Network Port: 23
Network Port Reference Guide
Registered Service Name
Telnet
Transport Protocol
TCP
Functional Overview
Port 23 is used by Telnet, an obsolete protocol for bidirectional text-based terminal communications.
Security Risks & Vulnerabilities
Critical threat. All commands, passwords, and sessions are transmitted in cleartext. Should be permanently disabled in favor of SSH (Port 22).
How to audit network port status
1. Scan Open Ports: Use our Port Scanner utility to verify if this port is actively listening on your host.
2. Verify Encryption: Audit the service layer to confirm SSL/TLS is protecting transmission payload.
3. Hardening Rules: Apply the firewall instructions below to shut down unauthorized inbound ports.
UFW Firewall Rules
Allow Command
sudo ufw allow 23/tcp
Block Command
sudo ufw deny 23/tcp
iptables Firewall Rules
Allow Command
sudo iptables -A INPUT -p tcp --dport 23 -j ACCEPT
Block Command
sudo iptables -A INPUT -p tcp --dport 23 -j DROP