Port 23 — Telnet
Quick reference for TCP/UDP port 23, used by Telnet. Includes what the service does, security guidance and related ports.
What is port 23?
Plain-text remote login. Insecure — disable on production routers.
What port does Telnet use?
Telnet listens on port 23 by default.
Is port 23 open? How to check
Run one of these from your computer, replacing HOST with the IP address or domain you want to test.
nc -zv HOST 23
Test-NetConnection HOST -Port 23
nmap -p 23 HOST
A refused or timed-out connection means the port is closed or filtered by a firewall.
Security guidance
High risk — do not expose to the internet
Port 23 (Telnet) is high-risk because the service it carries is a frequent target for credential attacks, brute force or unpatched-vulnerability scanning. Keep it bound to localhost or your VPN, never forward it directly on a router, and require strong authentication.
Devices that use port 23
12 devices in our database expose a service on port 23.
Related ports
Frequently asked
What is port 23 used for?+
Port 23 is the standard TCP/UDP port for Telnet. Plain-text remote login. Insecure — disable on production routers.
What port does Telnet use?+
Telnet listens on port 23 by default.
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