PGPMail.pl 1.31 allows remote attackers to execute arbitrary commands via shell metacharacters in the (1) recipient or (2) pgpuserid parameters.
FormMail.pl in FormMail 1.6 and earlier allows a remote attacker to send anonymous email (spam) by modifying the recipient and message parameters.
guestbook.pl cleanses user-inserted SSI commands by removing text between "<!--" and "-->" separators, which allows remote attackers to execute arbitrary commands when guestbook.pl is run on Apache 1.3.9 and possibly other versions, since Apache allows other closing sequences besides "-->".
WWWBoard has a default username and default password.
FormMail CGI program allows remote execution of commands.