CFNetwork in Apple Mac OS X 10.6.x before 10.6.5 does not properly validate the domains of cookies, which makes it easier for remote web servers to track users by setting a cookie that is associated with a partial IP address.
http://www.securitytracker.com/id?1024723
http://support.apple.com/kb/HT4435
http://lists.apple.com/archives/security-announce/2010//Nov/msg00000.html