The Login Window component in Apple OS X before 10.11 does not ensure that the screen is locked at the intended time, which allows physically proximate attackers to obtain access by visiting an unattended workstation.
https://support.apple.com/HT205267
http://www.securitytracker.com/id/1033703
http://www.securityfocus.com/bid/76908
http://lists.apple.com/archives/security-announce/2015/Sep/msg00008.html