WebApp 101

Panning for Gold in JavaScript Files Using Burp Suite and Grep

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As part of a webapp pentest, or when hunting for bug bounties, being able to find API endpoints, URIs, and sometimes even commented credentials/API keys through Javascript files is a good skillset to have. Luckily, using Burp Suite and Grep, it’s pretty trivial to hunt for this information.

Note: This post is fairly incomplete and will be updated as time goes on.

To begin, make sure you have your Burp Suite project capturing data as you browse the application. Manually crawl the website by navigating to every page and feature that you can find. Then, have Burp Suite crawl the page and do some enumeration of its own. Don’t skip this part, and make sure you do a thorough job, or you may be leaving Javascript files undiscovered.

Once properly enumerated, let’s extract all of the scripts that we can. This can be done by navigating to the Target tab, and selecting Site Map. Right click the target URL, head over to Engagement Tools, and then select Find Scripts.

Let’s start by updating our box installing Pip, and installing JavaScript Beautifier.

sudo apt update -y && sudo apt upgrade -y
sudo apt install python3-pip -y
sudo pip3 install jsbeautifier

Once you have the tool installed, run it specifying your input and output files.

js-beautify -o beautify.js input.js

Now that the output in cleaned up, you can get started grepping through it for gold!

Helpful grep commands

To find all that contain cmsapi:
grep --color -E "'\/cmsapi\/[^']+'" beautify.js

To find all items between single or double quotes:
grep --color -E "'\/[^']+'|\"\/[^\"]+\"" beautify.js

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