Race condition in Login Window in Apple Mac OS X 10.6.x before 10.6.2, when at least one account has a blank password, allows attackers to bypass password authentication and obtain login access to an arbitrary account via unspecified vectors.
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