HTB22819: XSS vulnerability in WebAsyst Shop-Script

Vulnerability ID: HTB22819
Reference: http://www.htbridge.ch/advisory/xss_vulnerability_in_webasyst_shop_script_1.html
Product: WebAsyst Shop-Script
Vendor: WebAsyst, LLC ( http://www.shop-script.ru/ )
Vulnerable Version: Current version 2011.01.23 (shop-script.ru/demo/)
Vendor Notification: 25 January 2011
Vulnerability Type: XSS (Cross Site Scripting)
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 to properly sanitize user-supplied input in "app" 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:
http://host/?app=UG"><script>alert(document.cookie)</script>