Clickjacking Defense: Frame Busting Script

This code snippet demonstrates a JavaScript-based frame busting technique to prevent clickjacking attacks. Clickjacking occurs when an attacker overlays a transparent or opaque layer on top of a legitimate website, tricking users into clicking something different from what they perceive.

Understanding Clickjacking

Clickjacking, also known as UI redress attack, manipulates users into performing actions they didn't intend to. Attackers embed a target page within an <iframe> on a malicious site. By carefully positioning and styling the iframe, they can trick users into clicking buttons or links on the target page while believing they are interacting with the malicious site.

This can lead to unintended consequences such as liking a social media post, changing account settings, or even making purchases without the user's knowledge.

Frame Busting Technique

This snippet checks if the current window (window.self) is the topmost window (window.top). If they are different, it means the page is being displayed within an iframe. In this case, the script redirects the topmost window to the current page's URL, effectively breaking out of the iframe.

if (window.top !== window.self) {
  window.top.location = window.self.location;
}

Explanation of the Code

• window.top: Refers to the topmost browsing context, which is the main window or tab.
• window.self: Refers to the current browsing context, which is the window or iframe in which the code is running.
• window.top.location = window.self.location: This line performs the redirection. It sets the location (URL) of the topmost window to the location of the current window. This forces the page to load outside of any iframe.

Real-Life Use Case

Imagine a banking website. An attacker could embed the bank's login page in an iframe on a malicious site. When a user tries to log in on the attacker's site, they're unknowingly interacting with the real bank login page. The attacker can then steal their credentials or trick them into transferring funds. Implementing frame busting prevents the bank's page from being embedded in this way.

Best Practices

While frame busting is a common technique, it's not foolproof. Modern browsers offer security headers that provide more robust protection against clickjacking. It's recommended to use Content Security Policy (CSP) and X-Frame-Options headers in addition to or instead of frame busting.

For CSP: Content-Security-Policy: frame-ancestors 'self'; or Content-Security-Policy: frame-ancestors 'none'; to completely prevent framing.

For X-Frame-Options: X-Frame-Options: DENY or X-Frame-Options: SAMEORIGIN

Alternatives

Content Security Policy (CSP) and X-Frame-Options headers are the preferred alternatives. CSP allows fine-grained control over where your site can be framed. X-Frame-Options offers a simpler approach by either denying framing altogether or allowing it only from the same origin.

When to Use Them

Implement clickjacking defenses on any website where user interactions can have significant consequences, such as financial transactions, account settings changes, or sensitive data modification. Any site that requires user authentication should have clickjacking protection.

Interview Tip

When discussing clickjacking defenses, highlight the importance of using both client-side (frame busting) and server-side (CSP, X-Frame-Options) techniques. Explain the limitations of frame busting and the advantages of using security headers. Be prepared to explain the different CSP directives and X-Frame-Options values.

Pros and Cons of Frame Busting

Pros: Simple to implement. Provides a basic level of protection. Cons: Can be bypassed by sophisticated attackers (e.g., by sandboxing the iframe). Not as robust as security headers. Can interfere with legitimate uses of iframes (although this is often undesirable from a security perspective).