Cross-Site Scripting (XSS) Explained

Key Concepts

Cross-Site Scripting (XSS) is a type of security vulnerability typically found in web applications. The key concepts include:

• Definition and Purpose
• Types of XSS
• Impact of XSS
• Common Attack Vectors
• Preventive Measures

Definition and Purpose

XSS occurs when an attacker injects malicious scripts into a web page viewed by other users. This can lead to unauthorized actions, data theft, and other malicious activities.

Types of XSS

There are three main types of XSS:

• Stored XSS: Malicious scripts are permanently stored on the target server and executed when users request the data.
• Reflected XSS: Malicious scripts are reflected off the web server, typically through a URL parameter.
• DOM-based XSS: Malicious scripts are executed due to modification of the Document Object Model (DOM) environment in the victim's browser.

Impact of XSS

The impact of XSS can be severe, including:

• Session hijacking
• Data theft
• Defacement of web pages
• Propagation of malware

Common Attack Vectors

Common attack vectors for XSS include:

• Input fields (e.g., search boxes, comment sections)
• URL parameters
• HTTP headers

<input type="text" name="search" value="<script>alert('XSS')</script>">
    

Preventive Measures

Preventive measures to mitigate XSS include:

• Input validation and sanitization
• Output encoding
• Content Security Policy (CSP)
• Use of modern frameworks with built-in XSS protection

function sanitizeInput(input) {
    return input.replace(/<script>.*?<\/script>/gi, '');
}
    

Examples and Analogies

Imagine XSS as a malicious graffiti artist:

• Definition and Purpose: The graffiti artist sneaks into a public space to deface it.
• Types of XSS: The graffiti can be permanent (stored), temporary (reflected), or hidden (DOM-based).
• Impact of XSS: The graffiti can mislead people, steal their belongings, or spread harmful messages.
• Common Attack Vectors: The graffiti artist targets public boards, signs, and walls.
• Preventive Measures: Regular cleaning, surveillance, and protective coatings can prevent graffiti.