Apple Safari allows remote attackers to discover a redirect's target URL, for the session of a specific user of a web site, by placing the site's URL in the HREF attribute of a stylesheet LINK element, and then reading the document.styleSheets[0].href property value.
http://www.vupen.com/english/advisories/2011/0552
http://www.vupen.com/english/advisories/2010/2722
http://www.ubuntu.com/usn/USN-1006-1
http://www.mandriva.com/security/advisories?name=MDVSA-2011:039