139

So, in about 1 hour my extensions failed hard.

I was doing my extension and it was doing what I pretended. I made some changes, and as I didnt liked I deleted them, and now my extension is throwing error:

Refused to apply inline style because it violates the following Content Security Policy directive: "default-src 'self'". Note that 'style-src' was not explicitly set, so 'default-src' is used as a fallback.

What causes this error?

I made my changes in:

popup.html

<!DOCTYPE html>
<html ng-app="PinIt" ng-csp>

<head>
  <link rel="stylesheet" href="css/popup.css">
  <script src="js/lib/jquery-1.8.2.min.js"></script>
  <script src="js/lib/angular.min.js"></script>
  <script src="js/app/app.js"></script>
  <script src="js/app/popup.js"></script>
</head>

<body id="popup">
  <header>
    <h1>PinIt</h1>
  </header>
  <div ng-controller="PageController">
    <div>{{message}}</div>
    <h2>Page:</h2>
    <div id="elem">{{title}}</div>
    <div>{{url}}</div>
    <h2>Imagens:</h2>
    <ul>
      <li ng-repeat="pageInfo in pageInfos" style="list-style: none">
        <div class="imgplusshare">
          <img src={{pageInfo}} class="imagemPopup" />
          <ul class="imas">
            <li id="liFacebook" ng-click="fbshare(pageInfo)">
              <span>
                <img src="facebook_16.png"/>Facebook
              </span>
            </li>
            <li id="liTwitter" ng-click="twshare(pageInfo)">
              <span>
                <img src="twitter-bird-16x16.png"/>Twitter
              </span>
            </li>
            <li id="liGooglePlus" ng-click="gpshare(pageInfo)">
              <span><img src="gplus-16.png"/>Google+</span>
            </li>
            <li id="liEmail" ng-click="mailshare(pageInfo)">
              <span><img src="mail_icon_16.png"/>Email</span>
            </li>
            <hr>
          </ul>

        </div>
      </li>

    </ul>
  </div>
</body>

</html>

popup.js

myApp.service('pageInfoService', function() {
  this.getInfo = function(callback) {
    var model = {};

    chrome.tabs.query({
        'active': true
      },
      function(tabs) {
        if (tabs.length > 0) {
          model.title = tabs[0].title;
          model.url = tabs[0].url;

          chrome.tabs.sendMessage(tabs[0].id, {
            'action': 'PageInfo'
          }, function(response) {

            model.pageInfos = response;

            callback(model);
          });

        }

      });
  };
});
myApp.controller("PageController", function($scope, pageInfoService) {

  pageInfoService.getInfo(function(info) {
    $scope.title = info.title;
    $scope.url = info.url;
    $scope.pageInfos = info.pageInfos;
    $scope.fbshare = function($src) {
      chrome.windows.create({
        url: "http://www.facebook.com/sharer/sharer.php?u=" + $src
      });
    };
    $scope.twshare = function($src) {
      chrome.windows.create({
        url: "https://twitter.com/intent/tweet?url=" + $src
      });
    };
    $scope.gpshare = function($src) {
      chrome.windows.create({
        url: "https://plus.google.com/share?url=" + $src
      });
    };
    $scope.mailshare = function($src) {
      chrome.windows.create({
        url: "mailto:?subject=Imagem Partilhada por PinIt&body=<img src=\"" + $src + "\"\\\>"
      });
    };



    $scope.$apply();


  });
});

Here is my manifest file:

{
  "name": "PinIt",
  "version": "1.0",
  "manifest_version": 2,

  "description": "Pin It",
  "icons": {
    "128": "icon128.png"
  },
  "browser_action": {
    "default_icon": "img/defaultIcon19x19.png",
    "default_popup": "popup.html",
    "default_title": "PinIt"
  },
  "content_scripts": [{
    "js": ["js/lib/jquery-1.8.2.min.js", "js/app/content.js", "js/jquery-ui-1.10.3.custom.js"],
    "matches": ["*://*/*"],
    "run_at": "document_start"
  }],
  "minimum_chrome_version": "18",
  "permissions": ["http://*/*", "https://*/*", "unlimitedStorage", "contextMenus", "cookies", "tabs", "notifications"],
  "content_security_policy": "default-src 'self'"
}

Any suggestion?

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1

8 Answers 8

Reset to default
147

You can also relax your CSP for styles by adding style-src 'self' 'unsafe-inline';

"content_security_policy": "default-src 'self' style-src 'self' 'unsafe-inline';"

This will allow you to keep using inline style in your extension.

Important note

As others have pointed out, this is not recommended, and you should put all your CSS in a dedicated file. See the OWASP explanation on why CSS can be a vector for attacks (kudos to @ KayakinKoder for the link).

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10
29

As the error message says, you have an inline style, which CSP prohibits. I see at least one (list-style: none) in your HTML. Put that style in your CSS file instead.

To explain further, Content Security Policy does not allow inline CSS because it could be dangerous. From An Introduction to Content Security Policy:

"If an attacker can inject a script tag that directly contains some malicious payload .. the browser has no mechanism by which to distinguish it from a legitimate inline script tag. CSP solves this problem by banning inline script entirely: it’s the only way to be sure."

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8
  • 23
    This doesn't make any sense to me. For inline scripts I understand it, but this question is about inline styles. Is it possible to inject a malicious inline style?
    – Andrew Schulman
    Commented Jan 29, 2016 at 16:47
  • 7
    This was the first result for the search [malicious inline style]: dontkry.com/posts/code/disable-inline-styles.html
    – sowbug
    Commented Feb 1, 2016 at 4:23
  • 3
    The argument on that page seems invalid. It uses examples of non-inline styles to demonstrate why you might want to block inline styles. The examples it gives are indeed evil things you could do with CSS, but why would you block only inline styles, instead of, for instance, all CSS?
    – Hakanai
    Commented Jun 17, 2016 at 2:24
  • 4
    @Trejkaz the styles mentioned on the dontkry page are inline styles. In this context, "inline" includes <style> elements, not just style= attributes; non-inline means putting a link rel="Stylesheet" element in the head. The point is it's is a belt-and-braces protection against XSS, and we assume the XSS attacker can add anything to the page's body but cannot add a link rel="Stylesheet" to the head.
    – Silas S. Brown
    Commented Mar 6, 2017 at 10:18
  • 2
    Because someone can add any text to your site with css. Think: ":after{content:"You are hacked", fontSize:666}
    – Ali Mert Çakar
    Commented Sep 13, 2020 at 22:17
13

As per http://content-security-policy.com/ The best place to start:

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

Never inline styles or scripts as it undermines the purpose of CSP. You can use a stylesheet to set a style property and then use a function in a .js file to change the style property (if need be).

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6

Well, I think it is too late and many others have the solution so far.

But I hope this can Help:

I'm using react for an identity server so 'unsafe-inline' is not an option at all. If you look at your console and actually read the CSP docs, you might find that there are three options for solving the issue:

  1. 'unsafe-inline' as it says is unsafe if your project is using CSPs is for one reason and it is like throwing out the complete policy, will be the same to no have CSP policy at all

    1. 'sha-XXXCODE' this is good, safe but not optimal because there is a lot of manual work and every compilation the SHA might change so it will become easily a nightmare, use only when the script or style is unlikely to change and there are few references

    2. Nonce. This is the winner!

Nonce works in the similar way as scripts

CSP HEADER ///csp stuff nonce-12331

<script nonce="12331">
   //script content
</script>

Because the nonce in the csp is the same that the tag, the script will be executed

In the case of inline styles, the nonce also came in the form of attribute so the same rules apply.

so generate the nonce and put it on your inline scritps

If you are using webpack maybe you are using the style-loader

the following code will do the trick


module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [
          {
            loader: 'style-loader',
            options: {
              attributes: {
                nonce: '12345678',
              },
            },
          },
          'css-loader',
        ],
      },
    ],
  },
};
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2
  • 16
    No, you shouldn't hard code nonces. These should be generated on the fly for each load, otherwise they are as insecure as not having CSP at all.
    – marcellothearcane
    Commented Sep 23, 2020 at 9:18
  • 8
    suggestions on how to generate a nonce on each load for a static SPA?
    – Kyle Fong
    Commented Feb 20, 2021 at 22:46
5

Another method is to use the CSSOM (CSS Object Model), via the style property on a DOM node.

var myElem = document.querySelector('.my-selector');
myElem.style.color = 'blue';

More details on CSSOM: https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement.style

As mentioned by others, enabling unsafe-line for css is another method to solve this.

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1
  • Also one can use myElem.style.cssText = 'color: blue;'
    – Finesse
    Commented Jan 28, 2022 at 16:22
0

You can use in Content-security-policy add "img-src 'self' data:;" And Use outline CSS.Don't use Inline CSS.It's secure from attackers.

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1
  • 3
    That's already addressed in one of the answers above.
    – Al.G.
    Commented Jul 15, 2020 at 8:21
0

If you have some content where you can't avoid inline css for example REST API response

or user input. then in that case I have created the solution for in the following blog. where you can separate html and css from each other and try to add the nonce value from the html meta tag header(which will be generate at the time of build)

CSP handling for inline css using nonce

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1
  • 2
    While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review
    – Moritz Ringler
    Commented Feb 21, 2023 at 18:44
0

If I may ride this post, since I'm trying some of the solutions that were suggested here. I would highly like to avoid the "unsafe-inline" part, and would prefer using the nonse which i already set for each script tag, like this:

<script nonce="...."></script>.

On my case, I set the csp parameter to have:

style-src 'self' 'nonce-codexyzxyzxyz' https://example.com

The script is included with the nonce="..." part, and yet, the JS file is being blocked from changing the inline style of some div I have. I am trying to understand why? because after all, I told the CSP which nonce code (which the tag has) can "change", and which domain, but still blocks.

How can I make it work in the safe way?. After all, I assume we can add "whitelist" just as I did, but for some reason it does not work.

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