Port 23: Telnet
Unencrypted remote terminal.
- Port
- 23
- Protocol
- TCP
- Service
- Telnet
- Exposure
- Do not expose to the internet
What is port 23 used for?
Old network gear and embedded devices.
Is it safe to expose port 23 to the internet?
Everything, including passwords, crosses the network in clear text. Turn it off and use SSH.
If port 23 seems closed or unreachable
- Check that the Telnet service is running and listening on port 23, not only on 127.0.0.1.
- Check the firewall on the host itself (Windows Defender Firewall, iptables, nftables, ufw) for a rule that allows TCP 23.
- If the host is behind a router, confirm the forwarding rule points to the correct internal address and that your internet provider does not use carrier-grade NAT.
- Test from outside your own network. A port can be open locally and blocked at the edge, or the other way round.
Using port 23 safely
Treat port 23 as an internal-only service. Reach it through a VPN or an SSH tunnel, restrict it by source address, and keep the software that listens on it patched.
Check whether port 23 is open on your host
The check connects from our server, so it shows what the internet can reach.
Open the port checker