Using HTTP headers to protect your visitor’s security and privacy

Recently there has been a lot of controversy over Google starting to use Federated Learning of Cohorts (FLoC) in its Chrome browser. This new technique is used to track users without using third party cookies, but has severe privacy implications because it actually makes fingerprinting users easier and can reveal your interests to websites.

To prevent tracking by FLoC and other tracking techniques, there is only one good solution: stop using Google Chrome. The best privacy friendly browser is Firefox, especially if you set it to strict enhanced tracking protection. If you really need to use Chrome, then at least install one of the open source extensions which disable FLoC and Privacy Badger for other tracking protection.

As a website owner, you can also do something to protect your users. You can opt out your website to be included in cohort computation by sending the header Permissions-Policy: interest-cohort=()

This can be easily done for all your websites by modifying your Apache configuration. While at it, you should set some other security and privacy related headers, notably:

  • X-Frame-Options "SAMEORIGIN": this makes sure that browsers will not allow your website to be included in an iframe on another domain.
  • X-Content-Type-Options "nosniff": This will prevent the browser from trying to automatically detect the file type of a downloaded file instead of using the MIME type sent by the server. This can mitigate attacks where a hacker manages to upload a malicious file by giving it a filename which makes it look like a harmless file type which is then served to your visitors.
  • Referrer-Policy "no-referrer-when-downgrade": when a visitor clicks on a link, the browser will only send the referrer when it’s not going from a HTTPS to a HTTP connection. This is fine if your URLs don’t contain any private information. If they do, then consider using strict-origin-when-cross-origin, so that only your domain name instead of the complete URL is sent as referrer if people click on a link leading to an external website, or even same-origin, which prevents any referrer being sent to external sites. You should probably do this for an internal website, web application or wiki, webmail, etc. More information about Referrer-Policy

To set these in Apache in Debian, create a file /etc/apache2/conf-available/security-headers.conf with these contents:

<IfModule mod_headers.c>
   Header always set X-Frame-Options "SAMEORIGIN"
   Header always set X-Content-Type-Options "nosniff"
   Header always set Referrer-Policy "no-referrer-when-downgrade"
   Header always set Permissions-Policy: interest-cohort=()
</IfModule>

Then make sure the mod_headers module is loaded and this file is enabled by running these commands:

# a2enmod headers
# a2enconf security-headers
# systemctl reload apache2

Another important header to set in your SSL virtualhosts is the HSTS header: it ensures that the browser will automatically use HTTPS every time when connecting to the website in the future. Place this in your SSL enabled virtualhost:

<IfModule mod_headers.c>
   Header always set Strict-Transport-Security "max-age=63072000"
</IfModule>

Then you should also add this to your non-SSL virtualhost to redirect all visitors using HTTP to HTTPS:

<IfModule mod_rewrite.c>
   RewriteEngine on
   RewriteCond %{HTTPS} !=on
   RewriteRule .* https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]
</IfModule>

Of course make sure mod_rewrite is enabled if that’s not yet the case:

# a2enmod rewrite
# systemctl reload apache2

You can check your server configuration on securityheaders.com. There you can also find more information about the headers Cross-Origin-Embedder-Policy, Cross-Origin-Opener-Policy and Cross-Origin-Resource-Policy, some other security related headers. Because they require more changes to your website to implement correctly, I’m not discussing them here.

More information

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