Greetings!
Here is a sure stop:
/ip firewall filter add chain=input src-address=xx.xx.xx.xx/24 action=accept
/ip firewall filter add chain=input action=drop
The second line must be the last entry in your input filter list.
Insure they are entered in that order.
xx.xx.xx.xx/24 is your wan net.
And you still get access to everything! But beware! If you don't have a null modem cable handy, this could lock you out if not entered correctly.
NOTE: Here is the way I lock myself out of my boxes most often. If you don't like the way the rules are working and want to delete them, REMOVE THAT SECOND LINE FIRST!! Otherwise, the only input rule is the second one, which is "everybody is locked out". When the response from the box suddenly stops, you'll know what I mean.