Make Angular working with restrictive Content Security Policy (CSP)

Question

I cannot make base Angular2 (final) application works with the following restrictive CSP.

default-src 'none'; script-src 'self'; style-src 'self'; font-src 'self'; img-src 'self' data:; connect-src 'self' 

There are one unsafe-eval error in lang.js and two in zone.js. Could you provide a solution ?

Step to reproduce with Angular CLI

I have created a GitHub repository. You can also follow the instructions below.

Use the last Angular CLI with Webpack 6.0.8 and the new application created with the instructions below.

ng new csp-test 

Insert in the index.html the meta tag defining the following restrictive Content Security Policy.

<meta    http-equiv="Content-Security-Policy"    content="default-src 'none';script-src 'self';style-src 'self';font-src 'self';img-src 'self' data:;connect-src 'self'"> 

Then serve the application.

ng serve 

Access http://localhost:4200/, the page does not load since scripts are blocked by CSP.

Errors

lang.js

lang.js:335 Uncaught EvalError: Refused to evaluate a string as JavaScript because 'unsafe-eval' is not an allowed source of script in the following Content Security Policy directive: "script-src 'self'". 

with the source code.

335: return new (Function.bind.apply(Function, [void 0].concat(fnArgNames.concat(fnBody))))().apply(void 0, fnArgValues); 

zone.js

zone.js:344 Unhandled Promise rejection: Refused to evaluate a string as JavaScript because 'unsafe-eval' is not an allowed source of script in the following Content Security Policy directive: "script-src 'self'".  ; Zone: <root> ; Task: Promise.then ; Value: EvalError: Refused to evaluate a string as JavaScript because 'unsafe-eval' is not an allowed source of script in the following Content Security Policy directive: "script-src 'self'".  zone.js:346 Error: Uncaught (in promise): EvalError: Refused to evaluate a string as JavaScript because 'unsafe-eval' is not an allowed source of script in the following Content Security Policy directive: "script-src 'self'".(…) 

with the source code.

343: if (rejection) { 344:     console.error('Unhandled Promise rejection:', rejection instanceof Error ? rejection.message : rejection, '; Zone:', e.zone.name, '; Task:', e.task && e.task.source, '; Value:', rejection, rejection instanceof Error ? rejection.stack : undefined); 345: } 346: console.error(e); 

Answer 1

Edited answer for @angular/cli>=8.2

From this Github thread, one can use the index property in angular.json to control the generation of the application's HTML index:

build: {   ...   "configurations": {     "production": {       "index": {         "input": "src/index.production.html",          "output": "index.html"        },       ...     }   } } 

Original answer

I've found a way to have restrictive CSP on my production environment while still being able to use the JTI compliler for development.

• Add a second file: index.production.html to the src folder.
• Copy the contents of index.html to that file, and add the restrictive CSP header.

<meta http-equiv="Content-Security-Policy"  content="default-src 'none';   frame-src 'self';   script-src 'self';   style-src 'self' 'unsafe-inline';   font-src 'self';   img-src 'self' data:;   connect-src 'self'"> 

• Then, add to your angular.json the following:

build: {   ...   "configurations": {     "production": {       "fileReplacements": [         {           "replace": "src/index.html",           "with": "src/index.production.html"         }       ],       ...     }   } } 

This makes sure that when you run a production build, it will use the index.production.html with the restrictive CSP, and when you're running it locally, you can use the JTI compiler.

Answer 2

Using ahead-of-time compilation solves the problem. The following command can be used to build an application working with restrictive CSP.

ng build --prod 

To test it locally you can use

ng serve --prod