How to Use the Referrer-policy Header to Control Data Leakage Between Sites

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The Referrer-Policy header is a crucial tool for web developers and site administrators who want to control how much referral information is shared between websites. Proper configuration can help prevent data leakage and protect user privacy.

Understanding the Referrer-Policy Header

The Referrer-Policy header dictates what information is sent in the Referer header of HTTP requests. This information can include the URL of the previous page, which might contain sensitive data. By setting an appropriate policy, you can limit this exposure.

Common Referrer-Policy Settings

  • no-referrer: No referrer information is sent with requests.
  • no-referrer-when-downgrade: Default policy; referrer is sent only over HTTPS to HTTPS.
  • origin: Only the origin (domain) is sent as referrer.
  • strict-origin: Only send referrer over HTTPS, and only the origin.
  • same-origin: Send referrer only if the request is to the same origin.
  • origin-when-cross-origin: Send full URL for same-origin requests; only origin for cross-origin.
  • strict-origin-when-cross-origin: Send full URL for same-origin; only origin over HTTPS for cross-origin.

Implementing the Referrer-Policy Header

You can set the Referrer-Policy header in your server configuration, through HTTP headers, or via meta tags in HTML. Here are some common methods:

Server Configuration

For example, in Apache, add the following line to your .htaccess file:

Header set Referrer-Policy "strict-origin-when-cross-origin"

Using Meta Tags

Insert the following in the <head> section of your HTML:

<meta name="referrer" content="strict-origin-when-cross-origin">

Benefits of Proper Referrer-Policy Configuration

Implementing an appropriate Referrer-Policy helps:

  • Protect user privacy by limiting sensitive data sharing.
  • Reduce the risk of leaking internal URLs or parameters.
  • Enhance overall security by controlling data flow between sites.

Conclusion

Using the Referrer-Policy header effectively is a simple yet powerful way to control data leakage between websites. Proper configuration aligns with privacy best practices and strengthens your site’s security posture.