Managing the ‘Content Security Policy’ of your site


The ‘Content Security Policy’ response header is used to enhance a website’s security. It allows control of how resources are loaded, whitelisting trusted domains.

Any security audit will highlight this as a key recommendation.

Content-Security-Policy: default-src 'self' ; script-src; img-src; connect-src;

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Content Security Policy is an extra layer of security that protects against certain types of attack vectors (XSS, Click Jacking), anything you can do to protect the end-user is beneficial.

It is common practice these days for developers to draw in 3rd party packages to deliver a feature and these packages will also draw in other packages. This means that malicious code can get drawn into your solution without your knowledge.

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It is possible to be very granular when configuring the security policy. This gives you a high level of control of what can be loaded and where data can be sent.

Although the Content Security Policy can be added at a meta tag, it is typically delivered in a response header, additionally, it is also possible to enable specific inline scripts by adding a nonce value.

Testing your policy

Changes to the policy can inadvertently disable features on your site. YouTube videos can fail to load, analytics stops sending data, javascript components can fail. To help mitigate this you should either make any changes as ‘report only’ and monitor the output or configure the policy to report issues. This means that any issues are either reported within the browser console or are sent to a 3rd party reporting service.


You have deployed your policy, it’s been tested and signed off, but then things start to fail. Unfortunately, things do change, a dependency can update the endpoints they use or more typically a new tool is added via Google Tag Manager.

Managing the content security policy can be challenging. A common approach is to create a Url Rewrite outbound rule. This means that when the policy needs to change you have to update your source code and redeploy your site, not very efficient.

Is there an easier way?

Read my next post where I will introduce the new Episerver / Optimizely module that simplifies the management of the Content Security Policy.

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