Due to being busy lately, I haven’t been participating in CTFs as much in the past two or three months. However, I still come across some interesting challenges on Twitter. Even though I don’t have time to solve them, I still take notes because if I don’t, I won’t be able to solve them later for sure.

This post mainly documents some web front-end related challenges. Since I might not have personally solved them, the content is based on references from others’ notes, with some personal insights added.

Keyword list:

  1. copy paste XSS
  2. connection pool
  3. content type UTF16
  4. multipart/mixed
  5. Chrome DevTools Protocol
  6. new headless mode default download
  7. Scroll to Text Fragment (STTF)
  8. webVTT cue xsleak
  9. flask/werkzeug cookie parsing quirks

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On November 9, 2023, Sentry published an article on their blog titled Next.js SDK Security Advisory - CVE-2023-46729. The article discusses the details of the CVE-2023-46729 vulnerability, including its cause, discovery time, and patching time.

Although the vulnerability was officially announced on 11/9, it was actually fixed in version 7.77.0 released on 10/31. Some time was given to developers to patch the vulnerability.

Now let’s briefly discuss the cause and attack method of this vulnerability.

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Both of these competitions had many interesting but challenging problems. I really learned a lot.

Keyword list:

  1. nim json, null byte
  2. nim request smuggling
  3. js-yaml
  4. web worker
  5. blob URL
  6. meta redirect
  7. file protocol & .localhost domain
  8. sxg: Signed Exchanges
  9. 431 CSP bypass
  10. DOM clobbering document.body
  11. ejs delimiter
  12. Node.js + Deno prototype pollution gadget
  13. XSleaks golang sort

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I participated in both of these events to some extent, but I didn’t look at every challenge. This post is just a note to briefly record the solutions, without going into too much detail.

As usual, here are the keywords I noted:

  1. GraphQL batch query + alias
  2. Python os.path.join absolute path
  3. Svg XSS, foreignObject
  4. WebRTC CSP bypass
  5. Status code xsleak
  6. DNS rebinding
  7. nmap command injection
  8. Ruby rack file upload temporary storage
  9. buildConstraintViolationWithTemplate EL injection
  10. Request smuggling
  11. document.baseURI
  12. 200/404 status code xsleak

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A while ago, I was busy traveling and didn’t have much time for CTFs. Even if I did participate, I was too lazy to write a writeup, so my last writeup was back in March. I felt it was a shame to break the streak, so I quickly wrote another one to make up for it.

Regarding the three CTFs mentioned in the title, I only participated in GoogleCTF 2023. For the other two events, I only briefly looked at the challenges, so this post will only serve as a note on the challenges and their solutions.

Keyword list:

  1. Inconsistent order of POST data parsing between Flask and PHP
  2. iframe CSP blocking certain script loads
  3. CSRF bypass using HEAD method
  4. Accessing parent origin using location.ancestorOrigins
  5. Changing iframe location doesn’t affect the src
  6. Angular CSP bypass gadget in recaptcha URL
  7. Restoring input using document.execCommand('undo');
  8. X-HTTP-Method-Override
  9. Differences between HTML and XHTML parsers

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Originally, I intended to write this article from a developer’s perspective. However, due to time constraints, I will first write a CTF-oriented article to record this issue. I will write from a developer’s perspective when I have more time.

In short, this article discusses the problems caused by using the following pattern:

const express = require('express')
const app = express()
const port = 3000

app.set('view engine', 'ejs');

app.get('/', (req,res) => {
    res.render('index', req.query);

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`)

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Regular expressions (hereinafter referred to as regexp), are mainly used for string matching. After writing a pattern, it can be used to match text that meets the rules.

Whether it’s a phone number, email, or ID number, regexp can be used to perform basic format validation to ensure that the string format matches specific rules.

Although regexp is convenient, if it is not written properly, it may cause some input validations to be bypassed and evolve into a security issue. In addition to this, there is another type of problem that will cause issues, which is ReDoS, the full name is: Regular expression Denial-of-Service, due to the denial of service attack caused by regular expressions.

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In the previous articles, we talked about static analysis, which means we didn’t actually run the app. Instead, we studied the logic of the app’s operation through decompiled code and modified the code before repackaging and executing it.

Dynamic analysis, on the other hand, means that we will run the app and use various methods to hook various methods to monitor the input and output of certain methods, and even tamper with them.

In this article, let’s learn how to use Frida for dynamic analysis.

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I remember when I first started working with Android, it was easy to see which requests an app was sending. All I had to do was install Charles on my computer, set up the Wi-Fi on my phone to proxy to my computer, and then download the certificate provided by Charles by entering a specific URL. Once installed, I was good to go.

However, when I tried the same process recently, I could see some packets being sent, but the traffic coming out of the app was empty. I searched online for various solutions, but none of them worked.

Finally, I found out that Android changed its security settings above 6.0, and by default, it does not trust certificates installed by users, which is why it cannot intercept them. One solution is to install a local VPN, which will route all traffic through the proxy, but I found it a bit cumbersome after trying it out.

Among the many methods, the most useful one I tried was to unpack the apk, modify some settings, and then repack it. This article will document the process and experience.

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