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CVE-2026-56737 – Two-Factor Authentication Bypass – phpMyFAQ 3.2.0–4.1.5

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Summary

CVE-2026-56737 is an authentication bypass vulnerability (CWE-287: Improper Authentication) in phpMyFAQ’s public two-factor authentication (2FA) verification flow. It affects phpMyFAQ versions 3.2.0 through 4.1.5 and carries a CVSS v3.1 base score of 8.1 (High), as the flaw allows an unauthenticated attacker to fully take over any 2FA-enabled account, including administrator accounts, without ever supplying the account password.

Technical details

  • The public 2FA verification endpoint (POST /check in AuthenticationController.php) accepts login based solely on an attacker-supplied numeric user ID and a valid six-digit TOTP token.
  • No server-side check confirms the requesting party has already passed password authentication before this endpoint is reached.
  • The code loads the user record from the supplied ID, validates only the TOTP code, and then calls the session-establishing success routine — effectively treating TOTP as a single, standalone authentication factor.
  • By contrast, the admin login flow correctly enforces a password-first requirement via a pending-authentication session flag; the public-facing flow omits this check.
  • Because there is no rate limiting on the endpoint, an attacker can brute-force the six-digit TOTP code for a known or guessed user ID.
  • Attack vector is network-based, requires no user interaction and no privileges, but does require additional attack complexity (guessing/brute-forcing the TOTP code) since the password is not needed.
  • Successful exploitation results in full account takeover — confidentiality, integrity, and availability are all impacted at the highest level, since compromise of an administrator account grants full control of the FAQ installation.

Affected software

  • phpMyFAQ versions 3.2.0 through 4.1.5 (inclusive), where the account has 2FA enabled.

Severity

  • CVSS v3.1 Base Score: 8.1 (High)
  • Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade phpMyFAQ to version 4.1.6 or later, which binds TOTP verification to a session established only after successful password authentication and adds rate-limiting on failed TOTP attempts.
  • If patching is not immediately possible: Restrict or disable the public 2FA login endpoint at the network/WAF layer, monitor for repeated TOTP submission attempts against the same or sequential user IDs, and consider temporarily disabling 2FA-based login until the upgrade can be applied, since 2FA in the vulnerable versions does not add the intended security benefit.

References

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