$25k GitHub account takeover & justCTF 2023 CSRF+XSS writeup

Summary

This video explores the nuances of web application security vulnerabilities, highlighting how developers' assumptions can lead to security flaws. The presenter demonstrates two examples, one involving a GitHub account takeover that earned a $25,000 reward, and another showcasing a CTF challenge. The video delves into the intricacies of CSRF protection, the misuse of the HEAD method in frameworks, and the critical distinction between tokenizing and parsing in sanitization processes, which can inadvertently introduce XSS vulnerabilities. The speaker also invites viewers to participate in an upcoming CTF event to sharpen their hacking skills, emphasizing the importance of understanding these concepts in web security.

Takeaways

• 🔒 Every security vulnerability often stems from a developer's incorrect assumption or an unexpected behavior from frameworks.
• 🎯 The speaker created a CTF challenge inspired by a $25,000 GitHub account takeover incident.
• 🛤️ In web applications, routes are typically defined by specifying the path, methods, and the function to handle requests, with CSRF protection often applied to state-changing requests.
• 🔄 The HEAD method in HTTP can sometimes bypass CSRF protection if frameworks treat it similarly to GET, despite differences in request handling.
• 🤹‍♂️ The speaker invites participants to a CTF event organized by their team, justCatTheFish, emphasizing the opportunity to develop hacking skills.
• 📅 The online teaser for the CTF event is scheduled from June 15th for 24 hours, with a link provided in the description for registration.
• 🙏 Sponsors such as Trail of Bits, OtterSec, HexRays, and SECFORCE are acknowledged for their support, with links to them in the description.
• 🕵️‍♂️ The script discusses the nuances of sanitization in web applications, highlighting the difference between tokenizing and parsing HTML inputs.
• 🧩 The mistake in the script's example was not in the sanitization logic but in how the input was tokenized, leading to a potential XSS vulnerability.
• 🌐 The importance of understanding HTML namespaces is underscored, as tags behave differently across namespaces, affecting the effectiveness of security measures.
• 🎖️ The final payload in the script's example exploits an XSS vulnerability, which could be used to exfiltrate sensitive information like flags in a CTF challenge.
• 📚 The speaker encourages viewers to check out another video for a write-up on a SQL injection task, providing a link on the screen.

Q & A

What is the primary cause of security vulnerabilities in web applications according to the video?

The primary cause of security vulnerabilities in web applications is developers making wrong assumptions, either through their own mistakes or due to the unexpected behavior of frameworks.

What is the purpose of the CTF challenge mentioned in the video?

The purpose of the CTF challenge is to demonstrate two examples of security vulnerabilities inspired by a $25,000 reward account takeover on GitHub, and to encourage participants to develop their hacking skills.

How does the CSRF protection work in the context of the video?

CSRF protection works by automatically requiring a CSRF token for all POST, PUT, DELETE, and other requests that are intended to change something on the server. It is not required for GET requests, which are only supposed to serve the response.

Why is the HEAD method significant in the context of the video?

The HEAD method is significant because many frameworks treat it the same as GET during the routing stage, but it can bypass CSRF protection if the if statement in the function checks specifically for GET, allowing access to the block of code that should be protected.

What is the difference between tokenizing and parsing in the context of the video?

Tokenizing is the process of breaking down code into tokens without applying namespace rules, while parsing applies these rules, which can lead to different outcomes especially when dealing with namespaces like SVG that can alter the behavior of tags.

How does the video explain the exploitation of the XSS vulnerability?

The video explains that the exploitation of the XSS vulnerability occurs when the sanitizer's tokenization process fails to recognize an XSS payload within an SVG namespace, allowing the script to execute in the browser.

What is the role of the 'textarea' tag in the context of the XSS vulnerability discussed in the video?

In the HTML namespace, the 'textarea' tag can only contain text, making it resistant to XSS payloads. However, when wrapped in an SVG tag, changing the namespace, it becomes vulnerable to XSS attacks.

What is the significance of the 'script' tag in the XSS vulnerability discussed?

The 'script' tag is significant because it is used to execute JavaScript code. In the video, it is shown that when the 'script' tag is within an SVG namespace, it can bypass sanitization and lead to an XSS attack.

What is the role of the CTF challenge organizer 'justCatTheFish' in the video?

The role of 'justCatTheFish' is to organize the CTF challenge, provide a platform for participants to develop their hacking skills, and to offer a new task for the current year's competition.

How can participants join the CTF challenge mentioned in the video?

Participants can join the CTF challenge by following the link provided in the video description, which leads to the event's registration or information page.

What is the significance of the sponsors mentioned in the video?

The sponsors, Trail of Bits, OtterSec, HexRays, and SECFORCE, are significant because they support the CTF challenge, making it possible for the event to occur and providing resources for the participants.