Network ports · 23
23 — Telnet
Port 23 is the legacy Telnet service, which sends everything including passwords in clear text.
Key facts
| Port | 23 |
|---|---|
| Transport | TCP |
| Service | Telnet |
| Encryption | None |
| Status | Obsolete for remote administration |
| Range | Well-known (0–1023) |
No encryption at all
Telnet provides a remote terminal with no confidentiality or integrity. Every keystroke, including the login and password, crosses the network in clear text. On any shared or untrusted path, that is equivalent to publishing the credentials.
It is still found on old network equipment, printers and embedded devices. Those devices are exactly the ones that tend to have weak default passwords, which makes port 23 a common target for botnets.
What to use instead
Use SSH for remote shells and disable Telnet on every device that allows it. If a legacy device only speaks Telnet, place it on an isolated management network and reach it through a jump host, never directly from the internet.
An open port 23 on a public address is usually a sign of an unmanaged device. Scan for it, identify the owner, and close it.
Frequently asked questions
Is Telnet still used?
Mostly for testing text protocols and for legacy embedded devices. It is not appropriate for remote administration.
Can I tunnel Telnet over SSH?
Yes. That protects the traffic, but the device still needs to be trusted and isolated.