Fixing the Matomo opt-out iframe when using secure headers

Last year, I wrote a blog post about how to secure your website with server headers. When changing the security headers, there is always the chance that some things stop working, as they need “more unsecure” settings. One of these example is the Matomo opt-out iframe and in this blog post I want to show you how to solve it.

The opt-out gets blocked by the browser

If you use Matomo to track your visitors and collect statistics on how they use your site, it’s best to always use the most privacy-friendly settings. You should run the tracking without cookies and also enable the “Do Not Track” option. But even with these settings, you should allow your visitors to opt-out from tracking. To do this, you can create an iframe in the privacy settings of Matomo. This iframe is usually added to your privacy page. If you do this with secure headers set for Matomo, you might get the following error message in browsers:

Refused to display ‘https://matomo.example.com/’ in a frame because it set ‘X-Frame-Options’ to ‘sameorigin’.

This happens when the security headers are too tight not allowing a website with a different domain to embed them.

Allow external domains

One thing you could do now is changing the value of the X-Frame-Options to something more insecure. But we don’t really want that. Instead, you can explicitly allow some domains to embed the iframe. This can be done using the Content-Security-Policy header:

Apache

Header set Content-Security-Policy "frame-ancestors 'self' https://example.com/ https://www.example.com/"

nginx

add_header Content-Security-Policy "frame-ancestors 'self' https://example.com/ https://www.example.com/"

You might already have a Content-Security-Policy set in your server headers. In this case, you can also add these options to the existing header. If you don’t know how to combine different options, the generator from Report UI may be you with this.

Conclusion

Securing a website is very important. But sometimes a higher level of security can interfere with other things. Always make sure to test all things after changing something on the server headers. If visitors are unable to opt-out from tracking, you might have solved a potential security issue, but now you have a privacy issue.

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