Grav before 2.0.4 contains a two-factor authentication bypass vulnerability in the login plugin where the regenerate2FASecret task checks only user existence, not authorization, during the pending TOTP challenge window. Attackers who know the victim's password can call this task without a CSRF nonce to overwrite the 2FA secret with an attacker-chosen value, compute a valid TOTP code, and complete authentication while reducing 2FA to password-only protection.