WFTPD and WFTPD Pro 2.41 allows remote attackers to cause a denial of service by executing an MLST command before logging into the server.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2000-0643
http://www.securityfocus.com/bid/1506
http://archives.neohapsis.com/archives/bugtraq/2000-07/0295.html