WordPress Event Calendar (Spider Event Calendar) <= 1.5.65 is vulnerable to Reflected Cross-Site Scripting (XSS) vulnerability

The SpiderCalendar WordPress plugin through 1.5.65 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.