CFNetwork in Apple Mac OS X before 10.7.2 does not properly follow an intended cookie-storage policy, which makes it easier for remote web servers to track users via a cookie, related to a "synchronization issue."
http://www.securityfocus.com/bid/50085
http://support.apple.com/kb/HT5002
http://lists.apple.com/archives/Security-announce/2011//Oct/msg00003.html