SecurityAgent in Apple OS X before 10.10 does not ensure that a Kerberos ticket is in the cache for the correct user, which allows local users to gain privileges in opportunistic circumstances by leveraging a Fast User Switching login.
https://support.apple.com/kb/HT6535
https://exchange.xforce.ibmcloud.com/vulnerabilities/97623
http://www.securitytracker.com/id/1031063
http://archives.neohapsis.com/archives/bugtraq/2014-10/0101.html