The LatePoint - Appointment Booking & Reservation plugin for WordPress is vulnerable to Insecure Direct Object Reference in versions up to, and including, 5.6.9. This is due to the process_step_customer() function using is_user_logged_in() as the sole gate before merging POSTed customer data into an existing LatePoint customer, without any ownership checks. This makes it possible for authenticated attackers, with Subscriber-level access and above, to modify the personal information (first name, last name, email, phone, notes) of arbitrary LatePoint customers, and, when the contact_merge setting is 'phone', to overwrite the victim's email address and take over the account via a password reset.