Opera before 10.01 does not properly restrict HTML in a (1) RSS or (2) Atom feed, which allows remote attackers to conduct cross-site scripting (XSS) attacks, and conduct cross-zone scripting attacks involving the Feed Subscription Page to read feeds or create feed subscriptions, via a crafted feed, related to the rendering of the application/rss+xml content type as "scripted content."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A6314
https://exchange.xforce.ibmcloud.com/vulnerabilities/54021
http://www.vupen.com/english/advisories/2009/3073
http://www.securityfocus.com/bid/36850
http://www.securityfocus.com/bid/36418
http://www.securityfocus.com/archive/1/506517/100/0/threaded
http://www.opera.com/support/kb/view/939/
http://www.opera.com/docs/changelogs/windows/1001/
http://www.opera.com/docs/changelogs/unix/1001/
http://www.opera.com/docs/changelogs/mac/1001/
http://securethoughts.com/2009/10/hijacking-operas-native-page-using-malicious-rss-payloads/
http://secunia.com/advisories/37182
http://archives.neohapsis.com/archives/bugtraq/2009-10/0289.html