source: http://www.securityfocus.com/bid/38250/info

The MS Comment component for Joomla! is prone to a security-bypass vulnerability because it fails to properly sanitize user-supplied input. The component is also prone to a security-bypass vulnerability because it fails to reset the CAPTCHA after a submission.

An attacker may leverage these issues to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may help the attacker steal cookie-based authentication credentials and launch other attacks.

MS Comment 0.8.0b is vulnerable; other versions may also be affected. 

The following example commands are available:

" onmouseover="alert(String.fromCharCode(88,83,83))

" style="color:expression(alert(String.fromCharCode(88,83,83))) 