CVE-2026-13424: Online Scheduling and Appointment Booking System <= 27.7 - Unauthenticated Stored Cross-Site Scripting via bookly_speed_up_update_addons AJAX action

The Online Scheduling and Appointment Booking System – Bookly plugin for WordPress is vulnerable to Stored Cross-Site Scripting via booklyspeedupupdateaddons AJAX action in all versions up to, and including, 27.7 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The injection point is the booklyspeedupupdateaddons AJAX action, which is registered as wpajaxnopriv and therefore reachable without authentication; the payload is stored verbatim in the booklylog.details column when a request is submitted without a valid signature, and executes when an administrator later views the Diagnostics → Logs page.