An FBX-5313 issue was discovered in WatchGuard Fireware before 12.0. When a failed login attempt is made to the login endpoint of the XML-RPC interface, if JavaScript code, properly encoded to be consumed by XML parsers, is embedded as value of the user element, the code will be rendered in the context of any logged in user in the Web UI visiting "Traffic Monitor" sections "Events" and "All." As a side effect, no further events will be visible in the Traffic Monitor until the device is restarted.