Carl has successfully compromised a web server from behind a firewall by exploiting a
vulnerability in the web server program. He wants to proceed by installing a backdoor program.
However, he is aware that not all inbound ports on the firewall are in the open state.
From the list given below, identify the port that is most likely to be open and allowed to reach the
server that Carl has just compromised.

A.
53

B.
110

C.
25

D.
69

Explanation:
Port 53 is used by DNS and is almost always open,the problem is often that the port
is opened for the hole world and not only for outside DNS servers.