Security

I got first blood for a challenge called “safelist” in SekaiCTF 2022, it’s a challenge about xsleaks and request timing in particular, here is my writeup.

Challenge description:

Safelist™ is a completely safe list site to hold all your important notes! I mean, look at all the security features we have, we must be safe!

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When it comes to CSP bypass, a kind of technique using AngularJS is well-known. One of it’s variant requires another library called Prototype.js to make it works.

After understanding how it works, I began to wonder if there are other libraries on cdnjs that can do similar things, so I started researching.

This article will start with the CSP bypass of cdnjs, talk about why prototype.js is needed, and then mention how I found its replacement on cdnjs.

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At first, I had no intention of writing a post about this challenge because the author already had a greate one: corCTF 2022 Challenge Writeups. But, it’s my first time being the only solver for a challenge, it’s still worth writing one.

In this post, I will talk about how I tackled the challenge in the first place and how I solved it in the end.

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We all heard about insecure deserialization vulnerability and saw many real-world cases in Java, PHP, and other languages.

But, we rarely hear about this vulnerability in JavaScript. I think it’s because the built-in serialization/deserialization function JSON.parse and JSON.stringify are only for basic data structures like string, number, array and object.

Class and function are not supported, so there is no way to run malicious code during deserialization.

What if we implement our deserialization logic and support class and function? What could possibly go wrong?

GoogleCTF 2022 has a web challenge called “HORKOS,” which shows us the way.

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I didn’t check all the challenges this time because when I joined the competition, most of the challenges already solved by my teammates lol

I love JavaScript(yep, including those weird features) and XS-leak, so this writeup will talk about only two challenges:

  1. web/Sustenance
  2. misc/CaaSio PSE

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Among the many web vulnerabilities, my favorite is prototype pollution. It can be powerful sometimes when you find a script gadget.

So, I decided to make an XSS challenge about prototype pollution.

In April, the challenge I made was released on Intigriti, if you haven’t checked that one, here is the link: https://challenge-0422.intigriti.io/

Making a good challenge is hard.

I made a few mistakes. With the bugs I made, the challenge became much easier. To make up for it, I decided to make another one, called “The Revenge of Intigriti 0422 Challenge”.

Below is the intended solution to the revenge challenge.

Challenge URL: https://aszx87410.github.io/xss-challenge/revenge-of-intigriti-0422

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