Summary
phpMyFAQ contains an authentication bypass in its public two-factor authentication verification flow. An unauthenticated attacker may combine an account's numeric user ID with a valid or guessed six-digit TOTP code to take over a 2FA-enabled account, including an administrator account, without knowing its password.
Affected context
The vulnerability affects phpMyFAQ deployments where the public TOTP verification endpoint accepts an account identifier and verifies a code without confirming that the requester previously completed password authentication. It is especially risky for installations with 2FA-enabled administrative or other privileged accounts and insufficient controls on repeated verification attempts.
Exploit preconditions
- Attack surface: Public two-factor authentication verification flow
- Required access: No prior authentication; the attacker needs an account's numeric user ID
- Trigger point: Submission of a six-digit TOTP value to the verification endpoint
- Why exploitation is possible: TOTP verification is not bound to a session created after successful password authentication, and unrestricted or weakly controlled attempts may permit code guessing
Why this happens
The underlying flaw is an authentication-state validation error. The application treats successful possession or guessing of a second-factor code as sufficient for account authentication without first establishing that the password factor was successfully verified in the same authenticated flow. This maps to CWE-287: Improper Authentication, because the application fails to correctly enforce the required identity-verification sequence and trust relationship.
Potential impact
- An attacker may take over any affected 2FA-enabled account
- An attacker could gain administrative access to phpMyFAQ
- An attacker may read, alter, or delete FAQ content and application data
- An attacker could change account settings or use compromised privileges to affect other users
General mitigation guidance
Mitigation generally focuses on enforcing the intended multi-factor authentication sequence and reducing opportunities for code guessing.
Common defensive patterns include:
- Require successful password authentication before beginning TOTP verification
- Bind the TOTP challenge to the authenticated session, account, and intended authentication transaction
- Apply strict rate limits, attempt counters, and temporary lockouts to failed TOTP submissions
- Avoid exposing account identifiers or authentication state beyond what the flow requires
- Apply least privilege to administrative accounts and review existing sessions after suspected compromise
- Use secure session rotation and invalidation when authentication factors are completed or fail
How teams detect issues like this
Organizations can assess this weakness through:
- Static and dynamic tests that verify TOTP endpoints reject requests without a preceding authenticated password session
- Code review checks for second-factor verification that accepts user IDs independently of server-side authentication state
- Testing for missing rate limits, lockouts, session binding, and authentication-state transitions
- Monitoring for repeated TOTP failures, unusual account-ID enumeration, and successful 2FA events without corresponding password-authentication events
- Policy enforcement requiring multi-factor authentication flows to maintain a server-side, transaction-bound authentication context
