source: http://www.securityfocus.com/bid/25085/info

The WP-FeedStats plugin for WordPress is prone to an HTML-injection vulnerability because it fails to sufficiently sanitize user-supplied input data.

Exploiting this issue may allow an attacker to execute HTML and script code in the context of the affected site, to steal cookie-based authentication credentials, or to control how the site is rendered to the user; other attacks are also possible.

This issue affects versions prior to WP-FeedStats 2.4. 

http://www.example.com/_wp1/?feed=rss2&<script>alert(1)</script>