The Cascading Style Sheets (CSS) implementation in WebKit in Apple Safari before 5.0 on Mac OS X 10.5 through 10.6 and Windows, and before 4.1 on Mac OS X 10.4, does not properly handle the :visited pseudo-class, which allows remote attackers to obtain sensitive information about visited web pages via a crafted HTML document.
http://www.vupen.com/english/advisories/2011/0552
http://www.vupen.com/english/advisories/2011/0212
http://www.vupen.com/english/advisories/2010/2722
http://www.vupen.com/english/advisories/2010/1373
http://www.ubuntu.com/usn/USN-1006-1
http://www.securityfocus.com/bid/40756
http://www.securityfocus.com/bid/40620
http://www.mandriva.com/security/advisories?name=MDVSA-2011:039
http://support.apple.com/kb/HT4196
http://securitytracker.com/id?1024067
http://secunia.com/advisories/43068
http://secunia.com/advisories/41856
http://secunia.com/advisories/40105
http://lists.opensuse.org/opensuse-security-announce/2011-01/msg00006.html
http://lists.apple.com/archives/security-announce/2010/Jun/msg00000.html