This is a tool to overcome the deep packet inspection that is used against secure shell protocol. Deep packet inspection is a broad concept that involves use of several techniques with the same idea in common. It consists in deeply analyzing the network packets and applying rules and/or data mining over these same techniques. The use of deep packet inspection is morally questionable and poses a fundamental problem to the transparent use of Internet services. This is a simple tool that aims to avoid the filtering of SSH packets over a network that is being actively monitoring and droping this kind of packets.
Typically there are two different ways of blocking the use of a service in the network. The first consists in dropping all tcp packets from all the ports but a few. With this kind of blocking a simple telnet host port would end up in a refused or not allowed connection. The second one is a little more sneaky and does allow you to connect any port, or at least don't explicitly blocks you, instead it keeps analyzing the patterns inside the packets and when some pattern that is blacklisted like ssh or smtp handshake messages then it will drop following packets for that TCP connection. The fundamental difference is the first don't allow you even to establish a tcp connection while the second simply start dropping the following packets after the pattern is found and matched with an internal blacklist. So if you can connect to a host:port and suddently the traffic just stops to flow that is a strong indicator that your network is being actively monitored. If you wanna be sure about that you can simply change the protocol over that port if, for instance, you have control over the server that is hosting the service in that port. As an example you can just change ssh port with the HTTP port and retry the connections. What most certainly will happen is that the strange behavior has now swapped ports this kind of dynamic blocking is only possible because the packets are being deeply monitored and changed/drop depending in a set of rules defined by whom controls the network topology.
First you got to clone the project into your working space
git clone git@github.com:Balhau/gossh2http.git
The next step we need to do is configure the GOROOT environment path
export GOPATH=$HOME/<working_folder>/gossh2http
After you need to checkout some dependencies
go get github.com/fatih/color
go get github.com/urfave/cli
Then you need to go into the src folder and type
go build ssh2http.go
To check the command line documentation you can run
./ssh2http help
and get an output like the following. Note that this is yet in development and more changes are to come
NAME:
ssh2http - Ssh to http packet wrapping
USAGE:
ssh2http --from <local_ssh2http_ip>:<port --to <remote_ssh2http_tunnel>:<port>
VERSION:
1.0.0
AUTHOR:
Balhau <balhau@balhau.net>
COMMANDS:
help, h Shows a list of commands or help for one command
GLOBAL OPTIONS:
--from value, -f value source HOST:PORT (default: "127.0.0.1:10000") [$SSH_FROM]
--to value, -t value destination HOST:PORT [$SSH_TO]
--serve, -s list local addresses
--help, -h show help
--version, -v print the version
COPYRIGHT:
MIT License
To use this program you need to start the executable in two different points.
The idea behind this is explained in the following diagram
|------------| |---------------| wrappedPackets |---------------| |---------|
| sshClient | -->| wrapperClient | --------------->| wrapperServer | --->|sshServer|
|------------| |---------------| |---------------| |---------|
So for this you need to start the wrapperServer in a machine outside the monitored network, and a wrapperClient in your sshClient machine, the steps are the following
sudo ./ssh2http -s -f localhost:10000 -t sshserver.com:22 --> In the server machine
./ssh2http -f localhost:10000 -t sshserver.com:10000
ssh login@localhost:10000
As an running example you can check here for a demo
This tool was inspired in a very nice tool developed from a friend. FWD Thanks @kintoandar for that