ad.cgi CGI program by Leif Wright allows remote attackers to execute arbitrary commands via shell metacharacters in the file parameter.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5741
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-0025
http://www.securityfocus.com/bid/2103
http://archives.neohapsis.com/archives/bugtraq/2000-12/0143.html