A Denial of Service (DoS) vulnerability in Fortinet FortiOS 5.4.0 to 5.4.5 allows an authenticated user to cause the web GUI to be temporarily unresponsive, via passing a specially crafted payload to the 'params' parameter of the JSON web API.
https://fortiguard.com/psirt/FG-IR-17-206
http://www.securitytracker.com/id/1039678
http://www.securityfocus.com/bid/101559
http://code610.blogspot.com/2017/10/patch-your-fortinet-cve-2017-14182.html