What Is Cross-Site Scripting and Its Types?


Larry Thompson

Cross-Site Scripting (XSS) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This article will explore the different types of XSS attacks and provide insights on how to prevent them.

What is Cross-Site Scripting?
Cross-Site Scripting occurs when an application does not properly validate user input and allows unauthorized code injection. This can happen in various forms, such as:

1. Stored XSS:
In this type of attack, the malicious script is permanently stored on the Target server. When a user visits the affected page, the script is executed, leading to potential data theft or unauthorized actions.

2. Reflected XSS:
Reflected XSS attacks occur when the injected script is embedded in a URL link or form input that is immediately returned to the user. When clicked or submitted, the script executes within the user’s browser, allowing attackers to steal sensitive information.

3. DOM-based XSS:
DOM-based XSS exploits vulnerabilities in JavaScript Document Object Model (DOM) manipulations. The attack occurs when client-side scripts modify the DOM using untrusted data without proper sanitization, leading to script execution within the victim’s browser.

Preventing Cross-Site Scripting Attacks

To protect your web applications from Cross-Site Scripting attacks, follow these best practices:

1. Input Validation and Output Encoding

Always validate and sanitize user input on both client-side and server-side. Apply strict filters to ensure only expected data formats are accepted. Additionally, use output encoding techniques like HTML entity encoding or context-specific escaping when displaying user-generated content.

2. Content Security Policy (CSP)

Implement a Content Security Policy (CSP) header that instructs browsers which resources can be loaded on your website. By defining allowed sources for scripts, stylesheets, and other resources, you can limit the potential damage caused by XSS attacks.

3. Use Web Application Firewalls (WAF)

Deploy a Web Application Firewall that can detect and prevent XSS attacks. WAFs analyze incoming requests and responses to identify and block malicious code injection attempts.

4. Stay Up-to-Date

Regularly update your web application’s software components, including frameworks, plugins, and libraries. Outdated software often contains known vulnerabilities that attackers can exploit.


Cross-Site Scripting poses a significant threat to web applications and user data. Understanding the different types of XSS attacks and implementing appropriate prevention measures is crucial for ensuring the security of your websites.

Remember to validate user input, encode output properly, implement Content Security Policies, consider using Web Application Firewalls, and stay up-to-date with security patches. By following these guidelines, you can significantly reduce the risk of XSS vulnerabilities in your applications.

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