LavaMoat Webpack Plugin

Putting lava in your pack. For security. We need to work on our metaphors.

LavaMoat Webpack Plugin wraps each module in the bundle in a Compartment and enforces LavaMoat Policies independently per package.

Usage

Policy generation is now built into the plugin. While it might get confused about aliases and custom resolvers, it should generally work even when they're in use.

1. Create a webpack bundle with the LavaMoat plugin enabled and the generatePolicy flag set to true
2. Make sure you add a <script src="./lockdown"></script> before all other scripts or enable the HtmlWebpackPluginInterop option if you're using html-webpack-plugin. (Note there's no .js there because it's the only way to prevent webpack from minifying the file thus undermining its security guarantees)
3. Tweak the policy if needed with policy-override.json

The plugin is emitting lockdown without the .js extension because that's the only way to prevent it from getting minified, which is likely to break it.

The LavaMoat plugin takes an options object with the following properties (all optional):

const LavaMoatPlugin = require('@lavamoat/webpack')

module.exports = {
  // ... other webpack configuration properties
  plugins: [
    new LavaMoatPlugin({
      generatePolicy: true,
      // ... settings from above, optionally
    }),
  ],
  // ... other webpack configuration properties
}

One important thing to note when using the LavaMoat plugin is that it disables the concatenateModules optimization in webpack. This is because concatenation won't work with wrapped modules.

Using static shims

Static shims are a way to include additional code in the runtime chunk before LavaMoat starts.

[!WARNING] Shims cannot use import or require, they must be standalone scripts.

const LavaMoatPlugin = require('@lavamoat/webpack')
const path = require('path')

module.exports = {
  plugins: [
    new LavaMoatPlugin({
      staticShims_experimental: [
        'package-name', // a package whose main export is a built standalone script
        path.join(__dirname, './local/file.js'),
      ],
    }),
  ],
}

The static shims are executed between the repair and harden phases of SES lockdown. It's the only way to polyfill functionality on intrinsics or run any privileged code outside of LavaMoat protections.

// resolvers-shim.js
  Promise.withResolvers = ...

Excluding modules

[!WARNING] This is an experimental feature and excluding may be configured differently in the future if this approach is proven insecure.

The default way to define specific behaviors for webpack is creating module rules. To ensure exclude rules are applied on the same exact files that match certain rules (the same RegExp may be matched against different things at different times) we're providing the exclude functionality as a loader you can add to the list of existing loaders or use individually.
The loader is available as LavaMoatPlugin.exclude from the default export of the plugin. It doesn't do anything to the code, but its presence is detected and treated as a mark on the file. Any file that's been processed by LavaMoatPlugin.exclude will not be wrapped in a Compartment.

[!NOTE] Exclude loader will only work when used in webpack config. Specifying it inline require('path/to/excludeLoader.js!./module.js') will not result in module.js being excluded. (This is a security feature to prevent your dependencies from declaring they want to be excluded.)

Example: avoid wrapping CSS modules:

  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          MiniCssExtractPlugin.loader,
          'css-loader',
          LavaMoatPlugin.exclude,
        ],
        // ...
      },
    ],
  },

See: examples/webpack.config.js for a complete example.

Scuttling GlobalThis

With defense-in-depth in mind, you can also make the actual globalThis unusable in case a reference to it is accidentally made accessible for a package. When enabled, this feature removes access to all globals after their copies were captured and passed to Compartments in LavaMoat. You can specify exceptions to maintain access to specific globals that are deliberately used outside of LavaMoat.

Configure scuttling using:

new LavaMoatPlugin({
  scuttleGlobalThis: {
    enabled: true,
    exceptions: [
      'yourRequiredGlobal',
      /RegExp matching globals that a webdriver depends on for running your tests/,
    ], // list of globals that should remain accessible
  },
})

diagnosticsVerbosity

Gotchas

Implicit modules

• Webpack may include dependencies polyfilling Node.js built-ins, such as the events or buffer packages. In other cases, it will ignore the built-ins and provide empty modules in their place (see below).

When a dependency (eg. buffer) is provided by Webpack, and you need to add it explicitly to your dependencies, you'll receive the following error:

Error: LavaMoat - Encountered unknown package directory for file "/home/(...)/node_modules/buffer/index.js"

Webpack-ignored modules

When a built-in Node.js module is ignored, Webpack generates something like this:

const nodeCrypto = __webpack_require__(/*! crypto */ '?0b7d')

A carveout is necessary in policy enforcement for these modules. Sadly, even treeshaking doesn't eliminate that module. It's left there and failing to work when reached by runtime control flow.

This plugin will skip policy enforcement for such ignored modules.

HMR

LavaMoat is not compatible with Hot Module Replacement (HMR) and is highly unlikely to ever be; HMR is the antithesis of sandboxing. If you wish to use HMR for development, disable LavaMoat in your dev configuration while keeping it enabled for production builds. You could keep lockdown added to the page if you wish to detect incompatibilities with the hardened environment early.

Security

This is an experimental software. Use at your own risk!

• SES lockdown must be added to the page without any bundling or transforming for any security guarantees to be sustained.
  • The plugin is attempting to add it as an asset to the compilation for the sake of Developer Experience. .js extension is omitted to prevent minification.
  • Optionally lockdown can be inlined into the bundle files. You need to declare which of the output files to inline lockdown runtime code to. These need to be the first file of the bundle that get loaded on the page.
    When you have a single bundle, you just configure a regex with one unique file name or a .*. It gets more complex with builds for multiple pages. The plugin doesn't attempt to guess where to inline lockdown.
    e.g. If you have 2 entries user.js and admin.js and a set up to suffix resulting bundles with commit id, you can use /user\.[a-f0-9]+\.js|admin\.[a-f0-9]+\.js/ to match the files.
• Each javascript module resulting from the webpack build is scoped to its package's policy

Threat Model

• Webpack itself is considered trusted.
• All plugins can bypass LavaMoat protections intentionally.
• It's unlikely but possible that a plugin can bypass LavaMoat protections unintentionally. Some of the warnings LavaMoat Plugin reports can help detect that.
• It should not be possible for loaders to bypass LavaMoat protections.
• Some plugins (eg. MiniCssExtractPlugin) execute code from the bundle at build time. To make the plugin work you need to trust it and the modules it runs and add the LavaMoat.exclude loader for them.
• This Webpack plugin does not protect against malicious execution by other third-party plugins at runtime (use LavaMoat for that).

Webpack runtime

Elements of the Webpack runtime (e.g., __webpack_require__.*) are currently mostly left intact. To avoid opening up potential bypasses, some functionality of the Webpack runtime is not available.

Module Federation depends on extending runtime in ways we would not expose to modules. We're open to contributions or collaboration on carefully enabling it.

Contributing

See DEVELOPMENT.md for notes on plans and roadmap. Refer to the main CONTRIBUTING.md for general guidelines on how to contribute.

Testing

Run npm test to start the automated tests.

Manual testing

• Navigate to example/
• Run npm ci and npm test
• Open dist/index.html in your browser and inspect the console