The Online Scheduling and Appointment Booking System – Bookly plugin for WordPress is vulnerable to time-based SQL Injection via the 'staff_ids' parameter in all versions up to, and including, 27.5 due to insufficient escaping on the user supplied parameter and lack of sufficient preparation on the existing SQL query. This makes it possible for unauthenticated attackers to append additional SQL queries into already existing queries that can be used to extract sensitive information from the database. Exploitation requires a two-request chain: an attacker first calls the unauthenticated bookly_get_form_id action to seed a booking session carrying malicious staff_ids values, then triggers bookly_render_time to cause the tainted array to reach the vulnerable query; CSRF/nonce validation is absent on both endpoints, meaning this chain can be initiated cross-site.