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TCP
Vulnerable
23 Telnet
Telnet provides remote terminal access without transport encryption, which is why modern systems usually disable it.
Security Context
Port 23 is high-risk when broadly exposed. Treat it as an attack-surface decision, not just a connectivity setting, and confirm whether the listener truly needs to be reachable.
- !Telnet credentials and session data travel in cleartext.
Nmap Check
Use a version probe first so you confirm whether the expected service is really what is listening on this port.
nmap -sV -p 23 <host>Firewall Commands
UFW
sudo ufw allow 23/tcpiptables
sudo iptables -A INPUT -p tcp --dport 23 -j ACCEPT