The Accounts Preferences implementation in Apple Mac OS X 10.6 before 10.6.3, when a network account server is used, does not support Login Window access control that is based solely on group membership, which allows attackers to bypass intended access restrictions by entering login credentials.
http://www.securityfocus.com/bid/39153
http://support.apple.com/kb/HT4077
http://lists.apple.com/archives/security-announce/2010//Mar/msg00001.html