@melloware/csp-webpack-plugin

CSP Webpack Plugin

About

This plugin was forked from the wonderful work done by Slack but adds some key features:

• Generate SHA hashes for external and internal JS files
• Configure NONCE for pre-loaded scripts
• Special handling for PrimeReact inline CSS styles
• Typescript definition

Description

This plugin will generate meta content for your Content Security Policy tag and input the correct data into your HTML template, generated by html-webpack-plugin.

All inline JS and CSS will be hashed and inserted into the policy.

Installation

Install the plugin with npm:

npm i --save-dev @melloware/csp-webpack-plugin

Basic Usage

Include the following in your webpack config:

const HtmlWebpackPlugin = require('html-webpack-plugin');
const CspHtmlWebpackPlugin = require('@melloware/csp-webpack-plugin');

module.exports = {
  // rest of webpack config

  plugins: [
    new HtmlWebpackPlugin()
    new CspHtmlWebpackPlugin({
      // config here, see below
    })
  ]
}

Recommended Configuration

By default, the @melloware/csp-webpack-plugin has a very lax policy. You should configure it for your needs.

A good starting policy would be the following:

new CspHtmlWebpackPlugin({
  'script-src': '',
  'style-src': ''
});

Although we're configuring script-src and style-src to be blank, the CSP plugin will scan your HTML generated in html-webpack-plugin for external/inline script and style tags, and will add the appropriate hashes and nonces to your CSP policy. This configuration will also add a base-uri and object-src entry that exist in the default policy:

<meta http-equiv="Content-Security-Policy" content="
  base-uri 'self';
  object-src 'none';
  script-src 'sha256-0Tumwf1AbPDHZO4kdvXUd4c5PiHwt55hre+RDxj9O3Q='
             'nonce-hOlyTAhW5QI5p+rv9VUPZg==';
  style-src 'sha256-zfLUTOi9wwJktpDIoBZQecK4DNIVxW8Tl0cadROvQgo='
">

This configuration should work for most use cases, and will provide a strong layer of extra security.

All Configuration Options

CspHtmlWebpackPlugin

This CspHtmlWebpackPlugin accepts 2 params with the following structure:

• {object} Policy (optional) - a flat object which defines your CSP policy. Valid keys and values can be found on the MDN CSP page. Values can either be a string, or an array of strings.
• {object} Additional Options (optional) - a flat object with the optional configuration options:
  • {boolean|Function} enabled - if false, or the function returns false, the empty CSP tag will be stripped from the html output.
    • The htmlPluginData is passed into the function as it's first param.
    • If enabled is set the false, it will disable generating a CSP for all instances of HtmlWebpackPlugin in your webpack config.
  • {string} hashingMethod - accepts 'sha256', 'sha384', 'sha512' - your node version must also accept this hashing method.
  • {object} hashEnabled - a <string, boolean> entry for which policy rules are allowed to include hashes
  • {object} nonceEnabled - a <string, boolean> entry for which policy rules are allowed to include nonces
  • {Function} processFn - allows the developer to overwrite the default method of what happens to the CSP after it has been created
    • Parameters are:
      • builtPolicy: a string containing the completed policy;
      • htmlPluginData: the HtmlWebpackPlugin object;
      • $: the cheerio object of the html file currently being processed
      • compilation: Internal webpack object to manipulate the build

HtmlWebpackPlugin

The plugin also adds a new config option onto each HtmlWebpackPlugin instance:

• {object} cspPlugin - an object containing the following properties:
  • {boolean} enabled - if false, the CSP tag will be removed from the HTML which this HtmlWebpackPlugin instance is generating.
  • {object} policy - A custom policy which should be applied only to this instance of the HtmlWebpackPlugin
  • {object} hashEnabled - a <string, boolean> entry for which policy rules are allowed to include hashes
  • {object} nonceEnabled - a <string, boolean> entry for which policy rules are allowed to include nonces
  • {Function} processFn - allows the developer to overwrite the default method of what happens to the CSP after it has been created
    • Parameters are:
      • builtPolicy: a string containing the completed policy;
      • htmlPluginData: the HtmlWebpackPlugin object;
      • $: the cheerio object of the html file currently being processed
      • compilation: Internal webpack object to manipulate the build

Order of Precedence:

You don't have to include the same policy / hashEnabled / nonceEnabled configuration object in both HtmlWebpackPlugin and CspHtmlWebpackPlugin.

• Config included in CspHtmlWebpackPlugin will be applied to all instances of HtmlWebpackPlugin.
• Config included in a single HtmlWebpackPlugin instantiation will only be applied to that instance.

In the case where a config object is defined in multiple places, it will be merged in the order defined below, with former keys overriding latter. This means entries for a specific rule will not be merged; they will be replaced.

> HtmlWebpackPlugin cspPlugin.policy
> CspHtmlWebpackPlugin policy
> CspHtmlWebpackPlugin defaultPolicy

Appendix

Default Policy:

{
  'base-uri': "'self'",
  'object-src': "'none'",
  'script-src': ["'unsafe-inline'", "'self'", "'unsafe-eval'"],
  'style-src': ["'unsafe-inline'", "'self'", "'unsafe-eval'"]
};

Default Additional Options:

{
  enabled: true
  hashingMethod: 'sha256',
  hashEnabled: {
    'script-src': true,
    'style-src': true
  },
  nonceEnabled: {
    'script-src': true,
    'style-src': true
  },
  processFn: defaultProcessFn
}

Full Default Configuration:

new HtmlWebpackPlugin({
  cspPlugin: {
    enabled: true,
    policy: {
      'base-uri': "'self'",
      'object-src': "'none'",
      'script-src': ["'unsafe-inline'", "'self'", "'unsafe-eval'"],
      'style-src': ["'unsafe-inline'", "'self'", "'unsafe-eval'"]
    },
    hashEnabled: {
      'script-src': true,
      'style-src': true
    },
    nonceEnabled: {
      'script-src': true,
      'style-src': true
    },
    processFn: defaultProcessFn  // defined in the plugin itself
  }
});

new CspHtmlWebpackPlugin({
  'base-uri': "'self'",
  'object-src': "'none'",
  'script-src': ["'unsafe-inline'", "'self'", "'unsafe-eval'"],
  'style-src': ["'unsafe-inline'", "'self'", "'unsafe-eval'"]
}, {
  enabled: true,
  hashingMethod: 'sha256',
  hashEnabled: {
    'script-src': true,
    'style-src': true
  },
  nonceEnabled: {
    'script-src': true,
    'style-src': true
  },
  processFn: defaultProcessFn  // defined in the plugin itself
})

Advanced Usage

Generating a file containing the CSP directives

Some specific directives require the CSP to be sent to the client via a response header (e.g. report-uri and report-to) You can set your own processFn callback to make this happen.

nginx

In your webpack config:

const RawSource = require('webpack-sources').RawSource;

function generateNginxHeaderFile(
  builtPolicy,
  _htmlPluginData,
  _obj,
  compilation
) {
  const header =
    'add_header Content-Security-Policy "' +
    builtPolicy +
    '; report-uri /csp-report/ ";';
  compilation.emitAsset('nginx-csp-header.conf', new RawSource(header));
}

module.exports = {
  {...},
  plugins: [
    new CspHtmlWebpackPlugin(
      {...}, {
      processFn: generateNginxHeaderFile
    })
  ]
};

In your nginx config:

location / {
  ...
  include /path/to/webpack/output/nginx-csp-header.conf
}

Contribution

Contributions are most welcome! Please see the included contributing file for more information.

License

This project is licensed under MIT. Please see the included license file for more information.