What Is Cross-Site Scripting and Forgery?


Angela Bailey

Cross-Site Scripting and Forgery: Understanding the Threats

When it comes to web security, there are several threats that developers and users need to be aware of. Two common types of attacks that can compromise the security of a website are Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF). In this article, we will explore what these threats are, how they work, and what you can do to protect your applications.

Cross-Site Scripting (XSS)

Cross-Site Scripting (XSS) is a vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This attack occurs when user input is not properly sanitized or validated before being displayed on a website. The injected scripts can then execute in the victim’s browser, leading to various consequences such as stealing sensitive information or even taking control of the user’s account.

Types of XSS Attacks:

  • Stored XSS: This type of attack occurs when the malicious script is permanently stored on a website’s server. When a user visits the compromised page, the script is served from the server and executed in their browser.
  • Reflected XSS: In this case, the injected script is part of the URL itself or included in a form input.

    When the user clicks on a specially crafted link or submits a form, the script gets executed.

  • DOM-based XSS: This variant takes advantage of vulnerabilities in client-side JavaScript code. The malicious script directly manipulates the Document Object Model (DOM) of a webpage, leading to unexpected behavior.

Preventing XSS Attacks:

To protect your application from XSS attacks, it is crucial to follow best practices such as:

  • Input Validation: Always validate and sanitize user input before displaying it on a web page. Use proper output encoding techniques to prevent script execution.
  • Content Security Policy (CSP): Implement a Content Security Policy that restricts the types of content that a browser can load on your website. This helps mitigate the impact of XSS attacks.
  • HTTP-only Cookies: Set the ‘HttpOnly’ flag on session cookies to prevent client-side scripts from accessing them.

Cross-Site Request Forgery (CSRF)

Cross-Site Request Forgery (CSRF) is an attack that tricks authenticated users into unknowingly executing unwanted actions on a website. Unlike XSS, CSRF attacks do not Target vulnerabilities in the website’s code but exploit the trust between a user and the website they are authenticated with.

How CSRF Attacks Work:

An attacker crafts a malicious webpage or sends an email containing a link that, when clicked by the victim, triggers unwanted actions on another website where the victim is authenticated. Since the request originates from the victim’s browser, it includes their session cookies, making it appear legitimate to the Target website.

Mitigating CSRF Attacks:

To protect your application against CSRF attacks, you can implement these countermeasures:

  • CSRF Tokens: Include unique tokens in each request that modify server-side state. These tokens should be generated per session and validated before processing requests.
  • Samesite Attribute: Set the ‘SameSite’ attribute on cookies to restrict their usage to same-site requests only.

    This prevents cookies from being sent in cross-origin requests.

  • Double-Submit Cookie: Use a double-submit cookie pattern where a cookie value is included both in a request header and as a request parameter. The server then compares the values to validate the request.


Being aware of the risks posed by Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF) is crucial for developers and users alike. By understanding how these attacks work and implementing appropriate security measures, you can protect your websites and applications from potential threats. Remember to always validate user input, sanitize output, and stay up-to-date with the latest security best practices.

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