) : null}

-            <FieldAnchor id="field-verify-age">
-            <div className="space-y-2">
-              <Label>{t('modulePages.verification.minAccountAgeDays')}</Label>
-              <Input
-                type="number"
-                min={0}
-                className="w-40"
-                value={value.minAccountAgeDays}
-                onChange={(event) =>
-                  setValue((prev) => ({ ...prev, minAccountAgeDays: Number(event.target.value) || 0 }))
-                }
-              />
-            </div>
-            </FieldAnchor>
-          </CardContent>
-        </Card>
+              <div className="grid gap-4 sm:grid-cols-3">
+                <FieldAnchor id="field-verify-channel">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.channelId')}</Label>
+                    <DiscordChannelSelect
+                      guildId={guildId}
+                      value={value.channelId}
+                      onChange={(channelId) => setValue((prev) => ({ ...prev, channelId }))}
+                    />
+                  </div>
+                </FieldAnchor>
+                <FieldAnchor id="field-verify-role">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.verifiedRoleId')}</Label>
+                    <DiscordRoleSelect
+                      guildId={guildId}
+                      value={value.verifiedRoleId}
+                      onChange={(verifiedRoleId) => setValue((prev) => ({ ...prev, verifiedRoleId }))}
+                    />
+                  </div>
+                </FieldAnchor>
+                <FieldAnchor id="field-verify-unverified">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.unverifiedRoleId')}</Label>
+                    <DiscordRoleSelect
+                      guildId={guildId}
+                      value={value.unverifiedRoleId}
+                      onChange={(unverifiedRoleId) =>
+                        setValue((prev) => ({ ...prev, unverifiedRoleId }))
+                      }
+                    />
+                  </div>
+                </FieldAnchor>
+              </div>
+
+              <FieldAnchor id="field-verify-age">
+                <div className="space-y-2">
+                  <Label>{t('modulePages.verification.minAccountAgeDays')}</Label>
+                  <Input
+                    type="number"
+                    min={0}
+                    className="w-40"
+                    value={value.minAccountAgeDays}
+                    onChange={(event) =>
+                      setValue((prev) => ({
+                        ...prev,
+                        minAccountAgeDays: Number(event.target.value) || 0
+                      }))
+                    }
+                  />
+                </div>
+              </FieldAnchor>
+            </CardContent>
+          </Card>
+
+          <Card>
+            <CardHeader>
+              <CardTitle>{t('modulePages.verification.altTitle')}</CardTitle>
+              <CardDescription>{t('modulePages.verification.altDescription')}</CardDescription>
+            </CardHeader>
+            <CardContent className="space-y-4">
+              <FieldAnchor id="field-verify-alt-enabled">
+                <div className="flex items-center justify-between rounded-md border border-border p-4">
+                  <Label>{t('modulePages.verification.altDetectionEnabled')}</Label>
+                  <Switch
+                    checked={value.altDetectionEnabled}
+                    onCheckedChange={(checked) =>
+                      setValue((prev) => ({ ...prev, altDetectionEnabled: checked }))
+                    }
+                  />
+                </div>
+              </FieldAnchor>
+
+              <FieldAnchor id="field-verify-alt-block">
+                <div className="flex items-center justify-between rounded-md border border-border p-4">
+                  <div className="space-y-1 pr-4">
+                    <Label>{t('modulePages.verification.altBlockOnMatch')}</Label>
+                    <p className="text-xs text-muted-foreground">
+                      {t('modulePages.verification.altBlockOnMatchHint')}
+                    </p>
+                  </div>
+                  <Switch
+                    checked={value.altBlockOnMatch}
+                    onCheckedChange={(checked) =>
+                      setValue((prev) => ({ ...prev, altBlockOnMatch: checked }))
+                    }
+                    disabled={!value.altDetectionEnabled}
+                  />
+                </div>
+              </FieldAnchor>
+
+              <div className="grid gap-4 sm:grid-cols-3">
+                <FieldAnchor id="field-verify-alt-ip-days">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.altIpWindowDays')}</Label>
+                    <Input
+                      type="number"
+                      min={1}
+                      max={365}
+                      value={value.altIpWindowDays}
+                      disabled={!value.altDetectionEnabled}
+                      onChange={(event) =>
+                        setValue((prev) => ({
+                          ...prev,
+                          altIpWindowDays: Number(event.target.value) || 1
+                        }))
+                      }
+                    />
+                  </div>
+                </FieldAnchor>
+                <FieldAnchor id="field-verify-alt-invite-hours">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.altInviteWindowHours')}</Label>
+                    <Input
+                      type="number"
+                      min={1}
+                      max={720}
+                      value={value.altInviteWindowHours}
+                      disabled={!value.altDetectionEnabled}
+                      onChange={(event) =>
+                        setValue((prev) => ({
+                          ...prev,
+                          altInviteWindowHours: Number(event.target.value) || 1
+                        }))
+                      }
+                    />
+                  </div>
+                </FieldAnchor>
+                <FieldAnchor id="field-verify-alt-max-invite">
+                  <div className="space-y-2">
+                    <Label>{t('modulePages.verification.altMaxAccountsPerInvite')}</Label>
+                    <Input
+                      type="number"
+                      min={1}
+                      max={50}
+                      value={value.altMaxAccountsPerInvite}
+                      disabled={!value.altDetectionEnabled}
+                      onChange={(event) =>
+                        setValue((prev) => ({
+                          ...prev,
+                          altMaxAccountsPerInvite: Number(event.target.value) || 1
+                        }))
+                      }
+                    />
+                  </div>
+                </FieldAnchor>
+              </div>
+            </CardContent>
+          </Card>
+        </div>
      )}
    </SettingsForm>
  );
--- a/apps/webui/src/lib/captcha.ts
+++ b/apps/webui/src/lib/captcha.ts
@@ -1,5 +1,7 @@
 import { createHash } from 'node:crypto';
+import type { CaptchaProvider } from '@nexumi/shared';
 import { redis } from './redis';
+import { env } from './env';

 const CAPTCHA_PREFIX = 'verify:captcha:';

@@ -7,8 +9,9 @@ export type CaptchaChallenge = {
  token: string;
  guildId: string;
  userId: string;
-  question: string;
-  answerHash: string;
+  provider: CaptchaProvider;
+  question?: string;
+  answerHash?: string;
 };

 export async function getCaptchaChallenge(token: string): Promise<CaptchaChallenge | null> {
@@ -17,7 +20,11 @@ export async function getCaptchaChallenge(token: string): Promise<CaptchaChallen
    return null;
  }
  try {
-    return JSON.parse(raw) as CaptchaChallenge;
+    const parsed = JSON.parse(raw) as CaptchaChallenge;
+    if (!parsed.provider) {
+      parsed.provider = 'MATH';
+    }
+    return parsed;
  } catch {
    return null;
  }
@@ -30,3 +37,176 @@ export async function deleteCaptchaChallenge(token: string): Promise<void> {
 export function hashCaptchaAnswer(answer: string): string {
  return createHash('sha256').update(answer.trim()).digest('hex');
 }
+
+export function hashClientSignal(value: string): string | null {
+  const salt = env.CAPTCHA_IP_HASH_SALT;
+  if (!salt || !value) {
+    return null;
+  }
+  return createHash('sha256').update(`${salt}:${value}`).digest('hex');
+}
+
+export function getClientIp(request: Request): string | null {
+  const forwarded = request.headers.get('x-forwarded-for');
+  if (forwarded) {
+    const first = forwarded.split(',')[0]?.trim();
+    if (first) {
+      return first;
+    }
+  }
+  const realIp = request.headers.get('x-real-ip')?.trim();
+  return realIp || null;
+}
+
+export type CaptchaPublicConfig = {
+  provider: CaptchaProvider;
+  siteKey: string | null;
+  recaptchaV3MinScore: number;
+};
+
+export function getAvailableCaptchaProviders(): CaptchaProvider[] {
+  const providers: CaptchaProvider[] = ['MATH'];
+  if (env.RECAPTCHA_SITE_KEY && env.RECAPTCHA_SECRET_KEY) {
+    providers.push('RECAPTCHA_V2');
+  }
+  const v3Site = env.RECAPTCHA_V3_SITE_KEY ?? env.RECAPTCHA_SITE_KEY;
+  const v3Secret = env.RECAPTCHA_V3_SECRET_KEY ?? env.RECAPTCHA_SECRET_KEY;
+  if (v3Site && v3Secret) {
+    providers.push('RECAPTCHA_V3');
+  }
+  if (env.HCAPTCHA_SITE_KEY && env.HCAPTCHA_SECRET_KEY) {
+    providers.push('HCAPTCHA');
+  }
+  if (env.TURNSTILE_SITE_KEY && env.TURNSTILE_SECRET_KEY) {
+    providers.push('TURNSTILE');
+  }
+  return providers;
+}
+
+export function getCaptchaPublicConfig(provider: CaptchaProvider): CaptchaPublicConfig {
+  switch (provider) {
+    case 'RECAPTCHA_V2':
+      return {
+        provider,
+        siteKey: env.RECAPTCHA_SITE_KEY ?? null,
+        recaptchaV3MinScore: env.RECAPTCHA_V3_MIN_SCORE
+      };
+    case 'RECAPTCHA_V3':
+      return {
+        provider,
+        siteKey: env.RECAPTCHA_V3_SITE_KEY ?? env.RECAPTCHA_SITE_KEY ?? null,
+        recaptchaV3MinScore: env.RECAPTCHA_V3_MIN_SCORE
+      };
+    case 'HCAPTCHA':
+      return {
+        provider,
+        siteKey: env.HCAPTCHA_SITE_KEY ?? null,
+        recaptchaV3MinScore: env.RECAPTCHA_V3_MIN_SCORE
+      };
+    case 'TURNSTILE':
+      return {
+        provider,
+        siteKey: env.TURNSTILE_SITE_KEY ?? null,
+        recaptchaV3MinScore: env.RECAPTCHA_V3_MIN_SCORE
+      };
+    default:
+      return { provider: 'MATH', siteKey: null, recaptchaV3MinScore: env.RECAPTCHA_V3_MIN_SCORE };
+  }
+}
+
+type SiteVerifyResult = { success: boolean; score?: number; 'error-codes'?: string[] };
+
+async function postSiteVerify(
+  url: string,
+  secret: string,
+  responseToken: string,
+  remoteip?: string | null
+): Promise<SiteVerifyResult> {
+  const body = new URLSearchParams();
+  body.set('secret', secret);
+  body.set('response', responseToken);
+  if (remoteip) {
+    body.set('remoteip', remoteip);
+  }
+  const res = await fetch(url, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body
+  });
+  if (!res.ok) {
+    return { success: false, 'error-codes': [`http_${res.status}`] };
+  }
+  return (await res.json()) as SiteVerifyResult;
+}
+
+export async function verifyProviderToken(
+  provider: CaptchaProvider,
+  responseToken: string,
+  remoteip?: string | null
+): Promise<{ ok: boolean; error?: string }> {
+  if (!responseToken.trim()) {
+    return { ok: false, error: 'missing_token' };
+  }
+
+  if (provider === 'RECAPTCHA_V2') {
+    if (!env.RECAPTCHA_SECRET_KEY) {
+      return { ok: false, error: 'provider_not_configured' };
+    }
+    const result = await postSiteVerify(
+      'https://www.google.com/recaptcha/api/siteverify',
+      env.RECAPTCHA_SECRET_KEY,
+      responseToken,
+      remoteip
+    );
+    return result.success ? { ok: true } : { ok: false, error: 'provider_rejected' };
+  }
+
+  if (provider === 'RECAPTCHA_V3') {
+    const secret = env.RECAPTCHA_V3_SECRET_KEY ?? env.RECAPTCHA_SECRET_KEY;
+    if (!secret) {
+      return { ok: false, error: 'provider_not_configured' };
+    }
+    const result = await postSiteVerify(
+      'https://www.google.com/recaptcha/api/siteverify',
+      secret,
+      responseToken,
+      remoteip
+    );
+    if (!result.success) {
+      return { ok: false, error: 'provider_rejected' };
+    }
+    const score = result.score ?? 0;
+    if (score < env.RECAPTCHA_V3_MIN_SCORE) {
+      return { ok: false, error: 'score_too_low' };
+    }
+    return { ok: true };
+  }
+
+  if (provider === 'HCAPTCHA') {
+    if (!env.HCAPTCHA_SECRET_KEY) {
+      return { ok: false, error: 'provider_not_configured' };
+    }
+    const result = await postSiteVerify(
+      'https://hcaptcha.com/siteverify',
+      env.HCAPTCHA_SECRET_KEY,
+      responseToken,
+      remoteip
+    );
+    return result.success ? { ok: true } : { ok: false, error: 'provider_rejected' };
+  }
+
+  if (provider === 'TURNSTILE') {
+    if (!env.TURNSTILE_SECRET_KEY) {
+      return { ok: false, error: 'provider_not_configured' };
+    }
+    const result = await postSiteVerify(
+      'https://challenges.cloudflare.com/turnstile/v0/siteverify',
+      env.TURNSTILE_SECRET_KEY,
+      responseToken,
+      remoteip
+    );
+    return result.success ? { ok: true } : { ok: false, error: 'provider_rejected' };
+  }
+
+  return { ok: false, error: 'unsupported_provider' };
+}
--- a/apps/webui/src/lib/dashboard-search-index.ts
+++ b/apps/webui/src/lib/dashboard-search-index.ts
@@ -379,6 +379,48 @@ export const SETTINGS_SEARCH_FIELDS: SearchIndexEntry[] = [
    href: 'verification',
    hash: 'field-verify-age'
  },
+  {
+    id: 'setting-verify-captcha-provider',
+    kind: 'setting',
+    labelKey: 'modulePages.verification.captchaProvider',
+    href: 'verification',
+    hash: 'field-verify-captcha-provider'
+  },
+  {
+    id: 'setting-verify-alt-enabled',
+    kind: 'setting',
+    labelKey: 'modulePages.verification.altDetectionEnabled',
+    href: 'verification',
+    hash: 'field-verify-alt-enabled'
+  },
+  {
+    id: 'setting-verify-alt-block',
+    kind: 'setting',
+    labelKey: 'modulePages.verification.altBlockOnMatch',
+    href: 'verification',
+    hash: 'field-verify-alt-block'
+  },
+  {
+    id: 'setting-verify-alt-ip-days',
+    kind: 'setting',
+    labelKey: 'modulePages.verification.altIpWindowDays',
+    href: 'verification',
+    hash: 'field-verify-alt-ip-days'
+  },
+  {
+    id: 'setting-verify-alt-invite-hours',
+    kind: 'setting',
+    labelKey: 'modulePages.verification.altInviteWindowHours',
+    href: 'verification',
+    hash: 'field-verify-alt-invite-hours'
+  },
+  {
+    id: 'setting-verify-alt-max-invite',
+    kind: 'setting',
+    labelKey: 'modulePages.verification.altMaxAccountsPerInvite',
+    href: 'verification',
+    hash: 'field-verify-alt-max-invite'
+  },
  // Leveling
  {
    id: 'setting-leveling-enabled',
--- a/apps/webui/src/lib/env.ts
+++ b/apps/webui/src/lib/env.ts
@@ -35,7 +35,20 @@ const EnvSchema = z.object({
  LEGAL_OPERATOR_NAME: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
  LEGAL_OPERATOR_ADDRESS: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
  LEGAL_OPERATOR_EMAIL: z.preprocess(emptyToUndefined, z.string().email().optional()),
-  LEGAL_OPERATOR_PHONE: z.preprocess(emptyToUndefined, z.string().min(1).optional())
+  LEGAL_OPERATOR_PHONE: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+
+  // Captcha providers (site keys are public; secrets stay server-side)
+  RECAPTCHA_SITE_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  RECAPTCHA_SECRET_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  RECAPTCHA_V3_SITE_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  RECAPTCHA_V3_SECRET_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  RECAPTCHA_V3_MIN_SCORE: z.coerce.number().min(0).max(1).default(0.5),
+  HCAPTCHA_SITE_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  HCAPTCHA_SECRET_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  TURNSTILE_SITE_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  TURNSTILE_SECRET_KEY: z.preprocess(emptyToUndefined, z.string().min(1).optional()),
+  /// Shared with bot for alt-account IP hashing (min 16 chars).
+  CAPTCHA_IP_HASH_SALT: z.preprocess(emptyToUndefined, z.string().min(16).optional())
 });

 export const env = EnvSchema.parse(process.env);
--- a/apps/webui/src/lib/module-configs/verification.ts
+++ b/apps/webui/src/lib/module-configs/verification.ts
@@ -1,6 +1,7 @@
-import type { VerificationConfigDashboard, VerificationConfigDashboardPatch } from '@nexumi/shared';
+import type { CaptchaProvider, VerificationConfigDashboard, VerificationConfigDashboardPatch } from '@nexumi/shared';
 import type { Prisma } from '@prisma/client';
 import { prisma } from '../prisma';
+import { getAvailableCaptchaProviders } from '../captcha';

 async function ensureVerificationConfig(guildId: string) {
  await prisma.guild.upsert({ where: { id: guildId }, update: {}, create: { id: guildId } });
@@ -11,21 +12,39 @@ async function ensureVerificationConfig(guildId: string) {
  });
 }

-function toDashboard(config: Awaited<ReturnType<typeof ensureVerificationConfig>>): VerificationConfigDashboard {
+function toDashboard(
+  config: Awaited<ReturnType<typeof ensureVerificationConfig>>,
+  available: CaptchaProvider[]
+): VerificationConfigDashboard {
+  const rawProvider = (config.captchaProvider as CaptchaProvider) ?? 'MATH';
+  const captchaProvider = available.includes(rawProvider) ? rawProvider : 'MATH';
  return {
    enabled: config.enabled,
    channelId: config.channelId ?? '',
    verifiedRoleId: config.verifiedRoleId ?? '',
    unverifiedRoleId: config.unverifiedRoleId ?? '',
    mode: config.mode as VerificationConfigDashboard['mode'],
+    captchaProvider,
    minAccountAgeDays: config.minAccountAgeDays,
-    failAction: config.failAction as VerificationConfigDashboard['failAction']
+    failAction: config.failAction as VerificationConfigDashboard['failAction'],
+    altDetectionEnabled: config.altDetectionEnabled,
+    altBlockOnMatch: config.altBlockOnMatch,
+    altIpWindowDays: config.altIpWindowDays,
+    altInviteWindowHours: config.altInviteWindowHours,
+    altMaxAccountsPerInvite: config.altMaxAccountsPerInvite
  };
 }

-export async function getVerificationDashboard(guildId: string): Promise<VerificationConfigDashboard> {
+export async function getVerificationDashboard(guildId: string): Promise<{
+  config: VerificationConfigDashboard;
+  availableCaptchaProviders: CaptchaProvider[];
+}> {
  const config = await ensureVerificationConfig(guildId);
-  return toDashboard(config);
+  const availableCaptchaProviders = getAvailableCaptchaProviders();
+  return {
+    config: toDashboard(config, availableCaptchaProviders),
+    availableCaptchaProviders
+  };
 }

 export async function updateVerificationDashboard(
@@ -34,6 +53,11 @@ export async function updateVerificationDashboard(
 ): Promise<VerificationConfigDashboard> {
  await ensureVerificationConfig(guildId);

+  const available = new Set(getAvailableCaptchaProviders());
+  if (patch.captchaProvider !== undefined && !available.has(patch.captchaProvider)) {
+    throw new Error(`Captcha provider ${patch.captchaProvider} is not configured in .env`);
+  }
+
  const { channelId, verifiedRoleId, unverifiedRoleId, ...rest } = patch;
  const data: Prisma.VerificationConfigUpdateInput = { ...rest };
  if (channelId !== undefined) {
@@ -47,5 +71,5 @@ export async function updateVerificationDashboard(
  }

  const updated = await prisma.verificationConfig.update({ where: { guildId }, data });
-  return toDashboard(updated);
+  return toDashboard(updated, getAvailableCaptchaProviders());
 }
--- a/apps/webui/src/messages/de.json
+++ b/apps/webui/src/messages/de.json
@@ -477,6 +477,15 @@
        "BUTTON": "Button",
        "CAPTCHA": "Captcha (WebUI)"
      },
+      "captchaProvider": "Captcha-Anbieter",
+      "captchaProviderHint": "Anbieter mit fehlenden .env-Keys erscheinen nicht in der Liste. Google-Keys: RECAPTCHA_SITE_KEY / RECAPTCHA_SECRET_KEY.",
+      "captchaProviders": {
+        "MATH": "Mathe-Aufgabe",
+        "RECAPTCHA_V2": "Google reCAPTCHA v2",
+        "RECAPTCHA_V3": "Google reCAPTCHA v3",
+        "HCAPTCHA": "hCaptcha",
+        "TURNSTILE": "Cloudflare Turnstile"
+      },
      "failAction": "Aktion bei Fehlschlag",
      "failActions": {
        "KICK": "Kick",
@@ -486,7 +495,15 @@
      "channelId": "Verifizierungs-Kanal",
      "verifiedRoleId": "Rolle nach Verifizierung",
      "unverifiedRoleId": "Rolle vor Verifizierung",
-      "minAccountAgeDays": "Mindest-Accountalter (Tage)"
+      "minAccountAgeDays": "Mindest-Accountalter (Tage)",
+      "altTitle": "Alt-Account-Erkennung",
+      "altDescription": "Erkennt mögliche Zweitaccounts über gemeinsame Captcha-IP (gesalzen gehasht) und Invite-Cluster. Kein Browser-Fingerprinting.",
+      "altDetectionEnabled": "Alt-Erkennung aktivieren",
+      "altBlockOnMatch": "Bei Treffer blockieren",
+      "altBlockOnMatchHint": "Nutzt die konfigurierte Fehlschlag-Aktion (Kick/Ban/Keine). Aus = nur markieren, trotzdem verifizieren.",
+      "altIpWindowDays": "IP-Fenster (Tage)",
+      "altInviteWindowHours": "Invite-Cluster-Fenster (Stunden)",
+      "altMaxAccountsPerInvite": "Max. Accounts pro Invite (Cluster)"
    },
    "leveling": {
      "title": "Leveling & XP",
--- a/apps/webui/src/messages/en.json
+++ b/apps/webui/src/messages/en.json
@@ -477,6 +477,15 @@
        "BUTTON": "Button",
        "CAPTCHA": "Captcha (WebUI)"
      },
+      "captchaProvider": "Captcha provider",
+      "captchaProviderHint": "Providers without .env keys are hidden. Google keys: RECAPTCHA_SITE_KEY / RECAPTCHA_SECRET_KEY.",
+      "captchaProviders": {
+        "MATH": "Math challenge",
+        "RECAPTCHA_V2": "Google reCAPTCHA v2",
+        "RECAPTCHA_V3": "Google reCAPTCHA v3",
+        "HCAPTCHA": "hCaptcha",
+        "TURNSTILE": "Cloudflare Turnstile"
+      },
      "failAction": "Action on failure",
      "failActions": {
        "KICK": "Kick",
@@ -486,7 +495,15 @@
      "channelId": "Verification channel",
      "verifiedRoleId": "Role after verification",
      "unverifiedRoleId": "Role before verification",
-      "minAccountAgeDays": "Minimum account age (days)"
+      "minAccountAgeDays": "Minimum account age (days)",
+      "altTitle": "Alt-account detection",
+      "altDescription": "Flags likely alternate accounts via shared captcha IP (salted hash) and invite clustering. No browser fingerprinting.",
+      "altDetectionEnabled": "Enable alt detection",
+      "altBlockOnMatch": "Block on match",
+      "altBlockOnMatchHint": "Uses the configured fail action (Kick/Ban/None). Off = flag only, still verify.",
+      "altIpWindowDays": "IP window (days)",
+      "altInviteWindowHours": "Invite cluster window (hours)",
+      "altMaxAccountsPerInvite": "Max accounts per invite (cluster)"
    },
    "leveling": {
      "title": "Leveling & XP",
--- a/docs/PHASE-TRACKING.md
+++ b/docs/PHASE-TRACKING.md
@@ -220,6 +220,30 @@
 - Premium-Zahlungsanbindung
 - P4-UX (Server-Lock, Ban deleteMessageSeconds) bewusst nachgelagert

+## Post-Phase – Verification Captcha-Anbieter + Alt-Erkennung (Status: implementiert)
+
+### Abgeschlossen (Code)
+
+- Captcha-Anbieter wählbar pro Guild: `MATH`, `RECAPTCHA_V2`, `RECAPTCHA_V3`, `HCAPTCHA`, `TURNSTILE`
+- Google/hCaptcha/Turnstile Keys in `.env` (WebUI); Dashboard zeigt nur konfigurierte Anbieter
+- Captcha-Seite `/verify/captcha` mit Provider-Widgets; Server-side Siteverify
+- Alt-Account-Erkennung: gesalzener IP-Hash (Captcha-Flow) + Invite-Cluster; optional blockieren via `failAction`
+- Prisma `VerificationRecord` + Config-Felder; Migration `20260723120000_verification_captcha_alt`
+- Slash `/verify setup`: `captcha_provider`, `alt_detection`
+
+### Manuell testen
+
+- [ ] `.env`: `RECAPTCHA_SITE_KEY`/`SECRET` setzen → Dashboard zeigt reCAPTCHA v2/v3
+- [ ] Guild Captcha-Modus + Anbieter wählen → Verify-Button → WebUI Captcha → Rolle
+- [ ] Alt-Erkennung an: zweiter Account gleiche IP → Kick/Ban je nach failAction
+- [ ] Migration: `prisma migrate deploy` + Bot/WebUI neu bauen
+- [ ] `CAPTCHA_IP_HASH_SALT` gesetzt (min. 16 Zeichen), sonst keine IP-Alt-Signale
+
+### Bewusst offen
+
+- Kein Browser-Fingerprinting (DSGVO); IP nur gehasht mit Salt
+- Keine manuelle „Alt freigeben“-UI (nur Flag in `VerificationRecord`)
+
 ## Nächster geplanter Schritt

 - Deploy auf Traefik-Server manuell verifizieren; danach ggf. `deploy` → `main` mergen (nur auf Freigabe).
--- a/packages/shared/src/command-locales.ts
+++ b/packages/shared/src/command-locales.ts
@@ -259,6 +259,10 @@ export const commandLocales = {
    de: 'Verifizierungsmodus',
    en: 'Verification mode'
  },
+  'verify.setup.options.captcha_provider': {
+    de: 'Captcha-Anbieter (nur bei Captcha-Modus)',
+    en: 'Captcha provider (captcha mode only)'
+  },
  'verify.setup.options.min_account_age_days': {
    de: 'Mindest-Accountalter in Tagen',
    en: 'Minimum account age in days'
@@ -267,6 +271,10 @@ export const commandLocales = {
    de: 'Aktion bei Fehlschlag',
    en: 'Action on failure'
  },
+  'verify.setup.options.alt_detection': {
+    de: 'Alt-Account-Erkennung aktivieren',
+    en: 'Enable alt-account detection'
+  },
  'verify.panel.description': {
    de: 'Verifizierungs-Panel posten',
    en: 'Post verification panel'
--- a/packages/shared/src/dashboard.ts
+++ b/packages/shared/src/dashboard.ts
@@ -235,6 +235,13 @@ export type WelcomeConfigDashboardPatch = z.infer<typeof WelcomeConfigDashboardP

 export const VerificationModeDashboardSchema = z.enum(['BUTTON', 'CAPTCHA']);
 export const VerificationFailActionDashboardSchema = z.enum(['KICK', 'BAN', 'NONE']);
+export const CaptchaProviderDashboardSchema = z.enum([
+  'MATH',
+  'RECAPTCHA_V2',
+  'RECAPTCHA_V3',
+  'HCAPTCHA',
+  'TURNSTILE'
+]);

 export const VerificationConfigDashboardSchema = z.object({
  enabled: z.boolean(),
@@ -242,8 +249,14 @@ export const VerificationConfigDashboardSchema = z.object({
  verifiedRoleId: OptionalSnowflakeSchema,
  unverifiedRoleId: OptionalSnowflakeSchema,
  mode: VerificationModeDashboardSchema,
+  captchaProvider: CaptchaProviderDashboardSchema,
  minAccountAgeDays: z.number().int().nonnegative(),
-  failAction: VerificationFailActionDashboardSchema
+  failAction: VerificationFailActionDashboardSchema,
+  altDetectionEnabled: z.boolean(),
+  altBlockOnMatch: z.boolean(),
+  altIpWindowDays: z.number().int().min(1).max(365),
+  altInviteWindowHours: z.number().int().min(1).max(720),
+  altMaxAccountsPerInvite: z.number().int().min(1).max(50)
 });
 export type VerificationConfigDashboard = z.infer<typeof VerificationConfigDashboardSchema>;

--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -186,6 +186,8 @@ const de: Dictionary = {
  'verification.error.account_too_young': 'Dein Account ist zu jung für die Verifizierung.',
  'verification.error.missing_permissions': 'Dem Bot fehlen Berechtigungen.',
  'verification.error.invalid_role': 'Die Verifizierungsrolle ist ungültig.',
+  'verification.error.alt_detected':
+    'Verifizierung abgelehnt: möglicher Zweitaccount erkannt.',
  'verification.error.generic': 'Verifizierung fehlgeschlagen.',
  'verification.captcha.success': 'Captcha bestanden. Du wurdest verifiziert.',
  'verification.captcha.invalid': 'Captcha ungültig oder abgelaufen.',
@@ -769,6 +771,8 @@ const en: Dictionary = {
  'verification.error.account_too_young': 'Your account is too young to verify.',
  'verification.error.missing_permissions': 'Bot lacks permissions.',
  'verification.error.invalid_role': 'Verification role is invalid.',
+  'verification.error.alt_detected':
+    'Verification denied: possible alternate account detected.',
  'verification.error.generic': 'Verification failed.',
  'verification.captcha.success': 'Captcha passed. You have been verified.',
  'verification.captcha.invalid': 'Captcha invalid or expired.',
--- a/packages/shared/src/phase2.ts
+++ b/packages/shared/src/phase2.ts
@@ -207,13 +207,28 @@ export type VerificationMode = z.infer<typeof VerificationModeSchema>;
 export const VerificationFailActionSchema = z.enum(['KICK', 'BAN', 'NONE']);
 export type VerificationFailAction = z.infer<typeof VerificationFailActionSchema>;

+export const CaptchaProviderSchema = z.enum([
+  'MATH',
+  'RECAPTCHA_V2',
+  'RECAPTCHA_V3',
+  'HCAPTCHA',
+  'TURNSTILE'
+]);
+export type CaptchaProvider = z.infer<typeof CaptchaProviderSchema>;
+
 export const VerificationSetupSchema = z.object({
  channel: z.string().min(1),
  verifiedRole: z.string().min(1),
  unverifiedRole: z.string().optional(),
  mode: VerificationModeSchema.default('BUTTON'),
+  captchaProvider: CaptchaProviderSchema.default('MATH'),
  minAccountAgeDays: z.number().int().nonnegative().default(0),
-  failAction: VerificationFailActionSchema.default('KICK')
+  failAction: VerificationFailActionSchema.default('KICK'),
+  altDetectionEnabled: z.boolean().default(false),
+  altBlockOnMatch: z.boolean().default(true),
+  altIpWindowDays: z.number().int().min(1).max(365).default(30),
+  altInviteWindowHours: z.number().int().min(1).max(720).default(48),
+  altMaxAccountsPerInvite: z.number().int().min(1).max(50).default(3)
 });
 export type VerificationSetup = z.infer<typeof VerificationSetupSchema>;