Avoid WebRTC leak if you use browser + VPN or SSH Tunnel

I have been using a SSH tunnel (Please see this post for the instructions, http://swapoff.blogspot.com/2018/03/how-to-create-ssh-tunnel-and-use-it-for.html) for web browsing via Firefox.

I used it to forward DNS queries well. So I thought I'm pretty much safe until I read about WebRTC feature in web browsers.

WebRTC allows P2P communication for real time communication in web browsers.  WebRTC can be used to get your true IP address via STUN requests with browsers, even when you are using a VPN or SSH tunnel.

You can check whether WebRTC is enabled using several methods, but checking it via a web application is easier than any other methods. e.g.: https://browserleaks.com/webrtc

To disable WebRTC in firefox, set media.peerconnection.enabled to false via about:config

How to create SSH tunnel and use it for web browsing

Command

ssh -D 12345 -C -q -N <username>@<ip or FQDN> -p 23456

Explanation

-D ssh will act as a SOCKS server for the given port
-C Compress data
-q quiet mode. warning and diagnostic messages will be suppressed
-N Do not execute a remote command.  just forwarding ports.
<username>@<ip or FQDN> Connection string to SSH server
-p SSH server port. (if it's usual port 22, you can ignore this parameter)

In addition to above options you can use -f option to push ssh command to background

Executing above command will create a SSH tunnel which supports SOCKS protocol.

How to configure Firefox to use the SSH tunnel 

Go to proxy settings and use localhost as "SOCKS Host" and the port you used for the tunnel as the Port (see the screenshot below)

How to configure Firefox to forward DNS queries to the SSH tunnel

Use "Proxy DNS when using SOCKS v5" in proxy settings or set "network.proxy.socks_remote_dns" to "true" via about:config to get DNS queries resolved via the tunnel. Otherwise the browser will use DNS server configured in your network interface or ISP's DNS servers.

How to disable WebRTC in Firefox

Important: Please read http://swapoff.blogspot.com/2018/08/avoid-webrtc-leak-if-you-use-browser.html for instructions to disable WebRTC.