include/controlcenter/users.php in Phorum before 5.1.22 allows remote authenticated moderators to gain privileges via a modified (1) user_ids POST parameter or (2) userdata array.
http://www.vupen.com/english/advisories/2007/1479
http://www.securitytracker.com/id?1017936
http://www.securityfocus.com/archive/1/466286/100/0/threaded
http://www.phorum.org/story.php?76
http://securityreason.com/securityalert/2617