CFNetwork in Safari in Apple Mac OS X before 10.5.3 automatically sends an SSL client certificate in response to a web server's certificate request, which allows remote web sites to obtain sensitive information (Subject data) from personally identifiable certificates, and use arbitrary certificates to track user activities across domains, a related issue to CVE-2007-4879.

More... (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-1580)