In this article, we will go over how you use
proxychains to proxy our traffic through a socks proxy.
Recently like everyone else, I've been working from home a lot more often. This means to access resources at work I need to use a VPN. However, to access some resources, such as production servers from my local machine, I need to use a SOCKS5 proxy. Without using a SOCKS proxy, I would need to do something shown in the diagram below.
First, I would need to SSH onto an intermediate server (
Server A), which I have connectivity to from my local machine. Then on that intermediate server, I would need to SSH onto the production server. So this intermediate server needs to have connectivity to the
Server B as well. As you can see
Server B is behind a firewall, in this example, the firewall will only allow traffic from
Server A to ingress to
Server B. So we cannot connect directly from
Another reason this setup is sub-optimal I lose all the development tools on my local machine. Say I wanted to use terraform to deploy/upgrade a service running on
Server B server. I need to make sure terraform exists on the intermediate server. Now, this is fine for something simple like terraform which is a single binary file but may get more complicated for other pieces of software, especially if you cannot install extra packages on the intermediate server. Also, there are other advantages in using your local development environment: you have all your shortcuts saved, perhaps you use a different shell zsh, fish vs bash on the server itself. For whatever reason, it may be more convenient to access
Server B directly from our local machine.
warning 🔐 Production Access
Now depending on where you work and how your policies work it may not be possible or a good idea to access
your production servers from your local machine. This is just a simple example of one reason you may want to use a SOCKS proxy. There may be many others, such as accessing your test environment instead of production.
In this section, I will show you how to solve the problem we described above. To solve this problem we will need to use.
A SOCKS (🧦 not this kinda socks) proxy, SOCKS is a layer 5 (on the OSI model, shown below) protocol. The protocol will allow us to proxy to
Server A and this server will then act as almost a middleman between the
Local Machine and
Server B. The SOCKS proxy doesn't interpret any network traffic between the client (
Local Machine) and the
Server B), it merely passes it onto between the two.
tip SOCKS Proxy You can learn more about
SOCKS proxies here. This article goes into much more detail than I do!
So finally let's get onto how we can create a SOCKS proxy. To do this we will create an SSH tunnel.
ssh -D 8123 -f -C -q -N firstname.lastname@example.org
-D 8123: Opens a SOCKS5 proxy on local port
-f: Requests SSH to go to the background itself before executing the command
-C: Compresses data before sending it
-q: Quiet mode doesn't show any output
-N: Doesn't execute remote commands, useful for just port forward (protocol 2+)
:::tip Multiple Proxies
You can create multiple SOCKS proxies by running the SSH command binding to different local ports.
If the command worked, you now have a SOCKS proxy. One common use case of a SOCKS proxy is for internet browsing using very much the same logic described above. Maybe you can access a website at work which is behind a firewall, such as an authentication server's GUI etc. You can read more about using a SOCKS proxy, in your browser here.
The diagram gives us a visual of what we've just done.
Now that we have SOCKS proxy running on our local machine, how can we use it to connect to
Server B and say
use terraform to deploy a new service? Well, that's where
proxychains comes in, or rather more specifically
proxychains-ng. The latter being a version which still gets relatively frequent updates. To install
proxychains on an Ubuntu/Debian based distro you can do something like this:
sudo apt install proxychains-ng vim /etc/proxychains4.conf [ProxyList] # add proxy here ... # meanwile # defaults set to "tor" socks5 127.0.0.1 8123
Edit the configuration file as shown above,
socks5 127.0.0.1 8123. Adjust the port
8123 to whatever port you set above. Now that
proxychains is setup. This is what our setup now looks like:
Server B had an IP address of
10.10.10.11 we could do:
proxychains ssh email@example.com
This would allow us to connect directly using SSH. Or perhaps if you had a web service running on
Server B and wanted to check a
healthcheck endpoint to see if your API was running correctly you might do:
proxychains curl https://10.10.10.11/api/v1/healthcheck
Or if you wanted to use terraform to deploy something on
Server B, you could do something like:
tip Terraform To get terraform to use our SOCKS proxy we need to export the
export HTTP_PROXY=socks5://127.0.0.1:8123 export HTTPS_PROXY=socks5://127.0.0.1:8123 proxychains terraform plan proxychains terraform apply
caution ProxyChains TCP proxychains will only proxy TCP connections from your
Local Machine. However, it can resolve DNS through the proxy as well.
What is essentially going on here is that traffic is being sent from our
Local Machine to
Server A which can connect to
Server B and pass traffic to the server. This in effect makes it seem our
Local Machine can connect directly to
So overall we have something as described in the diagram above!