The CentralNotice extension for MediaWiki before 1.19.9, 1.20.x before 1.20.8, and 1.21.x before 1.21.3 sets the Cache-Control header to cache session cookies when a user is autocreated, which allows remote attackers to authenticate as the created user.
https://bugzilla.wikimedia.org/show_bug.cgi?id=53032
http://lists.wikimedia.org/pipermail/mediawiki-announce/2013-November/000135.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-December/123011.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-December/122998.html