libsecurity in Apple Mac OS X before 10.7.4 does not properly restrict the length of RSA keys within X.509 certificates, which makes it easier for remote attackers to defeat cryptographic protection mechanisms by conducting a spoofing or network-sniffing attack during communication with a site that uses a short key.
http://www.securityfocus.com/bid/53462
http://www.securityfocus.com/bid/53445
http://support.apple.com/kb/HT5281
http://lists.apple.com/archives/security-announce/2012/May/msg00001.html