HTTPS Embedding Security: Prevent Data Theft

TL;DR

An attacker can steal information from your HTTPS page if they embed it in a malicious website using an <iframe> or similar technique. This is because the browser still loads your content, even within another site. The key to preventing this is using Content Security Policy (CSP) and Frame Ancestors headers on your server.

How Embedding Works & Why It’s a Risk

Imagine you have a secure banking page (https://yourbank.com). An attacker creates a fake website (http://evil.example.com) and embeds your banking page within it using an <iframe> tag:

<iframe src="https://yourbank.com" width="800" height="600"></iframe>

Users visiting http://evil.example.com will see your banking page loaded inside the attacker’s site. They might think they are on your legitimate website, and enter their login details – which are then sent to the attacker.

Steps to Protect Your HTTPS Page

1. Understand Content Security Policy (CSP)
• CSP is a security standard that tells the browser where it’s allowed to load resources from. It helps prevent cross-site scripting (XSS) and embedding attacks.
• You configure CSP using HTTP headers sent by your server.
2. Implement Frame Ancestors Header
• The Frame-Ancestors header specifically controls which domains are allowed to embed your page in an <iframe>.
• To allow only your own domain, set the header like this:

Header always set X-Frame-Options "SAMEORIGIN"

• This tells the browser to only allow embedding from pages on the same origin (domain, protocol and port).
• If you need to allow specific other domains:

Header always set X-Frame-Ancestors "yourbank.com anotherdomain.com"

• Important: Be very careful about which domains you allow! Only include trusted sites.
3. Configure CSP for your web server
• The exact method depends on your web server (Apache, Nginx, etc.). Here are some examples:
• Apache (.htaccess file): Add the following line to your .htaccess file:

Header always set Content-Security-Policy "frame-ancestors 'self' yourbank.com;"

• Nginx (configuration file): Add the following to your server block configuration:

add_header Content-Security-Policy "frame-ancestors 'self' yourbank.com;";

• Replace yourbank.com with your actual domain(s). The `’self’` keyword allows embedding from the same origin.
4. Test Your Configuration
• Use a browser developer tool (usually by pressing F12) to check if the headers are being sent correctly. Look in the ‘Network’ tab and inspect the response headers for your page.
• You can also use online CSP testing tools like CSP Evaluator.
5. Regularly Review Your CSP
• As your website evolves, you might need to update your CSP to reflect changes in allowed domains or resources.

Additional Considerations

• X-Frame-Options vs. Content-Security-Policy: X-Frame-Options is an older header, and CSP is generally preferred as it offers more flexibility and control.
• Subdomains: If you want to allow embedding from subdomains of your domain, you’ll need to include them specifically in the Frame-Ancestors directive (e.g., yourbank.com *.yourbank.com).