Related Posts for WordPress < 2.0.4 - Authenticated Reflected Cross-Site Scripting (XSS)

Unvalidated input and lack of output encoding within the Related Posts for WordPress plugin before 2.0.4 lead to a Reflected Cross-Site Scripting (XSS) vulnerability within the 'lang' GET parameter while editing a post, triggered when users with the capability of editing posts access a malicious URL.