How do I check if port 23 is open?

Enter your public IP or hostname into the scanner tool and click Check. A sub-second raw TCP socket handshake will be initiated from our edge server to port 23 on your target. If the 3-way handshake finishes with SYN-ACK, the port is OPEN. If an RST packet is returned, the host is reachable but the port is CLOSED. If packets time out without response, the port is FILTERED by an ISP or firewall.

Is port 23 safe to expose to the public internet?

Exposing port 23 carries elevated security risks (Critical risk). Obsolete and dangerously insecure. Passwords and commands are sent in clear text across the internet. Replace with SSH immediately. For remote services, consider placing them behind a secure VPN (such as WireGuard or Tailscale) or restricting inbound access with strict IP firewall rules.

Why does port 23 show as closed or filtered?

If port 23 reports CLOSED or FILTERED, confirm that: 1) Your service is actively running and bound to 0.0.0.0 (not just localhost/127.0.0.1); 2) Your router has a port forwarding rule directing external port 23 to your machine's local IP; 3) Your operating system firewall (Windows Defender Firewall, ufw, or iptables) allows incoming connections on port 23.

PORT 23 TCP Remote Access Critical Risk

Port 23 (Telnet (Unencrypted Remote Terminal)) Open Check

Q: What is port 23 used for?

Port 23 is the standard TCP port used for Telnet (Unencrypted Remote Terminal). It is commonly used by Telnet Daemon, Legacy Router Consoles, Industrial IoT Devices. Legacy command-line terminal protocol transmitting all credentials and keystrokes in plaintext.

Legacy command-line terminal protocol transmitting all credentials and keystrokes in plaintext.

Live Socket Reachability Probe

Pre-configured for Port 23

Port Scanner

Quick:

Recent Probes 0

Stored locally in browser • 0 logs on server

No recent scans recorded.

Target hosts and tested ports will appear here automatically for fast 1-click re-testing.

Auto-prunes oldest probes beyond 10 entries (FIFO)

Port Specifications & Network Behavior

Standard Port Number 23

Primary Service Telnet (Unencrypted Remote Terminal)

Transport Protocol TCP

Traffic Classification Remote Access

Residential ISP Status Typically unrestricted by consumer ISPs

Security Exposure Critical Exposure discouraged without VPN or firewall protection

Security Advisory: Telnet (Unencrypted Remote Terminal) (Port 23)

Obsolete and dangerously insecure. Passwords and commands are sent in clear text across the internet. Replace with SSH immediately.

Recommendation: Keep port 23 closed to WAN traffic. Connect remotely using WireGuard, Tailscale, or an SSH tunnel.

Port Forwarding & Troubleshooting Checklist

If port 23 returns CLOSED or FILTERED, work through this verified diagnostic checklist:

1 Verify if telnetd service is active on host.
2 Check router forwarding table.
3 Strong recommendation: Disable Telnet and switch to OpenSSH (port 22).

Verify Host Is Listening Locally

Windows (PowerShell) netstat -ano | findstr :23

Linux / macOS (Bash) ss -tulpn | grep :23

Associated Software & Frameworks

Telnet Daemon Legacy Router Consoles Industrial IoT Devices

Related Remote Access Ports

Frequently co-hosted services and alternate protocol ports

Standard encrypted protocol for command-line access, remote system administration, and SFTP transfers.

Remote Access Check

:3389 TCP

Critical

Remote Desktop Protocol (RDP)

Microsoft proprietary protocol providing graphic remote desktop management for Windows hosts.