How to check for XSS?

This blog will help you check for cross site scripting (XSS).

Dec 5, 2024

How to Test for Cross-Site Scripting (XSS)

Cross-Site Scripting (XSS) is a security vulnerability that allows an attacker to inject malicious scripts into content from otherwise trusted websites. Here, we will discuss how to test for XSS vulnerabilities.

What is XSS?

XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser-side script, to a different end user. There are three main types of XSS attacks:

  1. Stored XSS: The malicious script is stored on the target server.
  2. Reflected XSS: The malicious script is reflected off a web server.
  3. DOM-based XSS: The vulnerability exists in client-side code rather than server-side code.

Testing for XSS

1. Manual Testing

To manually test for XSS, you can try injecting common XSS payloads into input fields and see if they get executed. Here are some common payloads:

<script>alert('XSS')</script>
<img src=x onerror=alert('XSS')>

2. Automated Testing

There are several tools available to automate XSS testing:

  • OWASP ZAP: An open-source web application security scanner.
  • Burp Suite: A graphical tool for testing web application security.

Example

Let’s consider a simple example where a web application displays user input without proper sanitization:

<!DOCTYPE html>
<html>
<head>
    <title>XSS Test</title>
</head>
<body>
    <form method="GET">
        <input type="text" name="input" />
        <input type="submit" value="Submit" />
    </form>
    <div>
        You entered: <?php echo $_GET['input']; ?>
    </div>
</body>
</html>

If you enter <script>alert('XSS')</script> in the input field and submit the form, the script will execute, indicating an XSS vulnerability.

Preventing XSS

To prevent XSS, always sanitize and escape user input. Here are some tips:

  • Use proper escaping for HTML, JavaScript, and CSS.
  • Use security libraries and frameworks that provide built-in XSS protection.
  • Validate input on both the client and server sides.

Conclusion

Testing for XSS is crucial for web application security. By understanding the different types of XSS and using both manual and automated testing methods, you can identify and mitigate these vulnerabilities.