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September 10, 2022 02:58 pm GMT

Setting up a simple SOCKS proxy tunnel over SSH

If you have any kind of Linux/Unix server accessible over SSH, it's very easy to use it as a simple proxy server. This can be useful to bypass content filters and other restrictions on your local Internet connection. Even the cheapest Linux/BSD VPS options will be more than enough for this.

This feature is built into OpenSSH, and you don't need to install any additional software, or do any additional configuration.

All you need to do is open an ssh connection from the client side with a dynamic port forwarding option:

ssh -D 1080 myserver

-D option tells ssh to use the local 1080 port for dynamic, application-level port forwarding. In a practical sense, this means that your ssh client will act as a SOCKS 4/5 server on that port.

Depending on your configuration, you may also need to specify an SSH port and user (i.e. ssh -p 2222 myuser@myserver, but in that case, you may want to consider setting up a host profile in your ~/.ssh/config file instead).

After that, all you need to do is tell your browser to use a SOCKS proxy on localhost:1080.

Browser setup

In Firefox, you can set SOCKS proxy in Settings / Network Settings / Configure Proxy Access to the Internet - Manual proxy configuration:

SOCKS Host: localhost
Port: 1080
SOCKS v5

With Google Chrome/Chromium, you need to start the browser with --proxy-server argument:

chromium --proxy-server="socks5://localhost:1080"

Non-interactive / scripting use

If you don't want the SSH client to open an interactive session, you can prevent it from executing the shell with -N flag, and -f flag to put it into the background, i.e.:

ssh -N -f -D 1080 myserver

If you want to automatically restart the connection when necessary, you can use autossh tool (the syntax is the same):

autossh -N -f -D 1080 myserver

Putty

If you're using Putty instead of CLI ssh client, you need to add 1080 as a source port and select Dynamic as a forwarding option under Connection / SSH / Tunnels.

Relevant parts of ssh man page

     -D [bind_address:]port             Specifies a local dynamic application-level port forwarding.             This works by allocating a socket to listen to port on the local             side, optionally bound to the specified bind_address.  Whenever a             connection is made to this port, the connection is forwarded over             the secure channel, and the application protocol is then used to             determine where to connect to from the remote machine.  Currently             the SOCKS4 and SOCKS5 protocols are supported, and ssh will act             as a SOCKS server.  Only root can forward privileged ports.  Dy             namic port forwardings can also be specified in the configuration             file.             IPv6 addresses can be specified by enclosing the address in             square brackets.  Only the superuser can forward privileged             ports.  By default, the local port is bound in accordance with             the GatewayPorts setting.  However, an explicit bind_address may             be used to bind the connection to a specific address.  The             bind_address of localhost indicates that the listening port be             bound for local use only, while an empty address or * indicates             that the port should be available from all interfaces.     -N      Do not execute a remote command.  This is useful for just for             warding ports.     -f      Requests ssh to go to background just before command execution.             This is useful if ssh is going to ask for passwords or             passphrases, but the user wants it in the background.  This im             plies -n.  The recommended way to start X11 programs at a remote             site is with something like ssh -f host xterm.             If the ExitOnForwardFailure configuration option is set to yes,             then a client started with -f will wait for all remote port for             wards to be successfully established before placing itself in the             background.

Note: This is a snapshot of the wiki page from the BetterWays.dev wiki, you can find the latest (better formatted) version here: betterways.dev/setting-up-a-simple-socks-proxy-tunnel-over-ssh.

Original Link: https://dev.to/betterways/setting-up-a-simple-socks-proxy-tunnel-over-ssh-224

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