PORT 23 / TCPSecurity & RemoteExposure Risk: Critical

Port 23: Telnet — Unencrypted Text Communications

Legacy remote terminal protocol that transmits all traffic including passwords in plaintext. Should be disabled in favor of SSH (Port 22).

Default Service

Telnet

Process: telnetd

Transport Protocol

TCP

IANA Registered Port 23

Docker Port Flag

-p 23:23

Container to Host Mapping

How to Check & Kill Process on Port 23 (EADDRINUSE Fix)

macOS & Linux (lsof / kill)

# Find process using port 23
sudo lsof -i :23

# Instantly kill process on port 23
lsof -ti:23 | xargs kill -9

Windows (PowerShell & CMD)

# Find PID listening on port 23
netstat -ano | findstr :23

# Force kill by PID
taskkill /PID <PID_NUMBER> /F

Cross-Platform Node.js One-Liner

# Kill port 23 via npx
npx kill-port 23

# Or diagnose via Castov CLI
npx castov fix "EADDRINUSE :::23"

Linux Firewall (UFW) & Connectivity Test

# Test if port 23 is reachable
nc -zv localhost 23

# Allow or deny port 23 in UFW
sudo ufw allow 23/tcp

Frequently Asked Questions about Port 23

What is Port 23 used for?

Port 23 is the standard network port for Telnet (Unencrypted Text Communications) operating over TCP. The typical system daemon or process is telnetd.

How do I kill a process running on Port 23 (EADDRINUSE)?

On macOS and Linux, run: lsof -ti:23 | xargs kill -9 (or npx kill-port 23). On Windows PowerShell/CMD, run: netstat -ano | findstr :23 and then taskkill /PID <PID> /F.

Is it safe to expose Port 23 to the internet?

Port 23 has a Critical security risk profile. Legacy remote terminal protocol that transmits all traffic including passwords in plaintext. Should be disabled in favor of SSH (Port 22).