Among the various data types in JavaScript, Number is a very commonly used one, and there are some small details that need to be paid special attention to, otherwise it is easy to write code with bugs.
This article will show you some examples, some are hypothetical scenarios, and some are problems I have encountered myself. Before continuing to explain each case, you can try to put yourself in the scenario and think about whether you know the cause of the problem and how to avoid it.
Last weekend, in addition to the SUSCTF 2022 I wrote about in my previous post, there was also another TSJ CTF with many good challenges. Due to time constraints, I only chose the ones that interested me more, and this is the Nim Notes challenge mentioned in the title. I didn’t manage to solve it in the end (I was far from it), but the solution was very interesting, so I’m writing this post to record the official solution.
The author’s (maple3142) writeup is here: https://github.com/maple3142/My-CTF-Challenges/tree/master/TSJ%20CTF%202022/Nim%20Notes
This holiday there were several CTFs, and I participated in SUSCTF 2022 with team SU. This post briefly records my experience with several of the challenges I participated in.
The list of challenges I will discuss is as follows:
How many data types are there in JavaScript? And what are they?
Before discussing data types, we should first know how many types there are in JavaScript and have a basic understanding of each type. Before we start, you can count them yourself and then compare your answer with mine to see if it is correct.
As JavaScript evolves, this article will use the latest ECMAScript 2021 as the standard. If “spec” is mentioned below, it refers to the ECMAScript 2021 language specification .
In May 2021, I solved my first Intigriti XSS challenge. Since then, I play every XSS challenge afterward, and solved most of them. Sometimes it’s painful when you try everything you know but still can’t solve it, however, the moment you made it, the pain is gone, replaced with joy and happiness.
As a player, I want to be on the other end(as a challenge maker) at least once, if I have an idea of an interesting XSS challenge.
I talked to @PinkDraconian in Jan 2021 and share an XSS challenge I created, after a few discussions, it gets accepted. This write-up is about the story behind the challenge.
I believe that in order to understand the JavaScript programming language, it is important to understand the concept of the “execution environment” or “runtime”. Many people are not aware of this concept, which can lead to differences in understanding of JavaScript or other technologies. Therefore, in this article, let’s talk about the execution environment.
Note: In addition to “runtime”, “execution environment” is also used to refer to the same concept, but these two terms are completely different. To avoid confusion, we will use the term “runtime” throughout this article.
Also, “runtime” has many meanings, but in this context, it refers to the runtime environment.
If you don’t know what CTF is, you can refer to my previous article: How to Get Started with Web Challenges in CTF?, which briefly introduces what CTF is and some basic types of challenges.
I played DiceCTF 2021 seriously last year and finally solved 6 web challenges. My experience is here: DiceCTF 2021 - Summary. I took a look at this year’s DiceCTF and was completely shocked. The difficulty level is completely different.
There are a total of 10 web challenges this time, with 1 easy challenge solved by 365 teams, another relatively simple one solved by 75 teams, and the other 8 challenges solved by only 5 teams or less, with one of them unsolved.
As a person who likes web and JS-related tips, this is a great learning opportunity to learn various techniques through the writeup released after the competition. There won’t be notes on all web challenges below, only the ones I’m interested in.
Glints is a job search platform based in Singapore, and they just got a 20M investment last year, they have a team in Taiwan as well.
In July 2021, I found Glints bug bounty program so I spent some time on it, and I found 4 vulnerabilities in total in the end.
The vulnerabilities I found could have:
In other words, the attacker can steal all users’ information by exploiting the vulnerabilities.
Let’s see what it is.
If your website wants to experience new features that have not yet been officially launched by the browser, what should you do?
Usually, these features are already available, but not yet open. Therefore, browsers provide some flags that can be turned on and off. As long as the switch is turned on, you can experience the new features in advance. However, we usually cannot ask users to turn on the switch themselves.
Therefore, Chrome provides a mechanism called origin trials. You can register on the website to obtain a set of tokens. After setting it up, if the user visits your website with Chrome, the new feature will be turned on, allowing your website to use it.
This article will briefly introduce how to use this mechanism.
After discussing the history and baggage of JavaScript, let’s talk about JavaScript itself.
Have you ever wondered how to know if an author of a JavaScript book or tutorial article has written it correctly? How do you know if the knowledge in the book is correct? As the title suggests, could it be that the JavaScript knowledge you previously knew was actually wrong?
Do you just trust the author because they often write technical articles? Or do you believe it because it’s written the same way on MDN? Or is it because everyone says it, so it must be right?
Some questions do not have standard answers, such as the trolley problem, where different schools of thought will have their own approved answers, and there is no saying which one is necessarily correct.
Fortunately, the world of programming languages is relatively simple. When we talk about JavaScript knowledge, there are two places where you can verify whether this knowledge is correct. The first is called the ECMAScript specification, and the second one, we’ll talk about later.