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Stored DOM XSS (المستوي المتوسط) | تعلم الامن السيبراني - Bug Bounty

Introduction

In the name of God, the Most Gracious, the Most Merciful. Welcome to Lesson 18 of the Web Application Testing course. Today, we will delve into the topic of Stored Domain XSS, following our previous lesson on Reflective Domain XSS.

Introduction to Stored DOM XSS

In this lesson, we will explore the vulnerabilities related to Stored DOM XSS, which occurs when an application stores malicious scripts in the database and later retrieves and executes them in the browser without proper validation or sanitization. Understanding this vulnerability is essential for anyone looking to become proficient in web application security and bug hunting.

Analyzing a Blog Application for Vulnerabilities

Our case study today is a blog application that allows users to submit comments on posts. We will examine how an attempt to input HTML or JavaScript code in a comment may lead to vulnerabilities.

  1. Initial Testing: First, we navigate to the blog and select a post. We will attempt to input HTML code, such as an <h1> tag, into the comments section. Once submitted, we will observe how the application handles our input.

  2. Unexpected Behavior: Upon reviewing the comment, we observe that while the first <h1> is rendered on the page, the closing </h1> tag does not appear. This behavior indicates that the application may be mishandling user input.

  3. Using a Proxy Tool: To further investigate, we will utilize a tool like Burp Suite to capture HTTP requests. We can analyze the JavaScript files responsible for rendering comments.

  4. Exploring JavaScript Functions: Within the JavaScript code, we identify a function named EscapeHTML(). This function is designed to prevent script execution by converting HTML special characters into their encoded counterparts. However, we notice that this function only escapes the first instance of certain characters.

  5. Understanding the Vulnerability: The significant issue arises because the EscapeHTML() function fails to process multiple instances of harmful input correctly. This allows us to exploit the situation by entering the same character sequence more than once, which can lead to script execution in the browser.

Exploit Submission After discovering this flaw, we can craft our payload to ensure that only the first instance of our input is escaped while potentially allowing subsequent instances to be executed. Our test demonstrates that by submitting crafted input that includes JavaScript, we can successfully trigger an alert, confirming the presence of the vulnerability.

Conclusion Through our analysis of this blog application's comment functionality, we successfully identified and exploited a Stored DOM XSS vulnerability. This lesson reinforces the importance of input validation and proper encoding to safeguard against user-generated content exploitation.

Remember, as aspiring bug bounty hunters or security testers, it is crucial to continuously practice these techniques while adhering to ethical guidelines.

Keyword

  • Stored DOM XSS
  • Web Application Testing
  • Bug Bounty
  • HTML Injection
  • EscapeHTML Function
  • Client-side Scripting
  • Security Vulnerabilities

FAQ

Q1: What is Stored DOM XSS?
A1: Stored Domain XSS is a type of vulnerability where malicious scripts are stored in the database and later executed in a user's browser without proper filtering or encoding.

Q2: How can I test for Stored DOM XSS vulnerabilities?
A2: You can test for Stored DOM XSS by submitting malicious input, such as HTML or JavaScript code, through forms and observing how the application renders the content.

Q3: Why is input validation important in web applications?
A3: Input validation is essential as it prevents attackers from injecting harmful code that can compromise security and lead to unauthorized actions on the site.

Q4: What tools can assist in identifying XSS vulnerabilities?
A4: Tools like Burp Suite and OWASP ZAP can help capture HTTP requests and analyze how a web application processes user input.

Q5: What are best practices to prevent DOM XSS?
A5: Best practices include using secure coding practices, properly encoding output, implementing Content Security Policies (CSP), and conducting regular security audits.

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