The Keychain implementation in Apple Mac OS X 10.6.8 and earlier does not properly handle an untrusted attribute of a Certification Authority certificate, which makes it easier for man-in-the-middle attackers to spoof arbitrary SSL servers via an Extended Validation certificate, as demonstrated by https access with Safari.
https://exchange.xforce.ibmcloud.com/vulnerabilities/69556
http://www.securitytracker.com/id?1026002
http://www.securityfocus.com/bid/49429
http://support.apple.com/kb/HT5130
http://lists.apple.com/archives/security-announce/2012/Feb/msg00000.html