XSS vulnerability in ArtGK CMS forum

Vulnerability ID: HTB22587
Reference: http://www.htbridge.ch/advisory/xss_vulnerability_in_artgk_cms.html
Product: ArtGK CMS
Vendor: ArtGK ( http://artgk-cms.ru/ )
Vulnerable Version: 2009-08-28 16:00:00 and Probably Prior Versions
Vendor Notification: 18 August 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 "/cms/classes/CForm.php" script to properly sanitize user-supplied input in "content" 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. For this purposes go to the forum thread, enter exploit code like 'XSS"><script>alert(document.cookie)</script>' to the forum reply message textarea, fill captcha and click on the "Send" button.