Appointment Booking Plugin <= 5.7.4 - Unauthenticated Authentication Bypass via Race Condition on OTP Attempts Counter

The Appointment Booking Plugin – LatePoint | Calendar & Scheduling for WordPress plugin for WordPress is vulnerable to Authentication Bypass via Race Condition in all versions up to, and including, 5.7.4. This is due to a non-atomic read-modify-write on the OTP verification attempts counter in the verifyOTP function: the counter is incremented using a stale in-memory value with no conditional WHERE attempts < 10 guard on the UPDATE and no SELECT ... FOR UPDATE row lock, creating a TOCTOU window that allows concurrent requests to bypass the 10-attempt lockout. This makes it possible for unauthenticated attackers — who know a target customer's registered email address or phone number — to fire concurrent requests to the auth__verify_otp endpoint, defeat the lockout cap, brute-force the 6-digit OTP code, and authenticate as the targeted LatePoint customer, gaining full access to their account, bookings, and personal data. The nonce check present on the endpoint (otp_verify_otp_nonce) does not mitigate this issue, as the nonce is publicly emitted by the unauthenticated request_otp and resend_otp endpoints and is trivially obtainable by any unauthenticated attacker prior to launching the race.