Multiple Reverse shells using the same public port

Question

I´ve got a Server behind a firewall and the firewall only allows traffic through port 22. This server has both public and private addresses.

I´ve got also about 1K clients that I need to reverse shell to this server, and be able to choose one of them by id when I want that ssh reversed tunnel.

My goal is to make the clients connect to ssh server via port 22, and each one of this connections should be forwarded to localhost on port with the same id. When I connect to the server with my laptop also via ssh, I would then ssh to localhost on the correct id and get the client shell.

Can someone provide me the good path to achieve this behaviour using bash, ssh and linux tools?

Note - I don´t want to use client.py and server.py cause most of my clients are android based and it could easily become a nightmare to install python on all of them.

Answer 1

The problem - it was solved using remote port forwarding:

ssh -R 21:localhost:8888 user@server

In this command the 8888 represents the terminal id. In order for this to work, had to add this line to my ssh conf:

GatewayPorts yes