check.php in Hinton Design phphg Guestbook 1.2 does not check the user password when authenticating via cookies, which allows remote attackers to gain unauthorized access.
http://www.vupen.com/english/advisories/2006/0480
http://www.securityfocus.com/bid/16541
http://www.securityfocus.com/archive/1/424740/100/0/threaded
http://securitytracker.com/id?1015620