In order to create our own custom proxies, first we need to know how proxies work. When I wanted to write a custom proxy tool (it’s a simple Python script) in Hipchat part3, I had to go back and learn how they work. I did not find such a resource online that looked at proxies from an infosec perspective. Most talked about how to configure caching or forwarding proxies and not much about MitM ones. I have briefly talked about it in the section 2 of the same post named How does a Proxy Work?. In this post I am going to take a deep(er) dive. I actually read some RFCs and they were surprisingly well written.

If you want to skip the intro, go to section 3.

Back in March 2014, Garage4Hackers had a live stream with Gynvael Coldwind. His talk was named "Data, data, data! I can't make bricks without clay" or a few practical notes on reverse-engineering. You can see the recording on youtube.

Here are my notes that I discovered from 2014.

I thought I had found the Windows iptables with Portproxy but I was wrong. But I learned something neat in the process and I am documenting it to access it when I need it.

Portproxy allows you to listen on a certain port on one of your network interfaces (or all interfaces) and redirect all traffic to that interface (on your computer) to another port/IP address.

The to that interface is the limitation that unfortunately kills it. This will be a short post.

I have decided to learn Go (or Golang). I went through the Tour of Go and made some notes. Some of the items/code are directly copy pasted from there. The notes are just a cheatsheet to help me look things up quickly while learning. I will update that page as I learn more.

You can see the notes at https://parsiya.net/go/.

I have talked a lot about this and that but have done nothing in action. Now I will talk about proxying actual applications. I will start with something easy, the FileHippo App Manager. This app was chosen because it can be proxied with Burp, it does not use TLS and it has its own proxy settings (also works with Internet Explorer proxy settings). The requests are pretty simple to understand. I like the FileHippo website because it archives old versions of software. For example I loved the non-bloated Yahoo! Messenger 8.0 when I used it (it’s pretty popular in some places) and used FileHippo to download the old versions.

FileHippo App Manager turned out to be more interesting than I thought and this post turned into some .NET reverse engineering using dnSpy. Here’s what I talk about in this post:

• The app contains the AWS SDK and a fortunately invalid set of AWS Access/Secret keys. Both the SDK and the keys are in dead code.
• Requests have an AccessToken header which is generated client-side. We will discuss how it is generated.
• The application has a “hidden” DEBUG mode which unfortunately does nothing special. We will discover how to enable it.

It’s been a while since Burp part four and I want to continue writing these. It’s time to actually proxy applications. However I have three problems:

1. I was too busy at work.
2. I could not find a lot of interesting applications that are interesting to proxy and can showcase different Burp functionalities that we talked about.
3. I found some interesting applications but there were security vulns so I am going through disclosure (unfortunately I may never be able to release them publicly).

The last point was a surprise, these are decently popular apps and I could not believe that no one has looked at them before.

Nevertheless, I will continue soon.

In the meanwhile, Burp version 1.7 has been released. Now we have Burp projects. Instead of saving the state everyday, we can use one project file that contains all the items. Pretty cool. Some of the items have changed, especially options. Now it has User Options and Project Options but the options by themselves are still there.