CVE-2006-4403
The FTP server in Apple Mac OS X 10.4.8 and earlier, when FTP Access is enabled, will crash when a login failure occurs with a valid user name, which allows remote attackers to cause a denial of service (crash) and enumerate valid usernames.
Date published : 2006-11-30
http://lists.apple.com/archives/security-announce/2006/Nov/msg00001.html