The password generation in mailman before 2.1.5 generates only 5 million unique passwords, which makes it easier for remote attackers to guess passwords via a brute force attack.
https://exchange.xforce.ibmcloud.com/vulnerabilities/18857
http://www.novell.com/linux/security/advisories/2005_07_mailman.html
http://secunia.com/advisories/13603/