source: https://www.securityfocus.com/bid/5507/info

Reportedly, Kerio Mailserver is vulnerable to cross site scripting attacks. The vulnerability is present in Kerio Mailserver's web mail component.

An attacker may exploit this vulnerability by causing a victim user to follow a malicious link. Exploitation may result in the compromise of authentication data, or in script code taking actions as the authenticated user.

*** The vendor has stated that this is not a vulnerability. 

*** Proof of concept has been provided.

http://keriowebmail/<script>alert('THisIsREAL0wned')</script>
http://keriowebmail/passwd<script>alert('VERYVULNERABLE')</script>