authentik deactivated service accounts can authenticate to OAuth

@@ -126,6 +126,30 @@ def test_no_provider(self):
             },
         )
 
+    def test_deactivate(self):
+        """test deactivated user"""
+        self.user.is_active = False
+        self.user.save()
+        response = self.client.post(
+            reverse("authentik_providers_oauth2:token"),
+            {
+                "grant_type": GRANT_TYPE_CLIENT_CREDENTIALS,
+                "scope": SCOPE_OPENID,
+                "client_id": self.provider.client_id,
+                "username": "sa",
+                "password": self.token.key,
+            },
+        )
+        self.assertEqual(response.status_code, 400)
+        self.assertJSONEqual(
+            response.content.decode(),
+            {
+                "error": "invalid_grant",
+                "error_description": TokenError.errors["invalid_grant"],
+                "request_id": response.headers["X-authentik-id"],
+            },
+        )
+
     def test_permission_denied(self):
         """test permission denied"""
         group = Group.objects.create(name="foo")

@@ -336,7 +336,7 @@ def __post_init_client_credentials_creds(
         self, request: HttpRequest, username: str, password: str
     ):
         # Authenticate user based on credentials
-        user = User.objects.filter(username=username).first()
+        user = User.objects.filter(username=username, is_active=True).first()
         if not user:
             raise TokenError("invalid_grant")
         token: Token = Token.filter_not_expired(

@@ -0,0 +1,25 @@
+# CVE-2025-64521
+
+## Deactivated service account can authenticate to OAuth
+
+### Summary
+
+When authenticating with `client_id` and `client_secret` to an OAuth provider, authentik creates a service account for the provider. In previous authentik versions, authentication for this account was possible even when the account was deactivated. Other permissions are correctly applied and federation with other providers still take assigned policies correctly into account.
+
+### Patches
+
+authentik 2025.8.5 and 2025.10.2 fix this issue, for other versions the workaround below can be used.
+
+### Workarounds
+
+You can add a policy to your application that explicitly checks if the service account is still valid, and deny access if not.
+
+```python
+return request.user.is_active
+```
+
+### For more information
+
+If you have any questions or comments about this advisory:
+
+- Email us at [security@goauthentik.io](mailto:security@goauthentik.io).