Port 23 (Telnet)
Unencrypted remote terminal access, still found on routers, IoT devices and legacy systems.
- Transport
- TCP
- Internet exposure
- Never expose
Should not be reachable from the internet.
Security notes
- Everything, including passwords, is sent in cleartext.
- The Mirai botnet spread in 2016 by logging in to IoT devices over Telnet with default passwords.
- Replace with SSH wherever the device supports it.
When it shows up in your logs
Inbound Telnet attempts are almost always automated botnet scanning for default credentials.
Related ports
- 22 SSH
- 2323