SShuttle

• It doesn't perform a port forward, and the proxy it creates is nothing like the ones we have already seen.

• Instead it uses an SSH connection to create a tunnelled proxy that acts like a new interface.

• It simulates a VPN, allowing us to route our traffic through the proxy without the use of proxychains (or an equivalent).

• We can just directly connect to devices in the target network as we would normally connect to networked devices. As it creates a tunnel through SSH (the secure shell), anything we send through the tunnel is also encrypted.

Limitations

• sshuttle only works on Linux targets.

• It also requires access to the compromised server via SSH, and Python also needs to be installed on the server.

• That said, with SSH access, it could theoretically be possible to upload a static copy of Python and work with that.

sudo apt install sshuttle

• The base command for connecting to a server with sshuttle is as follows:

sshuttle -r username@address subnet 

• For example, in our fictional 172.16.0.x network with a compromised server at 172.16.0.5, the command may look something like this:

sshuttle -r user@172.16.0.5 172.16.0.0/24

• We would then be asked for the user's password, and the proxy would be established.

• The tool will then just sit passively in the background and forward relevant traffic into the target network.

• Rather than specifying subnets, we could also use the -N option which attempts to determine them automatically based on the compromised server's own routing table:

sshuttle -r username@address -N

• If this has worked, you should see the following line:

c : Connected to server.

• sshuttle doesn't currently seem to have a shorthand for specifying a private key to authenticate to the server with. That said, we can easily bypass this limitation using

--ssh-cmd 

• With the --ssh-cmd switch, we can pick a different command to execute for authentication: say, ssh -i keyfile

Final Command

• So, when using key-based authentication, the final command looks something like this:

sshuttle -r user@address --ssh-cmd "ssh -i KEYFILE" SUBNET

• To use our example from before, the command would be:

sshuttle -r user@172.16.0.5 --ssh-cmd "ssh -i private_key" 172.16.0.0/24

Errors

• Please Note: When using sshuttle, you may encounter an error that looks like this:

client: Connected.
client_loop: send disconnect: Broken pipe
client: fatal: server died with error code 255

• This can occur when the compromised machine you're connecting to is part of the subnet you're attempting to gain access to.

• For instance, if we were connecting to 172.16.0.5 and trying to forward 172.16.0.0/24, then we would be including the compromised server inside the newly forwarded subnet, thus disrupting the connection and causing the tool to die.

• To get around this, we tell sshuttle to exclude the compromised server from the subnet range using the -x switch.

• To use our earlier example:

sshuttle -r user@172.16.0.5 172.16.0.0/24 -x 172.16.0.5