vBulletin 5.x through 5.5.4 allows remote command execution via the widgetConfig[code] parameter in an ajax/render/widgetphp routestring request.
The install/upgrade.php scripts in vBulletin 4.1 and 5 allow remote attackers to create administrative accounts via the customerid, htmldata[password], htmldata[confirmpassword], and htmldata[email] parameters, as exploited in the wild in October 2013.