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.

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CWE: CWE-287