How should the nonce be properly set in the csp policy?

I've been attempting to incorporate a nonce into the csp policy but it's not functioning as anticipated.

Here's the code snippet I'm currently using for testing purposes:

server.js

  express.use(function(req, res, next) {
    res.set({
      "Content-Security-Policy":"script-src 'self' 'nonce-random1'"
    });
    return next();
  });

index.html

  <script nonce="random1" type="text/javascript" src="/script1.js"> 
  </script>

When checking the browser console, I encountered this error message: Refused to execute inline event handler because it violates the following Content Security Policy directive: "script-src 'self' 'nonce-random1'...

As an experiment, I attempted to add the source /script1.js as if it were a domain:

  express.use(function(req, res, next) {
    res.set({
      "Content-Security-Policy":"script-src 'self' /script1.js"
    });
    return next();
  });

Despite my efforts, the solution didn't work and I still received the same error message.

I checked the documentation and confirmed that the syntax was correct. I also searched for relevant questions or articles but couldn't find any useful information.

I prefer not to use unsafe-inline. Instead, I plan to implement a one-time hash as a nonce for each request in the future.

Does anyone have insight into why the nonce is not functioning as expected?

Answer №1

When it says 'no' to executing an inline event handler

This indicates that you have event handlers embedded in tags like <div onclick='handler()'> or

<body onload='some_javascript_here'>
, etc.
Your
<script nonce='random1'>...</script>
is being executed, which can be confirmed by adding console.log('I am done').

Replace inline event handlers with addEventListener() or utilize jQuery if feasible.

"Content-Security-Policy":"script-src 'self' /script1.js"

is deemed incorrect; relative URLs like /script1.js are not permitted in the directive.
Your initial CSP setting

"Content-Security-Policy":"script-src 'self' 'nonce-random1'"
is accurate.

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