The ApiBase::getWatchlistUser function in MediaWiki before 1.23.10, 1.24.x before 1.24.3, and 1.25.x before 1.25.2 does not perform token comparison in constant time, which allows remote attackers to guess the watchlist token and bypass CSRF protection via a timing attack.
https://security.gentoo.org/glsa/201510-05
https://lists.wikimedia.org/pipermail/mediawiki-announce/2015-August/000179.html
https://euvd.enisa.europa.eu/vulnerability/EUVD-2015-6666
http://www.securityfocus.com/bid/76334
http://www.openwall.com/lists/oss-security/2015/08/27/6
http://www.openwall.com/lists/oss-security/2015/08/12/6
http://lists.fedoraproject.org/pipermail/package-announce/2015-August/165193.html