Introduction
I couldn’t solve the challenge for June, so I’m going to learn from other people’s writeups and review where I can improve.
When it comes to XSS (Cross-site scripting), many people may only think of “injecting code into a website”. However, if you think about it carefully, you will find that there are many aspects that can be further explored.
These “aspects” can also be understood as different “levels”.
For example, the first level is to prevent your website from being attacked by XSS, and not allowing attackers to inject code into the website. The act of “allowing attackers to inject code into the website” can be further divided into different types of injection, such as HTML injection, injection in HTML element attributes, or injection in JavaScript code. Each of these has different attack and defense methods.
In addition to preventing code injection, the defender should also think further: “What if code injection does occur?”
This is the second level. Although we have done our best to prepare for the first level, vulnerabilities may still occur. Therefore, it is not enough to defend the first level, and we must also defend the second level.
Suppose an attacker has found a place to inject code. Can we find a way to prevent it from executing? This is where CSP (Content Security Policy) comes in, by setting some rules to prevent illegal code from executing. For example, inline JavaScript can be prevented from executing, making <img src=x onerror=alert(1)> ineffective.
If the attacker is really skilled and can bypass the rules of CSP, then we enter the third level. The assumption of the third level is that the attacker can execute any code on the website.
What can we defend against at this point? It is to try to minimize the damage.
For example, for platforms like Medium, if an attacker can use XSS to take over someone else’s account, it is a serious vulnerability. Or, because Medium has a paywall feature, if an attacker can transfer money to their account through XSS, it will also be a serious problem.
We must try to defend against these attacks under the premise of “the website has already been attacked by XSS”.
Next, let’s take a look at the different defense methods for different levels.
I was recently tasked with generating a PDF report. There are many ways to create a PDF, such as using Word and then converting it to PDF. However, my first thought was to write it as a web page and then use the print function to convert it to PDF.
At my previous company, I saw a project that used JS to generate PDFs using PDFKit. While it had a high degree of flexibility, I found it difficult to maintain. The reason is that using this tool is like drawing a PDF, and you have to specify (x, y) coordinates to draw something. Changing a small part may require changing many lines of code.
At the time, I thought, why not just use the simplest HTML + CSS, cut the layout, and then convert it to PDF? If you don’t want to convert it manually, you can also use headless chrome to convert it. Because it is a web page, it should be easy to maintain. Moreover, because the layout is done using HTML and CSS, it should be much simpler than drawing.
It wasn’t until I later encountered web-to-PDF conversion that I realized things weren’t as simple as I thought.
Intigriti is a foreign bug bounty platform that releases an XSS challenge every month. Participants have about one to two weeks to think about it, and the goal is to execute alert(document.domain) on a specific website. After solving the challenge, the results are reported through the Intigriti platform, and three randomly selected winners will receive coupons for their own store.
Last month’s challenge had few winners, so I was lucky enough to win a €50 coupon. It was actually a good deal because the items in the store were quite cheap. I bought a t-shirt, two hats, and international shipping for about €45.
However, this kind of prize is based on luck, and solving the problem is more important than winning.
The challenge URL is here: https://challenge-0521.intigriti.io/
One day, while browsing the internet, I came across an XSS challenge: Intigriti’s 0421 XSS challenge - by @terjanq. Apart from the challenge itself being very attractive, what attracted me more was the author who created it.
Many of the security-related resources I found online that were more focused on front-end were maintained or contributed to by this author, such as Tiny XSS Payloads or the eye-opening XS-Leaks Wiki.
Intigriti seems to hold this kind of XSS challenge every month, and this was the hardest one they have ever held. The challenge lasted from 4/19 to 4/25, with a week to try, and only 15 people successfully solved it. In March, 45 people solved the challenge, and in February, 33 people did, so the number of people who solved it this time was indeed much less, indicating the difficulty of the challenge.
I spent about five days on it, and every time I got stuck, I thought, “I should give up and wait for the answer.” But then, from time to time, new ideas would come up, and I would try again. Finally, on the last day before the deadline, I solved it before the time limit, and when I did, I clenched my fists and shouted, “Too awesome!”
This article is about my experience in solving the challenge. I previously wrote an English version, but it was probably worse than an elementary school composition, so I decided to write a Chinese version to better express my thoughts. The title will have a “Part 1” because this article is about my solution, and the next article will be about the author’s solution, and the one after that will analyze other people’s solutions.
But it seems that my blog is cursed to break the series of articles that haven’t been written yet, so I hope I can make it through this time.
If you don’t know what XSS (Cross-site Scripting) is, in simple terms, it is when a hacker can execute JavaScript code on your website. Since it can be executed, it is possible to steal the user’s token, impersonate the user’s identity to log in, even if the token cannot be stolen, it can still modify the page content, or redirect the user to a phishing website, and so on.
To prevent XSS, it is necessary to prevent hackers from executing code on the website, and there are many ways to defend against it. For example, CSP (Content-Security-Policy) can be used as an HTTP response header to prevent the execution of inline scripts or restrict the domains from which scripts can be loaded. Trusted Types can also be used to prevent some potential attacks and specify rules, or use some libraries that filter XSS, such as DOMPurify and js-xss.
But is it enough to use these? Yes and no.
If used correctly, of course, there is no problem, but if there are incorrect settings, there may still be XSS vulnerabilities.
Recently, I just transferred from a company to a cybersecurity team, Cymetrics, and when I was researching some websites, I found a ready-made case. Therefore, this article uses this ready-made case to illustrate what is called incorrect settings and what impact this setting will have.
After writing CSS for a while, we should all be familiar with common properties such as display, position, padding, margin, border, background, etc. We can write them smoothly without having to look up anything.
These properties are common because they are used in many places. However, some CSS properties can only be used in specific places or under specific circumstances. I often forget these less commonly used properties, but they are actually very important in some cases.
Therefore, in this article, I want to introduce some CSS properties that I think are not easy to remember but are very useful. This is also a note for myself.
Whenever I start a JavaScript-related project, my go-to setup is usually ESLint + Prettier. If you haven’t heard of them, let me briefly explain. Prettier is used to format your code, so you don’t have to argue with others about whether to add semicolons, whether to break { for if blocks, or how many characters per line. With Prettier, you let it decide (although there are configuration files you can adjust).
This is actually quite helpful for teams because it unifies the code format, and the basic coding style will be consistent. Although ESLint also has some formatting-related parts, it focuses more on best practices when writing code, such as declaring variables before using them and using const for variables that won’t change. This is beyond the scope of formatting.
Therefore, using ESLint with Prettier can ensure the minimum quality of the entire codebase, at least avoiding terrible formatting. The most common rule people use with ESLint is probably the Airbnb JavaScript Style Guide, which explains each rule in detail.
When I was writing code before, I suddenly thought of a place where ESLint might be suitable, so I tried it out and found that making a “usable” plugin was easier than I thought. This article records the process and experience.
This article has a little less technical content, and I would like to share with you the process of writing this series of articles and some thoughts after finishing it.
If you haven’t read this series of articles yet, the links are as follows:
In the previous articles, we learned that the CORS protocol is essentially a security protocol. In addition to CORS, there are actually a series of things related to cross-origin, such as:
Doesn’t just seeing this series of similar terms make you dizzy? Yes, me too. In the process of organizing this information, I found that the security issues related to cross-origin are more complicated than I thought, but after spending some time organizing them, I found that there is still a logical sequence to follow. Therefore, this article will explain why these things appear in a context that I think should be easier to understand.
In addition to the various COXX things mentioned above, there are other cross-origin related security issues that I want to mention in this article.
Before we continue, I would like to remind everyone that this article is about “security issues of cross-origin”, not just “security issues of CORS”. The things protected by the CORS protocol and their content have been introduced before. What this article is going to talk about is actually somewhat deviating from the main title “CORS” complete guide, because this is not very related to the CORS protocol, but rather raises the level again and talks about “cross-origin” itself.
So when you read the following things, don’t confuse them with CORS. Except for the first thing to be discussed later, the others are not very related to CORS.