HTB22997: XSS in A Really Simple Chat (ARSC)

Vulnerability ID: HTB22997
Reference: http://www.htbridge.ch/advisory/xss_in_a_really_simple_chat_arsc.html
Product: A Really Simple Chat (ARSC)
Vendor: http://www.reallysimplechat.org/ ( http://www.reallysimplechat.org/ )
Vulnerable Version: 3.3-rc2
Vendor Notification: 12 May 2011
Vulnerability Type: XSS (Cross Site Scripting)
Risk level: Medium
Credit: High-Tech Bridge SA Security Research Lab ( http://www.htbridge.ch/advisory/ )

Vulnerability Details:
User can execute arbitrary JavaScript code within the vulnerable application.
The vulnerability exists due to failure in the "dereferer.php" script to properly sanitize user-supplied input in "arsc_link" variable.
Successful exploitation of this vulnerability could result in a compromise of the application, theft of cookie-based auwhentication credentials, disclosure or modification of sensitive data.
The following PoC is available:

http://[host]/base/dereferer.php?arsc_link=%22%3E%3Cscript%3Ealert%28document.cookie%29;%3C/script%3E