WordPress before 3.7.5, 3.8.x before 3.8.5, 3.9.x before 3.9.3, and 4.x before 4.0.1 might allow remote attackers to obtain access to an account idle since 2008 by leveraging an improper PHP dynamic type comparison for an MD5 hash.
https://wordpress.org/news/2014/11/wordpress-4-0-1/
http://www.securitytracker.com/id/1031243
http://www.mandriva.com/security/advisories?name=MDVSA-2014:233
http://www.debian.org/security/2014/dsa-3085