The BA Book Everything plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'booking_service_qty' parameter in all versions up to, and including, 1.8.28 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. Successful exploitation requires that an administrator or other privileged user opens the injected order record in the plugin's wp-admin order management area, which is the plugin's ordinary order-review workflow.