The Appointment Bookings for Zoom GoogleMeet and more - Wappointment plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to and including 2.7.6 via the appointmentkey parameter due to the appointment edit_key, the sole authorization token consumed by tryCancel(), being generated as a predictable, unsalted MD5 hash of only client_id (a sequential integer), start_at (a publicly observable appointment timestamp), and staff_id (a small enumerable integer), with no secret salt or random component, and the unauthenticated cancellation and rescheduling REST endpoints performing no ownership or identity verification beyond matching this reconstructible key. This makes it possible for unauthenticated attackers to compute valid edit_key values for appointments belonging to other users and cancel or reschedule those appointments arbitrarily. Exploitation requires the allow_cancellation or allow_rescheduling setting to be enabled on the site, both of which are common configurations for active booking deployments.

an attacker can obtain the inputs needed to reconstruct a victim's key by booking their own appointment to observe their sequential client_id and correlating publicly visible appointment times and enumerable staff identifiers.