What Is Cross-Site Scripting With Example?


Scott Campbell

What Is Cross-Site Scripting With Example?

Cross-Site Scripting, commonly known as XSS, is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This occurs when a web application does not properly validate user input and fails to sanitize it before displaying it back to the user.

Types of Cross-Site Scripting:

There are three main types of XSS attacks:

1. Stored XSS: Also known as persistent XSS, this type of attack involves injecting malicious code that is permanently stored on the Target server. When other users access the affected page, the injected script executes in their browsers, potentially leading to unauthorized data disclosure or even control over their accounts.

2. Reflected XSS: Reflected XSS occurs when the injected script is embedded in a URL or other input that is immediately returned by the server. The script is then executed in the victim’s browser when they click on a manipulated link or visit a specially crafted website.

3. DOM-based XSS: Unlike stored and reflected XSS, DOM-based XSS does not rely on server-side vulnerabilities.

Instead, it exploits flaws in client-side JavaScript code that dynamically modifies the Document Object Model (DOM) of a web page. Attackers manipulate the DOM to execute malicious scripts in victims’ browsers.


Let’s consider an example to better understand how cross-site scripting works:

Suppose there is a blog website where users can post comments on articles. The website displays these comments without proper validation and sanitation.

An attacker takes advantage of this vulnerability by posting a comment containing an embedded script:



When another user visits the article with this malicious comment, their browser will execute the injected script and display an alert box with the message ‘XSS attack successful!’. This demonstrates how an attacker can exploit a cross-site scripting vulnerability to execute arbitrary code in the victim’s browser.

Preventing Cross-Site Scripting:

To protect web applications from XSS attacks, it is crucial to implement proper input validation and output encoding. Here are some preventive measures:

1. Input Validation: Validate and sanitize all user input, both on the client-side and server-side. Use appropriate libraries or frameworks that have built-in security features to prevent code injection. Output Encoding: Encode user-generated content before displaying it back to other users. This ensures that any injected scripts are treated as plain text rather than executable code. Content Security Policy (CSP): Implement a Content Security Policy that restricts the execution of scripts from external sources and limits the allowed sources for other types of content.

4. Avoiding Inline Scripts: Minimize or eliminate the use of inline scripts in your web application. Instead, use external JavaScript files with proper sanitization.

5. Regular Security Audits: Regularly audit your web application’s codebase for potential security vulnerabilities, including XSS vulnerabilities.


Cross-Site Scripting (XSS) is a severe security vulnerability that can have significant consequences for both website owners and users. By understanding the different types of XSS attacks and implementing preventive measures, developers can protect their applications from this common threat.

Remember to always validate user input, encode output, and stay updated with best practices for web application security to minimize the risk of cross-site scripting attacks.

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