SpiderCalendar <= 1.5.65 - Reflected Cross-Site Scripting

The plugin does not sanitise and escape the callback parameter before outputting it back in the page via the window AJAX action (available to both unauthenticated and authenticated users), leading to a Reflected Cross-Site Scripting issue.

Note: Vendor decided to close the plugin and it won't be maintained anymore

https://example.com/wp-admin/admin-ajax.php?action=window&callback=%3C/script%3E%3Cimg/src/onerror=alert(/XSS/);%3E