The User::randomPassword function in MediaWiki before 1.23.12, 1.24.x before 1.24.5, 1.25.x before 1.25.4, and 1.26.x before 1.26.1 generates passwords smaller than $wgMinimalPasswordLength, which makes it easier for remote attackers to obtain access via a brute-force attack.
https://phabricator.wikimedia.org/T115522
https://lists.wikimedia.org/pipermail/mediawiki-announce/2015-December/000186.html