Setting up unsecure telnet

Question

I want to demonstrate serial communications in a class. Is it possible/how to set up a good old port 23 unencrypted console service in Ubuntu?

score 0 · Answer 1 · answered Aug 17 '21 at 06:55

You can install and start a telnet server with this small process. For your information, telnet default port is not 22 (ssh) but 23.

sudo apt install inetutils-telnetd telnet

Edit the file /etc/inetd.conf and comment out the following line

telnet  stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/telnetd

Then restart inet server.

sudo systemctl restart inetutils-inetd

To snif packages, use then tcpdump. You can install with the following command.

sudo apt install tcpdump

Use the following command to display the traffic on port 23 (keep the terminal open, and open a new one).

sudo tcpdump -A -i lo dst port 23

Finally, run telnet on your computer.

telnet localhost 23

Login with your local account, you will see the written text in clear into tcpdump.

1 Answers1