Lars Ellingsen guestserver.cgi allows remote attackers to execute arbitrary commands via shell metacharacters in the "email" parameter.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6027
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-0180
http://archives.neohapsis.com/archives/bugtraq/2001-01/0471.html