Opera before 10.63 does not prevent interpretation of a cross-origin document as a CSS stylesheet when the document lacks a CSS token sequence, which allows remote attackers to obtain sensitive information via a crafted document.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12208
http://www.opera.com/support/kb/view/971/
http://www.opera.com/docs/changelogs/windows/1063/
http://www.opera.com/docs/changelogs/unix/1063/
http://www.opera.com/docs/changelogs/mac/1063/