Cannot access FortiGate Web GUI (web admin interface)

If the certificate on your LAN (SSH enabled) port is expired or failed to renew, the web interface simply stops working. The solution is to set the admin server certificate to use the FortiGate Factory certificate.

SSH into FortiGate and then issue the following command:

config system global

set admin-server-cert Fortinet_Factory

end

NOTE: To be sure this is your actual problem, you can turn debug on and check

diagnose debug application httpds -1
diagnose debug enable

Expect to see output from debug which looks like below when attempting to access the web interface
Can’t open certificate file …