XSS (Cross Site Scripting)

👉 Overview

👀 What ?

Cross-Site Scripting, abbreviated as XSS, is a common security vulnerability typically found in web applications. It occurs when an application includes untrusted data in a new web page without proper validation or escaping, allowing an attacker to inject malicious scripts into web pages viewed by other users.

🧐 Why ?

Understanding XSS is crucial in the field of cybersecurity as it is a common attack vector that can lead to serious consequences if not properly addressed. These consequences include identity theft, data breaches and other serious harm to an organization's security posture. Therefore, it is important to understand what XSS is, how it works and how it can be prevented.

⛏️ How ?

To exploit an XSS vulnerability, an attacker injects malicious scripts, often written in JavaScript, into a website that fails to properly validate user input. This script can then be executed in the browser of another user, leading to a range of possible attacks, from stealing session cookies to performing actions on behalf of the user. To prevent XSS attacks, it is essential to properly validate and escape all user input, use appropriate response headers, and implement Content Security Policies (CSP).

⏳ When ?

XSS vulnerabilities have been known and exploited since the early days of the internet, but have become increasingly prevalent with the growth of dynamic web applications. Despite increased awareness and more sophisticated defense mechanisms, XSS remains a major threat to web security.

⚙️ Technical Explanations

From a technical standpoint, XSS attacks are divided into three types: Stored, Reflected, and DOM-based XSS. Stored XSS, also known as Persistent XSS, occurs when the malicious script is permanently stored on the target server. Reflected XSS occurs when the malicious script is embedded in a URL. DOM-based XSS occurs when an application’s client-side script writes user-provided data to the Document Object Model (DOM). The user’s browser then executes the data as script. Each type requires different prevention techniques, highlighting the importance of a comprehensive understanding of XSS and its mechanisms.