Revive Adserver before 3.2.5 and 4.0.0 suffers from Special Element Injection. Usernames weren't properly sanitised when creating users on a Revive Adserver instance. Especially, control characters were not filtered, allowing apparently identical usernames to co-exist in the system, due to the fact that such characters are normally ignored when an HTML page is displayed in a browser. The issue could have therefore been exploited for user spoofing, although elevated privileges are required to create users within Revive Adserver.