Bypass firewalls using ssh

Ever wanted to access a service behind a firewall that has port 22 open for ssh connections? This is a common setup known as using a jump-box for security access and to be successful at this we your firewall must allow port 22 traffic to your ssh jump-box. We can test our if port 22 is open by typing the following line.

telnet ssh-jump-box 22

If all is good then we should see something like
Connected to ssh-jump-box.
Escape character is '^]'.
SSH-2.0-OpenSSH_4.7p1 Debian-8ubuntu1.2

In this example we’re going to create a tunnel for port 3389 windows rdekstop and we’ll begin by creating a local loopback port 3390 that ssh will tunnel from myMachine to myFireWalledMachine on port 3389

ssh -L 3390:server-behindFirewall:3389 user@ssh-jumpbox -N

Now we can access the service on port 3389 that was previously inaccessible through the firewall by pointing our connection to the local loopback port we just created through ssh. In this case we\’ll use rdesktop to hit that port as we are trying to remote desktop to a firewalled machine.

rdesktop localhost:3390

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