Default configuration in Matt Wright FormHandler.cgi script allows arbitrary directories to be used for attachments, and only restricts access to the /etc/ directory, which allows remote attackers to read arbitrary files via the reply_message_attach attachment parameter.
Directory traversal vulnerability in Matt Wright FormHandler.cgi script allows remote attackers to read arbitrary files via (1) a .. (dot dot) in the reply_message_attach attachment parameter, or (2) by specifying the filename as a template.
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 "-->".