What Is Cross-Site Scripting (XSS)? A Complete Guide

What Is Cross-Site Scripting (XSS)? A Complete Guide

Cross-Site Scripting (XSS) is one of the most common web application vulnerabilities. It allows attackers to inject malicious JavaScript into web pages viewed by other users, potentially leading to stolen sessions, credential theft, or website defacement.

Types of XSS

Stored XSS

Malicious code is permanently stored on the target server, often inside comments, forums, or user profiles.

Reflected XSS

The malicious script is included in a URL or request and immediately reflected back to the victim.

DOM-Based XSS

The attack manipulates the browser's Document Object Model (DOM) without modifying the server response.

Risks

Successful XSS attacks can:

• Steal cookies
• Hijack user sessions
• Redirect visitors
• Display fake login forms
• Execute malicious JavaScript

Prevention

Developers should:

• Validate all user input.
• Escape HTML output.
• Use Content Security Policy (CSP).
• Sanitize data before rendering.
• Keep frameworks updated.

Testing Tools

Popular tools include:

• Burp Suite
• OWASP ZAP
• XSStrike

Conclusion

Cross-Site Scripting remains one of the most exploited web vulnerabilities. Understanding how it works is essential for developers and security professionals alike.