diff --git a/docker-compose.yml b/docker-compose.yml
index b641dee..beaea4b 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -23,6 +23,8 @@ services:
       - OLLAMA_MODEL=${OLLAMA_MODEL:-llava}
       - SCANNER_ARCHIVE_DIR=${SCANNER_ARCHIVE_DIR:-/data/scanner/_processed_archive}
       - OIDC_ISSUER=${OIDC_ISSUER:-}
+      # Audience-Prüfung der Tokens – muss dieselbe Client-ID wie im Frontend sein
+      - OIDC_CLIENT_ID=${OIDC_CLIENT_ID:-${VITE_OIDC_CLIENT_ID:-ogOeIlrcsf2spjuwyOc7CuAPrRkRSt3RXfYguoLn}}
       - SMTP_HOST=${SMTP_HOST:-}
       - SMTP_PORT=${SMTP_PORT:-587}
       - SMTP_SECURE=${SMTP_SECURE:-false}
diff --git a/paperless-backend/src/auth/jwt-optionen.spec.ts b/paperless-backend/src/auth/jwt-optionen.spec.ts
new file mode 100644
index 0000000..9ea57d2
--- /dev/null
+++ b/paperless-backend/src/auth/jwt-optionen.spec.ts
@@ -0,0 +1,46 @@
+import { generateKeyPairSync } from 'crypto';
+import * as jwt from 'jsonwebtoken';
+import { jwtPruefOptionen } from './jwt-optionen';
+
+describe('jwtPruefOptionen', () => {
+  it('verlangt die eigene Client-ID als Audience, wenn sie gesetzt ist', () => {
+    expect(
+      jwtPruefOptionen('https://auth.example/application/o/pm/', 'client-pm'),
+    ).toEqual({
+      issuer: 'https://auth.example/application/o/pm/',
+      audience: 'client-pm',
+      algorithms: ['RS256'],
+      jwksUri: 'https://auth.example/application/o/pm/jwks/',
+    });
+  });
+
+  it('lässt die Audience weg, wenn keine Client-ID konfiguriert ist', () => {
+    const o = jwtPruefOptionen('https://auth.example/application/o/pm', '');
+    expect(o.audience).toBeUndefined();
+    expect(o.jwksUri).toBe('https://auth.example/application/o/pm/jwks/');
+  });
+
+  // Prüft, dass die Optionen in jsonwebtoken (das passport-jwt intern nutzt)
+  // tatsächlich fremde Tokens desselben Issuers abweisen.
+  it('weist Tokens anderer Anwendungen desselben Authentik ab', () => {
+    const { privateKey, publicKey } = generateKeyPairSync('rsa', {
+      modulusLength: 2048,
+    });
+    const o = jwtPruefOptionen('https://auth.example/', 'client-pm');
+    const token = (aud: string) =>
+      jwt.sign({ sub: 'u1' }, privateKey, {
+        algorithm: 'RS256',
+        issuer: o.issuer,
+        audience: aud,
+      });
+    const pruefe = (t: string) =>
+      jwt.verify(t, publicKey, {
+        issuer: o.issuer,
+        audience: o.audience,
+        algorithms: o.algorithms,
+      });
+
+    expect(() => pruefe(token('client-pm'))).not.toThrow();
+    expect(() => pruefe(token('client-andere-app'))).toThrow(/audience/);
+  });
+});
diff --git a/paperless-backend/src/auth/jwt-optionen.ts b/paperless-backend/src/auth/jwt-optionen.ts
new file mode 100644
index 0000000..55c2034
--- /dev/null
+++ b/paperless-backend/src/auth/jwt-optionen.ts
@@ -0,0 +1,27 @@
+import type { Algorithm } from 'jsonwebtoken';
+
+export interface JwtPruefOptionen {
+  issuer: string;
+  /** Client-ID dieser Anwendung; ohne sie wird `aud` nicht geprüft. */
+  audience?: string;
+  algorithms: Algorithm[];
+  jwksUri: string;
+}
+
+/**
+ * Prüfoptionen für Access-Tokens von Authentik. Ohne Audience-Prüfung würde
+ * jedes Token desselben Issuers akzeptiert – also auch eines, das Authentik
+ * für eine andere Anwendung mit demselben Provider ausgestellt hat.
+ */
+export function jwtPruefOptionen(
+  issuer: string,
+  clientId: string | undefined,
+): JwtPruefOptionen {
+  const basis = issuer.endsWith('/') ? issuer.slice(0, -1) : issuer;
+  return {
+    issuer,
+    ...(clientId ? { audience: clientId } : {}),
+    algorithms: ['RS256'],
+    jwksUri: `${basis}/jwks/`,
+  };
+}
diff --git a/paperless-backend/src/auth/jwt.strategy.ts b/paperless-backend/src/auth/jwt.strategy.ts
index 5c47830..4dc0ee4 100644
--- a/paperless-backend/src/auth/jwt.strategy.ts
+++ b/paperless-backend/src/auth/jwt.strategy.ts
@@ -1,9 +1,10 @@
-import { Injectable } from '@nestjs/common';
+import { Injectable, Logger } from '@nestjs/common';
 import { PassportStrategy } from '@nestjs/passport';
 import { Strategy, ExtractJwt } from 'passport-jwt';
 import { ConfigService } from '@nestjs/config';
 import { passportJwtSecret } from 'jwks-rsa';
 import { mapGroupsToPermissions } from './permissions.enum';
+import { jwtPruefOptionen } from './jwt-optionen';
 import { UserIdentitySyncService } from '../user-settings/user-identity-sync.service';
 
 @Injectable()
@@ -12,20 +13,31 @@ export class JwtStrategy extends PassportStrategy(Strategy, 'jwt') {
     configService: ConfigService,
     private readonly identitySync: UserIdentitySyncService,
   ) {
-    const issuer = configService.get<string>('OIDC_ISSUER', '');
+    const optionen = jwtPruefOptionen(
+      configService.get<string>('OIDC_ISSUER', ''),
+      configService.get<string>('OIDC_CLIENT_ID', ''),
+    );
 
     super({
       jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
       ignoreExpiration: false,
-      issuer,
-      algorithms: ['RS256'],
+      issuer: optionen.issuer,
+      audience: optionen.audience,
+      algorithms: optionen.algorithms,
       secretOrKeyProvider: passportJwtSecret({
         cache: true,
         rateLimit: true,
         jwksRequestsPerMinute: 5,
-        jwksUri: `${issuer.endsWith('/') ? issuer.slice(0, -1) : issuer}/jwks/`,
+        jwksUri: optionen.jwksUri,
       }),
     });
+
+    if (!optionen.audience) {
+      new Logger(JwtStrategy.name).warn(
+        'OIDC_CLIENT_ID ist nicht gesetzt – die Audience von Tokens wird NICHT geprüft. ' +
+          'Tokens anderer Anwendungen desselben Authentik würden akzeptiert.',
+      );
+    }
   }
 
   validate(payload: any): {