Adaptive Firewall in Apple Mac OS X before 10.6.2 does not properly handle invalid usernames in SSH login attempts, which makes it easier for remote attackers to obtain login access via a brute-force attack (aka dictionary attack).
http://www.vupen.com/english/advisories/2009/3184
http://www.securityfocus.com/bid/36956
http://support.apple.com/kb/HT3937
http://lists.apple.com/archives/security-announce/2009/Nov/msg00000.html