phpMyFAQ is an open source FAQ web application. Prior to version 4.0.18, the WebAuthn prepare endpoint (`/api/webauthn/prepare`) creates new active user accounts without any authentication, CSRF protection, captcha, or configuration checks. This allows unauthenticated attackers to create unlimited user accounts even when registration is disabled. Version 4.0.18 fixes the issue.

Affected: Packagist: thorsten/phpmyfaq

### Summary

The WebAuthn prepare endpoint (`/api/webauthn/prepare`) creates new active user accounts without any authentication, CSRF protection, CAPTCHA, or configuration checks. This allows unauthenticated attackers to create unlimited user accounts even when registration is disabled.

### Details

**File:** `phpmyfaq/src/phpMyFAQ/Controller/Frontend/Api/WebAuthnController.php`, lines 63-79

```php #[Route(path: 'webauthn/prepare', name: 'api.private.webauthn.prepare', methods: ['POST'])] public function prepare(Request $request): JsonResponse { $data = json_decode($request->getContent(), ...); $username = Filter::filterVar($data->username, FILTER_SANITIZE_SPECIAL_CHARS);

if (!$this->user->getUserByLogin($username, raiseError: false)) { try { $this->user->createUser($username); $this->user->setStatus(status: 'active'); $this->user->setAuthSource(AuthenticationSourceType::AUTH_WEB_AUTHN->value); $this->user->setUserData([ 'display_name' => $username, 'email' => $username, ]); ```

The endpoint: 1. Accepts any POST request with a JSON `username` field 2. If the username doesn't exist, creates a new **active** user account 3. Does NOT check if WebAuthn support is enabled (`security.enableWebAuthnSupport`) 4. Does NOT check if registration is enabled (`security.enableRegistration`) 5. Does NOT verify CSRF tokens 6. Does NOT require captcha validation 7. Has no rate…