The best protection against the abuse of remote maintenance of PBX (Private Branch Exchange) system is to:
A.
Keep maintenance features turned off until needed
B.
Insists on strong authentication before allowing remote maintenance
C.
Keep PBX (Private Branch Exchange) in locked enclosure and restrict access to only a few people.
D.
Check to see if the maintenance caller is on the list of approved maintenance personnel
Explanation:
Checking with various outside opinions, answer A would be the best.
Answer A.
Keeping the remote maintenance features turned off until needed prevents abuse from this vector – as an intruder cannot access the service while off – and the only times you are at risk are when the features are turned on.