[Lordzy]

The server will automatically set player as RCON administrator upon logging in using /rcon login. The best way to resolve this would be to use the actual rcon command as second rcon. Anyone who logs in as rcon administrator without being passed by server sided rcon login can be kicked. Another way would, if I'm recalling correctly, YSF provided a function to set as RCON administrator using it's function. You can use it to disable the player being RCON administrator on the first login and grant access only if they've passed the second RCON login.