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Reflected XSS into a template literal (المستوي المتوسط) | Bug Bounty

Introduction

Welcome to a new lesson from the Web Application Training Testing course. In this intermediate-level tutorial, we will explore the vulnerability known as Reflected XSS (Cross-Site Scripting) and how it can be exploited when dealing with template literals in JavaScript.

Introduction to Reflected XSS

Before diving into technical details, it’s important to acknowledge that tackling this vulnerability may seem challenging at first. It's entirely normal not to find the solution immediately. Remember, education involves a learning curve!

The platform we will use for this lab is PortSwigger, which provides an excellent environment to hone your skills. Each lab covers a unique aspect of web security, so don’t be discouraged if you struggle initially. In fact, seeking out explanations is a valuable part of mastering any subject.

What is a Template Literal?

A template literal is a special type of string in JavaScript, delineated by backticks ( ` ). Unlike standard string notation using single (') or double (") quotes, template literals allow for multi-line strings and complex expressions. This feature makes it easier to embed variables and expressions directly within a string.

Understanding the Lab

In this lab, you need to identify how the vulnerable function processes inputs and how it can be exploited using a reflective XSS payload. The search block function is affected by the XSS code, and there are specific protections in place, including HTML encoding and escape characters like single and double quotes.

Task: Your objective is to implement an alert function using the template literal.

Exploitation Steps

  1. Navigate to the vulnerable search box and input any value.
  2. After submitting, check where your input has been reflected. You’ll find it displayed within HTML tags, particularly inside an H1 element and JavaScript code.
  3. To exploit the XSS vulnerability, you need to analyze the JavaScript code, which is wrapped in template literals.

Use Visual Studio Code for better readability and to understand the structure of the code. Look for places in the JavaScript code where you can insert your payload.

Crafting Your Payload

You can use the dollar sign ($) followed by curly braces (()) to execute JavaScript expressions within the template literal. For instance, to trigger an alert, you simply need to write:

`$(alert('Your message here'))`

By injecting this code into the search box, you can successfully execute the alert function, demonstrating the reflected XSS vulnerability in action.

Conclusion

By following these steps, you’ve interacted with a vulnerable application and used your understanding of template literals to exploit a reflected XSS vulnerability. This hands-on approach is essential for reinforcing your skills in web application security.

If you have any questions, feel free to leave them in the comments, and I’ll respond to all inquiries. In our next lesson, we will dive into XSS Blind, where we will learn new tactics to exploit this particular vulnerability.

Until then, happy hacking!

Keywords

  • Reflected XSS
  • Template Literal
  • PortSwigger
  • JavaScript
  • Vulnerability
  • Exploitation
  • Alert Function
  • Multi-line Strings
  • Security Testing

FAQ

Q1: What is Reflected XSS?
A1: Reflected XSS is a type of cross-site scripting vulnerability where an attacker can inject malicious scripts that are reflected off a web server and executed in a user's browser.

Q2: What are template literals in JavaScript?
A2: Template literals are strings enclosed by backticks ( ` ), allowing for multi-line strings and the embedding of expressions.

Q3: How do you identify vulnerabilities in a web application?
A3: Vulnerabilities can be identified through security testing tools (like PortSwigger), analyzing code, and manual testing of input fields for unexpected behavior.

Q4: What is the purpose of escaping characters?
A4: Escaping characters (like single and double quotes) is a security measure to prevent injection attacks by ensuring that the inputs are treated as safe data rather than executable code.

Q5: How can I practice and improve my skills in web application security?
A5: Engage with platforms like PortSwigger, participate in Capture The Flag (CTF) challenges, and continuously review past lessons and exploits to reinforce your knowledge.

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