The which_access variable for Majordomo 2.0 through 1.94.4, and possibly earlier versions, is set to "open" by default, which allows remote attackers to identify the email addresses of members of mailing lists via a "which" command.
Majordomo 1.94.3 and earlier allows remote attackers to execute arbitrary commands when the advertise or noadvertise directive is used in a configuration file, via shell metacharacters in the Reply-To header.