wp-login.php in WordPress 2.8.3 and earlier allows remote attackers to force a password reset for the first user in the database, possibly the administrator, via a key[] array variable in a resetpass (aka rp) action, which bypasses a check that assumes that $key is not an array.
https://exchange.xforce.ibmcloud.com/vulnerabilities/52382
http://www.securitytracker.com/id?1022707
http://www.securityfocus.com/bid/36014
http://wordpress.org/development/2009/08/2-8-4-security-release/