This NextGEN Gallery plugin is prone to a cross-site scripting vulnerability. It is really popular plugin for the WordPress content management system, usually found as a blogging platform. The vulnerability manipulates the mode parameter of the xml/media-rss.php script and it results that unsanitized imput can be crafted into an attack by a malicious user.
Update the plugin.
Also you can yse a browser by the server (for the example, Google Chrome, Mozilla Firefox, Opera, Apple Safari), but not Internet Explorer.
Type XSS (Cross Site Scripting) OWASP Top 10 A3: Cross Site Scripting (XSS)