Port 23 (TCP) — Telnet

Unencrypted remote terminal.

🔒 Runs locally — your input never leaves this browser tab

Never expose. Common entry point for IoT botnets.

Check if port 23 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':23 '

From another machine, test reachability:

nc -zv your-server.example.com 23

With UFW (Ubuntu/Debian):

sudo ufw deny 23

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=23/tcp && sudo firewall-cmd --reload