Cross-site request forgery (CSRF) vulnerability in global.php in MyBB before 1.6.5 allows remote attackers to hijack the authentication of a user for requests that change the user's language via the language parameter.
https://exchange.xforce.ibmcloud.com/vulnerabilities/71462
http://www.securityfocus.com/bid/50816
http://secunia.com/advisories/46951
http://dev.mybb.com/issues/1729
http://blog.mybb.com/2011/11/25/mybb-1-6-5-released-feature-update-security-maintenance-release/