Webpack 5 "Module not found: ... node:crypto" - Fix Polyfill fallback

Webpack 5 stopped auto-polyfilling Node core modules (crypto, stream, buffer, path) for the browser. A dependency that imports them now fails to resolve unless you provide a fallback polyfill or tell Webpack the module is unused in the browser.

What this error means

A Webpack 5 build fails with Module not found: Error: Can't resolve 'crypto' plus the note "BREAKING CHANGE: webpack < 5 used to include polyfills for node.js core modules by default." It appears after upgrading to Webpack 5.

webpack output

Module not found: Error: Can't resolve 'crypto' in '/app/node_modules/some-lib'

BREAKING CHANGE: webpack < 5 used to include polyfills for node.js core
modules by default. This is no longer the case. ... install 'crypto-browserify'
and add resolve.fallback or set resolve.fallback to false.

Common causes

Dependency imports a Node core module

A browser-targeted dependency requires crypto/stream/buffer. Webpack 5 no longer ships a browser polyfill automatically, so resolution fails.

Server-only code reaching the browser bundle

Sometimes the import is a leak - a server-only module pulled into the client bundle - in which case a polyfill is the wrong fix and the dependency should be excluded instead.

How to fix it

Provide a browser polyfill fallback

Install the browser shim and map the module in resolve.fallback.

webpack.config.js

npm install -D crypto-browserify stream-browserify
// webpack.config.js
resolve: {
  fallback: {
    crypto: require.resolve('crypto-browserify'),
    stream: require.resolve('stream-browserify'),
  },
},

Or disable the fallback when truly unused

If the browser never needs the module, set its fallback to false so Webpack stubs it out.