WebKit in Apple Safari before 6.0 does not properly handle Cascading Style Sheets (CSS) property values, which allows remote attackers to bypass the Same Origin Policy via a crafted web site.
http://support.apple.com/kb/HT5503
http://support.apple.com/kb/HT5400
http://lists.apple.com/archives/security-announce/2012/Sep/msg00003.html
http://lists.apple.com/archives/security-announce/2012/Jul/msg00000.html