The Bookly plugin for WordPress is vulnerable to Insecure Direct Object Reference in versions up to, and including, 27.7 via the appointment() method of the Mobile Staff Cabinet API (resource=appointment, action=bookly_mobile_staff_cabinet) in frontend/modules/mobile_staff_cabinet/api/handlers/Handler1_0.php. This is due to the handler loading an Appointment by the attacker-supplied params[id] without verifying that the appointment's staff_id matches the authenticated staff member, whereas sibling operations (deleteAppointment, saveAppointment, appointments list) correctly scope to $this->staff->getId() when $this->role === ROLE_STAFF. This makes it possible for authenticated attackers, with staff-level mobile cabinet access (any valid access_key token bound to a Staff entity), to read appointment details — including the internal note and the full customer_appointments collection (customer full_name, email, phone, notes, custom_fields, extras, payment_total, payment_type, payment_status) — belonging to other staff members by enumerating sequential appointment IDs.