phpMyFAQ before 4.1.2 contains an improper restriction of excessive authentication attempts vulnerability in the /admin/check endpoint, which accepts arbitrary user-id parameters without session binding or rate limiting. Unauthenticated attackers can brute-force any user's six-digit TOTP code by submitting POST requests with sequential token values, bypassing two-factor authentication to gain full administrative access.

Affected: Packagist: thorsten/phpmyfaq, Packagist: phpmyfaq/phpmyfaq

## Summary

The `/admin/check` endpoint in `AuthenticationController` implements `SkipsAuthenticationCheck`, making it reachable without any prior authentication. An anonymous attacker (Bob) can POST arbitrary `user-id` and `token` values to brute-force any user's 6-digit TOTP code. No rate limiting exists. The 10^6 keyspace is exhaustible in minutes. Reachability confirmed against a default install: unauthenticated `POST /admin/check` with a `user-id` body field returns HTTP 302 to `/admin/token?user-id=<value>`, echoing the attacker-supplied user id without any binding to a prior password-phase authentication.

## Details

**File**: `phpmyfaq/src/phpMyFAQ/Controller/Administration/AuthenticationController.php`, lines 35-36 and 201-228.

The controller class declaration:

```php final class AuthenticationController extends AbstractAdministrationController implements SkipsAuthenticationCheck ```

The `SkipsAuthenticationCheck` interface (`phpmyfaq/src/phpMyFAQ/Controller/Administration/SkipsAuthenticationCheck.php`) is a marker interface that tells the `ControllerContainerListener` to skip authentication enforcement. Every route in this controller is reachable without a session.

The `check` action (line 201-228):

```php #[Route(path: '/check', name: 'admin.auth.check', methods: ['POST'])] public function check(Request $request): RedirectResponse { if ($this->currentUser->isLoggedIn()) { return new RedirectResponse(url: './'); }

$token = Filter::filterV…