mailnews.cgi 1.3 and earlier allows remote attackers to execute arbitrary commands via a user name that contains shell metacharacters.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-0271
http://www.securityfocus.com/bid/2391
http://archives.neohapsis.com/archives/bugtraq/2001-02/0347.html