MediaWiki before 1.18.5, and 1.19.x before 1.19.2 saves passwords in the local database, (1) which could make it easier for context-dependent attackers to obtain cleartext passwords via a brute-force attack or, (2) when an authentication plugin returns a false in the strict function, could allow remote attackers to use old passwords for non-existing accounts in an external authentication system via unspecified vectors.
https://phabricator.wikimedia.org/T41184
https://lists.wikimedia.org/pipermail/mediawiki-announce/2012-August/000119.html
https://bugzilla.redhat.com/show_bug.cgi?id=853442
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=686330