The Booktics – Booking Calendar for Appointments and Service Businesses plugin for WordPress is vulnerable to unauthorized modification of data in all versions up to, and including, 1.0.23. This is due to the create_order_permission() permission callback on the POST /wp-json/booktics/v1/orders REST route unconditionally returning true, combined with find_and_update_guest() overwriting an existing customer record's stored name, phone, and wp_user_id whenever the caller-supplied email matches, with no proof of ownership. This makes it possible for unauthenticated attackers to overwrite the contact details (name and phone) of any existing customer whose email address they know, poisoning downstream reminder emails, SMS, calendar invites, and CRM data.