Angular: how to set up Content-Security-Policy & Trusted Types?

Question

Angular: how to set up Content-Security-Policy & Trusted Types?

2.4k Views Asked by fservantdev At 05 April 2025 at 18:55

Having read the Angular security guidelines, I would like to:

configure the content security policy
enable the trusted types enforcement

Here is how I changed my index.html so far:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta http-equiv="Content-Security-Policy" content="default-src 'self'; style-src 'self' 'unsafe-inline';" />
    <meta http-equiv="Content-Security-Policy" content="trusted-types angular angular#unsafe-bypass; require-trusted-types-for 'script';" />

Right now, I have got a lot of errors in my console:

This document requires 'TrustedScript' assignment.
FooService EvalError: Refused to evaluate a string as JavaScript because this document requires 'Trusted Type' assignment.

My questions:

Is it OK to define the Content-Security-Policy twice/for the both:
One for the "classic" CSP configuration, one for the trusted types?
Does it make sense?
How do they relate with each other?
How do I make it work both locally and in production?
- I understood that this configuration should probably be activated only in production environments (because of JIT),
  using a specific index.production.html file (see).
  I am not a big fan of duplicating the index.html just for two meta properties...
- I also saw that I could use the headers property in my architect.serve.configurations.production,
  but I am not sure if it is better and/or equivalent
Should I even use the trusted-types?
It is recommended by the Angular security guidelines, but still experimental

I read some interesting resources, but they do not show how to concretely use the CSP attribute.
I am using Angular 13.

Original Q&A

There are 2 best solutions below

**Andrey K.** · Answer 1

Just add "safevalues": "^0.1.8" to dependencies and "@types/trusted-types": "^2.0.2" to devDependencies and use it in your code like this:

    import {unwrapHtmlForSink} from 'safevalues';
    import {createHtml} from 'safevalues/implementation/html_impl';
    ...
    this.r.setProperty(this.inputValue.nativeElement, 'innerHTML', unwrapHtmlForSink(createHtml('some_html')));

**Halvor Sakshaug** · Answer 2

You can have multiple CSPs. All of them will be checked separately and your content need to pass all policies. You can have one intended for CSP level 2 and one for CSP level 3 (where level 2 browsers will ignore directives it doesn't understand).

I would recommend setting CSP as a response header. It is simpler to configure per environment and more features are available such as report-uri and frame-ancestors.

Trusted types adds another layer of security and I would implement it if possible after mastering the basic CSP.

Angular: how to set up Content-Security-Policy & Trusted Types?

There are 2 best solutions below

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