After running an Nmap scan on a local area network, a penetration tester notices several older Linux servers have port 23 open Which of the following should the systems administrator do as a secunty…

Moving Telnet to a non-standard port is security through obscurity and does not eliminate the plaintext transmission vulnerability that makes Telnet dangerous.

Telnet has no encryption, meaning any traffic including passwords is visible to anyone with network access or a packet capture tool. Disabling and uninstalling the service eliminates the attack surface completely, which is the only way to prevent exploitation of the plaintext protocol. SSH (port 22) should be used as a secure replacement.

Patching the kernel is good hygiene but does not address the fundamental risk of Telnet transmitting all data unencrypted over the network.

Restricting Telnet via firewall reduces exposure but leaves an unencrypted service running, which remains exploitable from any permitted host that is compromised.