Port 111/TCP is the default port for the RPC (Remote Procedure Call) portmapper service on Unix systems, which registers and manages RPC services.
Why A is correct:Running rpcinfo -p queries the portmapper to list all registered RPC services, their programs, versions, and associated ports. This is a logical next step during a security audit or penetration test to identify potential vulnerabilities (e.g., NFS or NIS services). CNSP recommends this command for RPC enumeration.
Why other options are incorrect:
B. Telnet to the port to look for a banner:Telnet might connect, but RPC services don’t typically provide a human-readable banner, making this less effective than rpcinfo.
C. Telnet to the port, send "GET / HTTP/1.0" and gather information from the response:Port 111 is not an HTTP service, so an HTTP request is irrelevant and will likely fail.
D. None of the above:Incorrect, as A is a valid and recommended step.
References:CNSP "Unix Service Enumeration" (Section on RPC Services) highlights rpcinfo -p as the standard tool for probing port 111/TCP.
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