components/com_user/models/reset.php in Joomla! 1.5 through 1.5.5 does not properly validate reset tokens, which allows remote attackers to reset the "first enabled user (lowest id)" password, typically for the administrator.
https://www.exploit-db.com/exploits/6234
https://exchange.xforce.ibmcloud.com/vulnerabilities/44430
http://www.securitytracker.com/id?1020687
http://www.securityfocus.com/bid/30667
http://securityreason.com/securityalert/4157
http://secunia.com/advisories/31457
http://developer.joomla.org/security/news/241-20080801-core-password-remind-functionality.html