Recently I wrote a quick HowTo about dealing with using Burp Suite against an application that invalidates your session whenever it spots a potential malicious payload. I wrote that a Burp Macro that can perform Automatic Reauthentication can overcome that issue. Another common issue that gets in the way of performing penetration tests against mobile applications is having to deal with anti cross-site request forgery tokens. These are tokens that an application embeds in a response and expects to see in the body of the subsequent request, if the token is ever missing or incorrect the request is ignored. This interferes terribly with Burp Suite tools such as repeater, intruder and scanner as by default these don’t handle the tokens and therefore the requests are all ignored. I get around this issue through the use of simple custom burp extensions and I wanted to share some notes about how surprisingly simple this is!
I wrote a very simple burp extension that can pull a token a CSRF token out of a response and update the next request with that token. It’s designed to be a simple as possible so it works for my lesson on writing burp extensions and if you’re lucky then all you need to do is update the script with the name of the token your target application uses and you’re good to go but it’s designed to be as easy to tweak to your needs as possible. I also wrote about how to install custom extensions here if you’ve not done that before, just copy and paste the below code into a file called csrftei.py and load that file into burp! The code is all available below and should be nicely commented to explain how everything works:
During a recent penetration test I came up against a security feature that would invalidate my session whilst I was fuzzing if it saw simple attack strings, so if I used <script> anywhere then it’d kill my session. Most frustrating! Especially as it essentially prevented the use of tools such as Burp’s Active Scanner and it made using Repeater inconvenient too. So I quickly threw together a Burp Macro to handle automatic re-authentication for me and went back to fuzzing!
So here’s how to do that!
Effectively filtering user input is one of the best ways to prevent an awful lot of web application vulnerabilities. There are several ways to approach this, each with their own pros and cons so I’ll run through them here an then you can think of the best way to combine them for your context. It’s important to remember though, that filters are context specific, there is not one filter that will work for a whole application and that’s what can make writing an effective filter tricky.