Port 23 · Telnet

Port 23 is Telnet, TCP.

Unencrypted terminal protocol. Cleartext credentials. Deprecated — replace with SSH.

Palo Alto

Create the service object for this port, then allow the App-ID on it. Restricting the rule to the port's service object keeps the rule working on a non-default port and stops the App-ID matching on other ports. Replace the placeholders with your own rule name and zones.

set service tcp-23 protocol tcp port 23

set rulebase security rules <rule-name> from <from-zone> to <to-zone> source any destination any application telnet service tcp-23 action allow

Risk and exposure

Rated high risk. Services on this port are commonly targeted by attackers. Keep it off the internet, or put it behind a VPN or a strict source allow-list, and monitor access.

Check it

• Linux ss -tlnp | grep :23
• PowerShell Test-NetConnection <host> -Port 23
• nmap nmap -p 23 <host>

Related ports

• 1723 PPTP
• 20 FTP Data
• 21 FTP Control
• 22 SSH
• 5900 VNC
• 5985 WinRM HTTP

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