The Security component in Apple OS X before 10.10.2 does not properly process cached information about app certificates, which allows attackers to bypass the Gatekeeper protection mechanism by leveraging access to a revoked Developer ID certificate for signing a crafted app.
https://exchange.xforce.ibmcloud.com/vulnerabilities/100525
http://www.securitytracker.com/id/1031650
http://support.apple.com/HT204244
http://lists.apple.com/archives/security-announce/2015/Jan/msg00003.html