The Rox Appointment Booking – Appointment Booking Scheduling Solution plugin for WordPress is vulnerable to Privilege Escalation via Mass Assignment in all versions up to, and including, 1.3.1 This is due to the public `/rox-appointment-booking/v1/public/booking` REST endpoint performing mass-assignment of the raw request body into a new customer row while `CustomerModel::$fillable` includes the internal `wp_user_id` column, allowing an unauthenticated attacker to persist an arbitrary WordPress user ID alongside an attacker-controlled email address with no authorization check. When an administrator subsequently opens the poisoned customer record and clicks Update Customer, `SaveCustomer::handleRequest()` passes the stored `wp_user_id` and attacker-supplied email to `wp_update_user()` — succeeding because `LinkedAccount::canChange()` unconditionally returns true when the acting user holds the `edit_users` capability — thereby overwriting the targeted administrator's email address and enabling full account takeover via a standard WordPress password-reset request. Successful exploitation requires an administrator to open and save the poisoned record, and the attacker must know or guess a valid administrator user ID (such as the default user ID 1).