(1) ApiBlock.php, (2) ApiCreateAccount.php, (3) ApiLogin.php, (4) ApiMain.php, (5) ApiQueryDeletedrevs.php, (6) ApiTokens.php, and (7) ApiUnblock.php in includes/api/ in MediaWiki 1.19.x before 1.19.8, 1.20.x before 1.20.7, and 1.21.x before 1.21.2 allow remote attackers to obtain CSRF tokens and bypass the cross-site request forgery (CSRF) protection mechanism via a JSONP request to wiki/api.php.
https://www.mediawiki.org/wiki/Release_notes/1.21
https://www.mediawiki.org/wiki/Release_notes/1.20
https://www.mediawiki.org/wiki/Release_notes/1.19
https://exchange.xforce.ibmcloud.com/vulnerabilities/86896
https://bugzilla.wikimedia.org/show_bug.cgi?id=49090
http://www.debian.org/security/2013/dsa-2753
http://secunia.com/advisories/54715
http://seclists.org/oss-sec/2013/q3/553
http://lists.wikimedia.org/pipermail/mediawiki-announce/2013-September/000133.html