The wp_validate_auth_cookie function in wp-includes/pluggable.php in WordPress before 3.7.2 and 3.8.x before 3.8.2 does not properly determine the validity of authentication cookies, which makes it easier for remote attackers to obtain access via a forged cookie.
https://bugzilla.redhat.com/show_bug.cgi?id=1085858
http://www.debian.org/security/2014/dsa-2901
http://core.trac.wordpress.org/changeset/28054