Adding Security Headers In Netlify

I normally like my last blog post of the year to end with a year in review. In light of being in Tier 4 local restrictions, there isn't much to do during the festive period unlike previous years. So I have decided to use this time to tinker around with various tech-stacks and work my own site to keep me busy.

Whilst making some efficiency improvements under-the-hood to optimise my sites build and loading times, I randomly decided to check the security headers on and to my surprise received a grade 'D'. When my site previously ran on the .NET Framework, I managed to secure things down to get graded an 'A'. I guess one of my misconceptions on moving to a statically-generated site is there isn't a need. How wrong I was.

A post by Matt Nield explains why static sites need basic security headers in place:

As you add external services for customer reviews, contact forms, and eCommerce integration etc., we increase the number of possible vulnerabilities of the application. It may be true that your core data is on accessed when you rebuild your application, but all of those other features added can leave you, your customers, and your organisation exposed. Being frank, even if you don't add external services there is a risk. This risk is easily reduced using some basic security headers.

Setting security headers on a Netlify hosted site couldn't be simpler. If like me, your site is built using GatsbyJS, you simply need to add a _headers file in the /static directory containing the following header rules:

X-Frame-Options: DENY
X-XSS-Protection: 1; mode=block
Referrer-Policy: no-referrer
X-Content-Type-Options: nosniff
Content-Security-Policy: base-uri 'self'; default-src 'self' https: ; script-src 'self' 'unsafe-inline' https: ; style-src 'self' 'unsafe-inline' https: blob: ; object-src 'none'; form-action 'self' https://*; font-src 'self' data: https: ; connect-src 'self' https: ; img-src 'self' data: https: ;
Feature-Policy: geolocation 'self'; midi 'self'; sync-xhr 'self'; microphone 'self'; camera 'self'; magnetometer 'self'; gyroscope 'self'; fullscreen 'self'; payment 'self'

When adding a "Content-Security-Policy" header be sure to thoroughly re-check your site as you may need to whitelist resources that are loaded from a different origin. For example, I had to make some tweaks specifically to the "Content-Security-Policy" to allow embedded Tweets to render correctly.

My site is now back to its 'A' grade glory!

Useful Links

Check Your Website Headers People!

A website can tell the public a lot about you, from the things you want people to see and other things you probably would not. HTTP Headers can divulge things about your website that you wouldn't necessarily want to make public and its up to the individual to make a decision on what headers they're willing to expose. But what I would recommend is to at least analyse any site prior to moving to a production environment.

Why all of a sudden am I talking about questioning your website HTTP Headers?

It was only by chance when perusing StackOverflow I came across a question about securing HTTP headers, I was directed to a site called I immediately entered this very site for scanning, thinking it would fare quite well. But boy oh boy was I wrong!:

Security Headers (Before)

Based on this result, does this make my website vulnerable? To a certain extent yes. By default you're exposing some key information to potential hackers about how your website is built. For example, here is a simple list of HTTP Headers that could be returned from the server:

  • Web server
  • Framework version
  • Cache handling
  • Cross-site scripting access
  • Referrer policies

Now based on that list alone, what HTTP headers would you hide? From having my eyes opened by the report generated by, as a minimum I would hide anything that shows what technology, framework and server platform I am using. If there happens to be an exploit on the very server or technology you are using, we don't want the whole world to know that especially if you happen to be hosting a high traffic website.

I decided to correct all the issues highlighted by and spent additional time obfuscating some additional headers. Now I can proudly say I've passed. There is just one blemish against the report to do with the "Content-Security-Policy" header, which defines approved sources of content that the browser may load.

Security Headers (After)

I been tweaking around with the rules for this header and I'll be honest when I say it shafted the administration dashboard of my the content management system I use for my site - Kentico CMS. So before I reinstate the header, I need a little more time tweaking.

Another great site to use to analyse the security of your site (.NET sites only) is ASafaWeb, which scans for common configuration vulnerabilities.

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