includes/User.php in MediaWiki before 1.16.5, when wgBlockDisablesLogin is enabled, does not clear certain cached data after verification of an auth token fails, which allows remote attackers to bypass authentication by creating crafted wikiUserID and wikiUserName cookies, or by leveraging an unattended workstation.
lists.fedoraproject.org/pipermail/package-announce/2011-May/060435.html
lists.fedoraproject.org/pipermail/package-announce/2011-May/060496.html
lists.fedoraproject.org/pipermail/package-announce/2011-May/060507.html
lists.wikimedia.org/pipermail/mediawiki-announce/2011-May/000098.html
secunia.com/advisories/44684
www.securityfocus.com/bid/47722
bugzilla.redhat.com/show_bug.cgi?id=702512
bugzilla.wikimedia.org/show_bug.cgi?id=28639