The current_url parameter of the AJAX call to the GalleryBox action of admin-ajax.php is vulnerable to reflected Cross Site Scripting. The value of the current_url parameter is embedded within an existing JavaScript within the response allowing arbitrary JavaScript to be inserted and executed. No authentication is required to exploit this issue. Note that other parameters within a AJAX call, such as image_id, must be valid for this vulnerability to be successfully exploited.
Vulmon