Opera before 12.13 does not send CORS preflight requests in all required cases, which allows remote attackers to bypass a CSRF protection mechanism via a crafted web site that triggers a CORS request.
http://www.opera.com/support/kb/view/1045/
http://www.opera.com/docs/changelogs/unified/1213/
http://lists.opensuse.org/opensuse-updates/2013-02/msg00038.html