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Prevents access to dev server from unknown IPs


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The package prevents uncontrollable access to dev server by asking manual approve from the developer when someone connects to the server from unknown IP.



When frontend developers run webpack-dev-server on localhost they sometimes want to check the result on the different devices (e.g. smartphones, tablets). By default it's hard to do, because the server is bound on and isn't allowed to receive connections from other computers.

So, most of the time developers rebind server to (by setting host option in webpack config) to make it available over the local network. But at the same time it grants anyone from the same network a permission to connect to the server, see the project and steal the code. Usually dev servers also serve source maps, which makes the source code fully visible too.

Such dev server setup may harm even pet-projects if there are any sensitive credentials in the source code.

This firewall prevents unwanted connection to the server. It intercepts all the incoming requests, checks their hosts' IPs against the list of allowed ones, and passes them through or denies.


npm install --save-dev @funboxteam/webpack-dev-server-firewall


To use the package add it into your project's webpack config in devServer.setupMiddlewares:

const firewall = require('@funboxteam/webpack-dev-server-firewall');


import { firewall } from '@funboxteam/webpack-dev-server-firewall';

module.exports = {
  // ...
  devServer: {
    // ...
    setupMiddlewares: (middlewares, devServer) => {
      // ...
      return middlewares;

For older webpack-dev-server versions use:

  • devServer.onBeforeSetupMiddleware for <4.7.0;
  • devServer.before for <4.0.0;
  • devServer.setup for <2.9.0.

firewall function expects an Express application as an argument.

It's important to run firewall before others hooks.

How it works

By default the package allows requests from only. When the request from other IP appears the package asks for developer's approve in the terminal where webpack-dev-server is running:

Child serviceworker-plugin:
     1 asset
    Entrypoint undefined = sw.js
    [./src/app/sw.js] 2.82 KiB {0} [built]
ℹ 「wdm」: Compiled with warnings.
# ↑ webpack log is trying to get access to the server. Allow? [yes / no]:

If the developer approves the connection, IP is added into the list of known hosts, and all the next connections will be allowed automatically. has been added to known hosts.

If the developer denies the connection, the client using that IP will get response with 403 HTTP code.

Important details

  1. The package does not work as a filter of unwanted connections.

    If the developer denies the connection once, it doesn't mean that it will be ignored in the future. In case of reconnection from the suspicious IP, the package will ask for developer's approval again.

    It works this way to be sure that the developer will be notified about all the suspicious incoming connections.

  2. The package does not guarantee complete protection against intruders.

    The package doesn't check in any ways that the client IP belongs to the same computer that it did when the IP was allowed. It means that when the DHCP settings are changed (or much easier: when the developer connects to the different network) the rules of addresses distribution will be changed too, and the earlier allowed address may be allocated to the new computer, which may be used by the intruder.

    To improve the security level clear the list of allowed IPs every time you run the server. Check out “Additional” section for details.

  3. List of known IP addresses is stored in ~/.funbox_webpack_known_hosts.

    If you want to remove any IP from the known hosts, you can make it manually.

    Among other things, this means that the list of allowed IPs is the same for all projects running on the machine.

  4. To avoid confusion the package expects a clear yes as request confirmation.

    Short answer such as y is not allowed. Any other answer except yes means no.



The package has small CLI which allows to clear the list of allowed IPs:

webpack-dev-server-firewall forget-known-hosts

It's important to note that when the firewall starts the list of allowed IPs is loaded from the file and stored in RAM. So, one should use the described above CLI command when the server is stopped. Otherwise the file may be overwritten by the firewall instance.


Besides the onBeforeSetupMiddleware hook the packages exports forgetKnownHosts method that can be used for clearing the list of allowed IPs from JS script.

E.g. the code below clears the list on every server start:

const firewall = require('@funboxteam/webpack-dev-server-firewall');


module.exports = {
  // ...
  devServer: {
    // ...
    onBeforeSetupMiddleware: firewall,


Sponsored by FunBox