DotNetNuke before 4.8.2, during installation or upgrade, does not warn the administrator when the default (1) ValidationKey and (2) DecryptionKey values cannot be modified in the web.config file, which allows remote attackers to bypass intended access restrictions by using the default keys.
https://exchange.xforce.ibmcloud.com/vulnerabilities/41399
http://www.securityfocus.com/archive/1/489957/100/0/threaded
http://www.dotnetnuke.com/News/SecurityBulletins/SecurityBulletinno12/tabid/1148/Default.aspx