Chaining WebScarab onto another proxy

This document is intended to explain how to configure WebScarab to chain onto an upstream proxy.

I assume that you are familiar with the basic functionality of WebScarab, and have managed to use it as a proxy to view and intercept some conversations already. If not, I suggest reading the "Getting Started" document first.

Stephen Venter 07:37, 16 March 2007 (EDT)

Overview
In the case where you are browsing via a proxy server on your local network, such as is often the case with corporate networks, you will need to configure WebScarab to chain onto that proxy server if it is to work correctly.

Some people refer to this as "Using WebScarab behind a firewall", since it is the firewall that will be blocking all outgoing browser traffic, other than the traffic which originates via the proxy server. But really it is the proxy server that is the key to getting WebScarab working in this circumstance.

Outline of the setup for this example
To do this you obviously need to know that your proxy server’s IP address (or its hostname that resolves on your LAN) together with the port number that the proxy server listens on. For simplicity sake, let’s assume I have a local LAN with network range 192.168.1.0 /24 (which means it has a netmask of 255.255.255.0)and my proxy server is at IP 192.168.1.10 and it listens on port 8080.

If you are not sure what your proxy server’s IP address is and someone else set up your browser such that it is correctly browsing via the proxy, you may be able to view it within your browser’s configuration settings (where it has been manually configured and is not being automatically picked up by the browser – there are other ways of working it out in that case, but I won’t go into that here).

Since I am using Microsoft Internet Explorer in this example, I see my proxy settings here: Tools -> Internet Options -> Connections -> LAN settings -> Use Proxy Server for your LAN -> Address: 192.168.1.10 Port: 8080

I am running WebScarab locally on my PC, using the standard settings. Thus it will be listening on the standard localhost IP address of 127.0.0.1 on port 8008. Some people like to use the name "localhost", I prefer to use the IP address "127.0.0.1" – but they are interchangeable, so it won’t matter which you use.

Step One: Configuring WebScarab to point at my internal network proxy
Note: The port number "3128" is the default value included with the WebScarab setting for chaining onto another proxy server (Tools -> Proxies). It does not necessarily mean that it is the correct port number you should use for your network. In my example outline above, my local network proxy is configured to listen on a port "8080". So that is the value I have to use in WebScarab in: Tools -> Proxies -> ["Port" box for both the "HTTP Proxy" and "HTTPS Proxy"]

Once I have set that correctly, then WebScarab can make connections out of my network via my local network proxy.

CAUTION!! Make sure that the proxy you specify via Tools -> Proxies does not point back to WebScarab's proxy port, otherwise you will end up creating an infinite loop, since WebScarab will now try to use itself as the upstream proxy and will simply run out of sockets or available memory.

Note: If you are using WebScarab on Windows, and Internet Explorer is correctly accessing the outside network through your designated proxy, you may simply be able to access the WebScarab upstream proxy setting via Tools -> Proxies, and click the "Get IE Settings" button. This only works for the "Installer" version of WebScarab, not the Java WebStart or "selfcontained" versions, since it relies on a native Windows library to read this information.

Step Two: Configuring my web browser to send connections via WebScarab
This step is the usual one to use for getting WebScarab to work whether or not I am setting it to chain onto another internal proxy.

The number "3128" is NOT the correct number to use in IE. Also, the network proxy server IP is not what I want to use here either anymore (unless I am connecting out to the internet directly without WebScarab in-between).

As outlined above, I am running webscarab locally on the same PC as I am browsing from. So in IE, I need to put the value "127.0.0.1" into the "Address" box and "8008" into the "Port" box as follows: Tools -> Internet Options -> Connections -> LAN settings -> Use Proxy Server for your LAN -> Address: 127.0.0.1 Port: 8008

Also, I suggest leaving the box for "Automatically detect settings" un-checked / un-ticked. And same goes for the "Bypass proxy server for local addresses" box. If you are intending to only use WebScarab when making connections to sites outside your local network, it doesn't matter. But if you then try to connect to a website on your local LAN, that setting will result in IE connecting directly to that local web server without proxying via WebScarab. So for safety sake, I suggest keeping that box un-checked too.

Now I have:
 * my web browser forwarding connections via WebScarab, which is listening on 127.0.0.1:8008
 * and WebScarab forwarding connections out of my network via my network proxy on IP 192.168.1.10 and port number 8080 (a.k.a. WebScarab is chaining onto that proxy 192.168.1.10:8080).