---
title: Security
description: A set of guidelines for building secure Electron apps
slug: security
hide_title: true
toc_max_heading_level: 3
---
# Security

:::info Reporting security issues
For information on how to properly disclose an Electron vulnerability,
see [SECURITY.md](../../SECURITY.md).

For upstream Chromium vulnerabilities: Electron keeps up to date with alternating
Chromium releases. For more information, see the
[Electron Release Timelines](../tutorial/electron-timelines.md) document.
:::

## Preface

As web developers, we usually enjoy the strong security net of the browser —
the risks associated with the code we write are relatively small. Our websites
are granted limited powers in a sandbox, and we trust that our users enjoy a
browser built by a large team of engineers that is able to quickly respond to
newly discovered security threats.

When working with Electron, it is important to understand that Electron is not
a web browser. It allows you to build feature-rich desktop applications with
familiar web technologies, but your code wields much greater power. JavaScript
can access the filesystem, user shell, and more. This allows you to build
high quality native applications, but the inherent security risks scale with
the additional powers granted to your code.

With that in mind, be aware that displaying arbitrary content from untrusted
sources poses a severe security risk that Electron is not intended to handle.
In fact, the most popular Electron apps (Atom, Slack, Visual Studio Code, etc)
display primarily local content (or trusted, secure remote content without Node
integration) — if your application executes code from an online source, it is
your responsibility to ensure that the code is not malicious.

## General guidelines

### Security is everyone's responsibility

It is important to remember that the security of your Electron application is
the result of the overall security of the framework foundation
(_Chromium_, _Node.js_), Electron itself, all NPM dependencies and
your code. As such, it is your responsibility to follow a few important best
practices:

* **Keep your application up-to-date with the latest Electron framework release.**
When releasing your product, you’re also shipping a bundle composed of Electron,
Chromium shared library and Node.js. Vulnerabilities affecting these components
may impact the security of your application. By updating Electron to the latest
version, you ensure that critical vulnerabilities (such as _nodeIntegration bypasses_)
are already patched and cannot be exploited in your application. For more information,
see "[Use a current version of Electron](#16-use-a-current-version-of-electron)".

* **Evaluate your dependencies.** While NPM provides half a million reusable packages,
it is your responsibility to choose trusted 3rd-party libraries. If you use outdated
libraries affected by known vulnerabilities or rely on poorly maintained code,
your application security could be in jeopardy.

* **Adopt secure coding practices.** The first line of defense for your application
is your own code. Common web vulnerabilities, such as Cross-Site Scripting (XSS),
have a higher security impact on Electron applications hence it is highly recommended
to adopt secure software development best practices and perform security testing.

### Isolation for untrusted content

A security issue exists whenever you receive code from an untrusted source (e.g.
a remote server) and execute it locally. As an example, consider a remote
website being displayed inside a default [`BrowserWindow`][browser-window]. If
an attacker somehow manages to change said content (either by attacking the
source directly, or by sitting between your app and the actual destination), they
will be able to execute native code on the user's machine.

:::warning
Under no circumstances should you load and execute remote code with
Node.js integration enabled. Instead, use only local files (packaged together
with your application) to execute Node.js code. To display remote content, use
the [`<webview>`][webview-tag] tag or a [`WebContentsView`][web-contents-view]
and make sure to disable the `nodeIntegration` and enable `contextIsolation`.
:::

:::info Electron security warnings
Security warnings and recommendations are printed to the developer console.
They only show up when the binary's name is Electron, indicating that a developer
is currently looking at the console.

You can force-enable or force-disable these warnings by setting
`ELECTRON_ENABLE_SECURITY_WARNINGS` or `ELECTRON_DISABLE_SECURITY_WARNINGS` on
either `process.env` or the `window` object.
:::

## Checklist: Security recommendations

You should at least follow these steps to improve the security of your application:

1. [Only load secure content](#1-only-load-secure-content)
2. [Do not enable Node.js integration for remote content](#2-do-not-enable-nodejs-integration-for-remote-content)
3. [Enable context isolation in all renderers](#3-enable-context-isolation)
4. [Enable process sandboxing](#4-enable-process-sandboxing)
5. [Use `ses.setPermissionRequestHandler()` in all sessions that load remote content](#5-handle-session-permission-requests-from-remote-content)
6. [Do not disable `webSecurity`](#6-do-not-disable-websecurity)
7. [Define a `Content-Security-Policy`](#7-define-a-content-security-policy) and use restrictive rules (i.e. `script-src 'self'`)
8. [Do not enable `allowRunningInsecureContent`](#8-do-not-enable-allowrunninginsecurecontent)
9. [Do not enable experimental features](#9-do-not-enable-experimental-features)
10. [Do not use `enableBlinkFeatures`](#10-do-not-use-enableblinkfeatures)
11. [`<webview>`: Do not use `allowpopups`](#11-do-not-use-allowpopups-for-webviews)
12. [`<webview>`: Verify options and params](#12-verify-webview-options-before-creation)
13. [Disable or limit navigation](#13-disable-or-limit-navigation)
14. [Disable or limit creation of new windows](#14-disable-or-limit-creation-of-new-windows)
15. [Do not use `shell.openExternal` with untrusted content](#15-do-not-use-shellopenexternal-with-untrusted-content)
16. [Use a current version of Electron](#16-use-a-current-version-of-electron)
17. [Validate the `sender` of all IPC messages](#17-validate-the-sender-of-all-ipc-messages)
18. [Avoid usage of the `file://` protocol and prefer usage of custom protocols](#18-avoid-usage-of-the-file-protocol-and-prefer-usage-of-custom-protocols)
19. [Check which fuses you can change](#19-check-which-fuses-you-can-change)
20. [Do not expose Electron APIs to untrusted web content](#20-do-not-expose-electron-apis-to-untrusted-web-content)

### 1. Only load secure content

Any resources not included with your application should be loaded using a
secure protocol like `HTTPS`. In other words, do not use insecure protocols
like `HTTP`. Similarly, we recommend the use of `WSS` over `WS`, `FTPS` over
`FTP`, and so on.

#### Why?

`HTTPS` has two main benefits:

1. It ensures data integrity, asserting that the data was not modified while in
   transit between your application and the host.
1. It encrypts the traffic between your user and the destination host, making it
   more difficult to eavesdrop on the information sent between your app and
   the host.

#### How?

```js title='main.js (Main Process)' @ts-type={browserWindow:Electron.BrowserWindow}
// Bad
browserWindow.loadURL('http://example.com')

// Good
browserWindow.loadURL('https://example.com')
```

```html title='index.html (Renderer Process)'
<!-- Bad -->
<script crossorigin src="http://example.com/react.js"></script>
<link rel="stylesheet" href="http://example.com/style.css">

<!-- Good -->
<script crossorigin src="https://example.com/react.js"></script>
<link rel="stylesheet" href="https://example.com/style.css">
```

### 2. Do not enable Node.js integration for remote content

:::info
This recommendation is the default behavior in Electron since 5.0.0.
:::

It is paramount that you do not enable Node.js integration in any renderer
([`BrowserWindow`][browser-window], [`WebContentsView`][web-contents-view], or
[`<webview>`][webview-tag]) that loads remote content. The goal is to limit the
powers you grant to remote content, thus making it dramatically more difficult
for an attacker to harm your users should they gain the ability to execute
JavaScript on your website.

After this, you can grant additional permissions for specific hosts. For example,
if you are opening a BrowserWindow pointed at `https://example.com/`, you can
give that website exactly the abilities it needs, but no more.

#### Why?

A cross-site-scripting (XSS) attack is more dangerous if an attacker can jump
out of the renderer process and execute code on the user's computer.
Cross-site-scripting attacks are fairly common - and while an issue, their
power is usually limited to messing with the website that they are executed on.
Disabling Node.js integration helps prevent an XSS from being escalated into a
so-called "Remote Code Execution" (RCE) attack.

#### How?

```js title='main.js (Main Process)'
// Bad
const mainWindow = new BrowserWindow({
  webPreferences: {
    contextIsolation: false,
    nodeIntegration: true,
    nodeIntegrationInWorker: true
  }
})

mainWindow.loadURL('https://example.com')
```

```js title='main.js (Main Process)'
// Good
const mainWindow = new BrowserWindow({
  webPreferences: {
    preload: path.join(app.getAppPath(), 'preload.js')
  }
})

mainWindow.loadURL('https://example.com')
```

```html title='index.html (Renderer Process)'
<!-- Bad -->
<webview nodeIntegration src="page.html"></webview>

<!-- Good -->
<webview src="page.html"></webview>
```

When disabling Node.js integration, you can still expose APIs to your website that
do consume Node.js modules or features. Preload scripts continue to have access
to `require` and other Node.js features, allowing developers to expose a custom
API to remotely loaded content via the [contextBridge API](../api/context-bridge.md).

### 3. Enable Context Isolation

:::info
Context Isolation is the default behavior in Electron since 12.0.0.
:::

Context isolation is an Electron feature that allows developers to run code
in preload scripts and in Electron APIs in a dedicated JavaScript context. In
practice, that means that global objects like `Array.prototype.push` or
`JSON.parse` cannot be modified by scripts running in the renderer process.

Electron uses the same technology as Chromium's [Content Scripts](https://developer.chrome.com/extensions/content_scripts#execution-environment)
to enable this behavior.

Even when `nodeIntegration: false` is used, to truly enforce strong isolation
and prevent the use of Node primitives `contextIsolation` **must** also be used.

Beware that _disabling context isolation_ for a renderer process by setting
`nodeIntegration: true` _also disables process sandboxing_ for that process.
See section below.

:::info
For more information on what `contextIsolation` is and how to enable it please
see our dedicated [Context Isolation](context-isolation.md) document.
:::

### 4. Enable process sandboxing

:::info
This recommendation is the default behavior in Electron since 20.0.0.

Additionally, process sandboxing can be enforced for all renderer processes
application wide: [Enabling the sandbox globally](sandbox.md#enabling-the-sandbox-globally)

_Disabling context isolation_ (see above) _also disables process sandboxing_,
regardless of the default, `sandbox: false` or globally enabled sandboxing!
:::

[Sandboxing](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/design/sandbox.md)
is a Chromium feature that uses the operating system to
significantly limit what renderer processes have access to. You should enable
the sandbox in all renderers. Loading, reading or processing any untrusted
content in an unsandboxed process, including the main process, is not advised.

:::info
For more information on what Process Sandboxing is and how to enable it please
see our dedicated [Process Sandboxing](sandbox.md) document.
:::

### 5. Handle session permission requests from remote content

You may have seen permission requests while using Chrome: they pop up whenever
the website attempts to use a feature that the user has to manually approve (
like notifications).

The API is based on the [Chromium permissions API](https://developer.chrome.com/extensions/permissions)
and implements the same types of permissions.

#### Why?

By default, Electron will automatically approve all permission requests unless
the developer has manually configured a custom handler. While a solid default,
security-conscious developers might want to assume the very opposite.

#### How?

```js title='main.js (Main Process)'
const { session } = require('electron')

const { URL } = require('node:url')

session
  .defaultSession
  .setPermissionRequestHandler((webContents, permission, callback) => {
    const parsedUrl = new URL(webContents.getURL())

    if (permission === 'notifications') {
      // Approves the permissions request
      callback(true)
    }

    // Verify URL
    if (parsedUrl.protocol !== 'https:' || parsedUrl.host !== 'example.com') {
      // Denies the permissions request
      return callback(false)
    }
  })
```

Note: `session.defaultSession` is only available after `app.whenReady` is called.

### 6. Do not disable `webSecurity`

:::info
This recommendation is Electron's default.
:::

You may have already guessed that disabling the `webSecurity` property on a
renderer process ([`BrowserWindow`][browser-window],
[`WebContentsView`][web-contents-view], or [`<webview>`][webview-tag]) disables
crucial security features.

Do not disable `webSecurity` in production applications.

#### Why?

Disabling `webSecurity` will disable the same-origin policy and set
`allowRunningInsecureContent` property to `true`. In other words, it allows
the execution of insecure code from different domains.

#### How?

```js title='main.js (Main Process)'
// Bad
const mainWindow = new BrowserWindow({
  webPreferences: {
    webSecurity: false
  }
})
```

```js title='main.js (Main Process)'
// Good
const mainWindow = new BrowserWindow()
```

```html title='index.html (Renderer Process)'
<!-- Bad -->
<webview disablewebsecurity src="page.html"></webview>

<!-- Good -->
<webview src="page.html"></webview>
```

### 7. Define a Content Security Policy

A Content Security Policy (CSP) is an additional layer of protection against
cross-site-scripting attacks and data injection attacks. We recommend that they
be enabled by any website you load inside Electron.

#### Why?

CSP allows the server serving content to restrict and control the resources
Electron can load for that given web page. `https://example.com` should
be allowed to load scripts from the origins you defined while scripts from
`https://evil.attacker.com` should not be allowed to run. Defining a CSP is an
easy way to improve your application's security.

#### How?

The following CSP will allow Electron to execute scripts from the current
website and from `apis.example.com`.

```plaintext
// Bad
Content-Security-Policy: '*'

// Good
Content-Security-Policy: script-src 'self' https://apis.example.com
```

#### CSP HTTP headers

Electron respects the [`Content-Security-Policy` HTTP header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy)
which can be set using Electron's
[`webRequest.onHeadersReceived`](../api/web-request.md#webrequestonheadersreceivedfilter-listener)
handler:

```js title='main.js (Main Process)'
const { session } = require('electron')

session.defaultSession.webRequest.onHeadersReceived((details, callback) => {
  callback({
    responseHeaders: {
      ...details.responseHeaders,
      'Content-Security-Policy': ['default-src \'none\'']
    }
  })
})
```

Note: `session.defaultSession` is only available after `app.whenReady` is called.

#### CSP meta tag

CSP's preferred delivery mechanism is an HTTP header. However, it is not possible
to use this method when loading a resource using the `file://` protocol. It can
be useful in some cases to set a policy on a page directly in the markup using a
`<meta>` tag:

```html title='index.html (Renderer Process)'
<meta http-equiv="Content-Security-Policy" content="default-src 'none'">
```

### 8. Do not enable `allowRunningInsecureContent`

:::info
This recommendation is Electron's default.
:::

By default, Electron will not allow websites loaded over `HTTPS` to load and
execute scripts, CSS, or plugins from insecure sources (`HTTP`). Setting the
property `allowRunningInsecureContent` to `true` disables that protection.

Loading the initial HTML of a website over `HTTPS` and attempting to load
subsequent resources via `HTTP` is also known as "mixed content".

#### Why?

Loading content over `HTTPS` assures the authenticity and integrity
of the loaded resources while encrypting the traffic itself. See the section on
[only displaying secure content](#1-only-load-secure-content) for more details.

#### How?

```js title='main.js (Main Process)'
// Bad
const mainWindow = new BrowserWindow({
  webPreferences: {
    allowRunningInsecureContent: true
  }
})
```

```js title='main.js (Main Process)'
// Good
const mainWindow = new BrowserWindow({})
```

### 9. Do not enable experimental features

:::info
This recommendation is Electron's default.
:::

Advanced users of Electron can enable experimental Chromium features using the
`experimentalFeatures` property.

#### Why?

Experimental features are, as the name suggests, experimental and have not been
enabled for all Chromium users. Furthermore, their impact on Electron as a whole
has likely not been tested.

Legitimate use cases exist, but unless you know what you are doing, you should
not enable this property.

#### How?

```js title='main.js (Main Process)'
// Bad
const mainWindow = new BrowserWindow({
  webPreferences: {
    experimentalFeatures: true
  }
})
```

```js title='main.js (Main Process)'
// Good
const mainWindow = new BrowserWindow({})
```

### 10. Do not use `enableBlinkFeatures`

:::info
This recommendation is Electron's default.
:::

Blink is the name of the rendering engine behind Chromium. As with
`experimentalFeatures`, the `enableBlinkFeatures` property allows developers to
enable features that have been disabled by default.

#### Why?

Generally speaking, there are likely good reasons if a feature was not enabled
by default. Legitimate use cases for enabling specific features exist. As a
developer, you should know exactly why you need to enable a feature, what the
ramifications are, and how it impacts the security of your application. Under
no circumstances should you enable features speculatively.

#### How?

```js title='main.js (Main Process)'
// Bad
const mainWindow = new BrowserWindow({
  webPreferences: {
    enableBlinkFeatures: 'ExecCommandInJavaScript'
  }
})
```

```js title='main.js (Main Process)'
// Good
const mainWindow = new BrowserWindow()
```

### 11. Do not use `allowpopups` for WebViews

:::info
This recommendation is Electron's default.
:::

If you are using [`<webview>`][webview-tag], you might need the pages and scripts
loaded in your `<webview>` tag to open new windows. The `allowpopups` attribute
enables them to create new [`BrowserWindows`][browser-window] using the
`window.open()` method. `<webview>` tags are otherwise not allowed to create new
windows.

#### Why?

If you do not need popups, you are better off not allowing the creation of
new [`BrowserWindows`][browser-window] by default. This follows the principle
of minimally required access: Don't let a website create new popups unless
you know it needs that feature.

#### How?

```html title='index.html (Renderer Process)'
<!-- Bad -->
<webview allowpopups src="page.html"></webview>

<!-- Good -->
<webview src="page.html"></webview>
```

### 12. Verify WebView options before creation

A WebView created in a renderer process that does not have Node.js integration
enabled will not be able to enable integration itself. However, a WebView will
always create an independent renderer process with its own `webPreferences`.

It is a good idea to control the creation of new [`<webview>`][webview-tag] tags
from the main process and to verify that their webPreferences do not disable
security features.

#### Why?

Since `<webview>` live in the DOM, they can be created by a script running on your
website even if Node.js integration is otherwise disabled.

Electron enables developers to disable various security features that control
a renderer process. In most cases, developers do not need to disable any of
those features - and you should therefore not allow different configurations
for newly created [`<webview>`][webview-tag] tags.

#### How?

Before a [`<webview>`][webview-tag] tag is attached, Electron will fire the
`will-attach-webview` event on the hosting `webContents`. Use the event to
prevent the creation of `webViews` with possibly insecure options.

```js title='main.js (Main Process)'
app.on('web-contents-created', (event, contents) => {
  contents.on('will-attach-webview', (event, webPreferences, params) => {
    // Strip away preload scripts if unused or verify their location is legitimate
    delete webPreferences.preload

    // Disable Node.js integration
    webPreferences.nodeIntegration = false

    // Verify URL being loaded
    if (!params.src.startsWith('https://example.com/')) {
      event.preventDefault()
    }
  })
})
```

Again, this list merely minimizes the risk, but does not remove it. If your goal
is to display a website, a browser will be a more secure option.

### 13. Disable or limit navigation

If your app has no need to navigate or only needs to navigate to known pages,
it is a good idea to limit navigation outright to that known scope, disallowing
any other kinds of navigation.

#### Why?

Navigation is a common attack vector. If an attacker can convince your app to
navigate away from its current page, they can possibly force your app to open
web sites on the Internet. Even if your `webContents` are configured to be more
secure (like having `nodeIntegration` disabled or `contextIsolation` enabled),
getting your app to open a random web site will make the work of exploiting your
app a lot easier.

A common attack pattern is that the attacker convinces your app's users to
interact with the app in such a way that it navigates to one of the attacker's
pages. This is usually done via links, plugins, or other user-generated content.

#### How?

If your app has no need for navigation, you can call `event.preventDefault()`
in a [`will-navigate`][will-navigate] handler. If you know which pages your app
might navigate to, check the URL in the event handler and only let navigation
occur if it matches the URLs you're expecting.

We recommend that you use Node's parser for URLs. Simple string comparisons can
sometimes be fooled - a `startsWith('https://example.com')` test would let
`https://example.com.attacker.com` through.

```js title='main.js (Main Process)'
const { app } = require('electron')

const { URL } = require('node:url')

app.on('web-contents-created', (event, contents) => {
  contents.on('will-navigate', (event, navigationUrl) => {
    const parsedUrl = new URL(navigationUrl)

    if (parsedUrl.origin !== 'https://example.com') {
      event.preventDefault()
    }
  })
})
```

### 14. Disable or limit creation of new windows

If you have a known set of windows, it's a good idea to limit the creation of
additional windows in your app.

#### Why?

Much like navigation, the creation of new `webContents` is a common attack
vector. Attackers attempt to convince your app to create new windows, frames,
or other renderer processes with more privileges than they had before; or
with pages opened that they couldn't open before.

If you have no need to create windows in addition to the ones you know you'll
need to create, disabling the creation buys you a little bit of extra
security at no cost. This is commonly the case for apps that open one
`BrowserWindow` and do not need to open an arbitrary number of additional
windows at runtime.

#### How?

[`webContents`][web-contents] will delegate to its
[window open handler][window-open-handler] before creating new windows. The handler will
receive, amongst other parameters, the `url` the window was requested to open
and the options used to create it. We recommend that you register a handler to
monitor the creation of windows, and deny any unexpected window creation.

```js title='main.js (Main Process)' @ts-type={isSafeForExternalOpen:(url:string)=>boolean}
const { app, shell } = require('electron')

app.on('web-contents-created', (event, contents) => {
  contents.setWindowOpenHandler(({ url }) => {
    // In this example, we'll ask the operating system
    // to open this event's url in the default browser.
    //
    // See the following item for considerations regarding what
    // URLs should be allowed through to shell.openExternal.
    if (isSafeForExternalOpen(url)) {
      setImmediate(() => {
        shell.openExternal(url)
      })
    }

    return { action: 'deny' }
  })
})
```

### 15. Do not use `shell.openExternal` with untrusted content

The shell module's [`openExternal`][open-external] API allows opening a given
protocol URI with the desktop's native utilities. On macOS, for instance, this
function is similar to the `open` terminal command utility and will open the
specific application based on the URI and filetype association.

#### Why?

Improper use of [`openExternal`][open-external] can be leveraged to compromise
the user's host. When openExternal is used with untrusted content, it can be
leveraged to execute arbitrary commands.

#### How?

```js title='main.js (Main Process)' @ts-type={USER_CONTROLLED_DATA_HERE:string}
//  Bad
const { shell } = require('electron')

shell.openExternal(USER_CONTROLLED_DATA_HERE)
```

```js title='main.js (Main Process)'
//  Good
const { shell } = require('electron')

shell.openExternal('https://example.com/index.html')
```

### 16. Use a current version of Electron

You should strive for always using the latest available version of Electron.
Whenever a new major version is released, you should attempt to update your
app as quickly as possible.

#### Why?

An application built with an older version of Electron, Chromium, and Node.js
is an easier target than an application that is using more recent versions of
those components. Generally speaking, security issues and exploits for older
versions of Chromium and Node.js are more widely available.

Both Chromium and Node.js are impressive feats of engineering built by
thousands of talented developers. Given their popularity, their security is
carefully tested and analyzed by equally skilled security researchers. Many of
those researchers [disclose vulnerabilities responsibly][responsible-disclosure],
which generally means that researchers will give Chromium and Node.js some time
to fix issues before publishing them. Your application will be more secure if
it is running a recent version of Electron (and thus, Chromium and Node.js) for
which potential security issues are not as widely known.

#### How?

Migrate your app one major version at a time, while referring to Electron's
[Breaking Changes][breaking-changes] document to see if any code needs to
be updated.

### 17. Validate the `sender` of all IPC messages

You should always validate incoming IPC messages `sender` property to ensure you
aren't performing actions or sending information to untrusted renderers.

#### Why?

All Web Frames can in theory send IPC messages to the main process, including
iframes and child windows in some scenarios.  If you have an IPC message that returns
user data to the sender via `event.reply` or performs privileged actions that the renderer
can't natively, you should ensure you aren't listening to third party web frames.

You should be validating the `sender` of **all** IPC messages by default.

#### How?

```js title='main.js (Main Process)' @ts-type={getSecrets:()=>unknown}
// Bad
ipcMain.handle('get-secrets', () => {
  return getSecrets()
})

// Good
ipcMain.handle('get-secrets', (e) => {
  if (!validateSender(e.senderFrame)) return null
  return getSecrets()
})

function validateSender (frame) {
  // Validate the host of the URL using an actual URL parser and an allowlist
  if ((new URL(frame.url)).host === 'electronjs.org') return true
  return false
}
```

### 18. Avoid usage of the `file://` protocol and prefer usage of custom protocols

You should serve local pages from a custom protocol instead of the `file://` protocol.

#### Why?

The `file://` protocol gets more privileges in Electron than in a web browser and even in
browsers it is treated differently to http/https URLs. Using a custom protocol allows you
to be more aligned with classic web url behavior while retaining even more control about
what can be loaded and when.

Pages running on `file://` have unilateral access to every file on your machine meaning
that XSS issues can be used to load arbitrary files from the users machine. Using a custom
protocol prevents issues like this as you can limit the protocol to only serving a specific
set of files.

#### How?

Follow the [`protocol.handle`](../api/protocol.md#protocolhandlescheme-handler) examples to
learn how to serve files / content from a custom protocol.

### 19. Check which fuses you can change

Electron ships with a number of options that can be useful but a large portion of
applications probably don't need. In order to avoid having to build your own version of
Electron, these can be turned off or on using [Fuses](./fuses.md).

#### Why?

Some fuses, like `runAsNode` and `nodeCliInspect`, allow the application to behave differently
when run from the command line using specific environment variables or CLI arguments. These
can be used to execute commands on the device through your application.

This can let external scripts run commands that they potentially would not be allowed to, but
that your application might have the rights for.

#### How?

[`@electron/fuses`](https://npmjs.com/package/@electron/fuses) is a module we made to make
flipping these fuses easy. Check out the README of that module for more details on usage and
potential error cases, and refer to
[How do I flip fuses?](./fuses.md#how-do-i-flip-fuses) in our documentation.

### 20. Do not expose Electron APIs to untrusted web content

You should not directly expose Electron's APIs, especially IPC, to untrusted web content in your
preload scripts.

#### Why?

Exposing raw APIs like `ipcRenderer.on` is dangerous because it gives renderer processes direct
access to the entire IPC event system, allowing them to listen for any IPC events, not just the ones
intended for them.

To avoid that exposure, we also cannot pass callbacks directly through: The first
argument to IPC event callbacks is an `IpcRendererEvent` object, which includes properties like `sender`
that provide access to the underlying `ipcRenderer` instance. Even if you only listen for specific
events, passing the callback directly means the renderer gets access to this event object.

In short, we want the untrusted web content to only have access to necessary information and APIs.

#### How?

```js title='preload'.js'
// Bad
contextBridge.exposeInMainWorld('electronAPI', {
  on: ipcRenderer.on
})

// Also bad
contextBridge.exposeInMainWorld('electronAPI', {
  onUpdateCounter: (callback) => ipcRenderer.on('update-counter', callback)
})

// Good
contextBridge.exposeInMainWorld('electronAPI', {
  onUpdateCounter: (callback) => ipcRenderer.on('update-counter', (_event, value) => callback(value))
})
```

:::info
For more information on what `contextIsolation` is and how to use it to secure your app,
please see the [Context Isolation](context-isolation.md) document.
:::

[breaking-changes]: ../breaking-changes.md
[browser-window]: ../api/browser-window.md
[webview-tag]: ../api/webview-tag.md
[web-contents-view]: ../api/web-contents-view.md
[responsible-disclosure]: https://en.wikipedia.org/wiki/Responsible_disclosure
[web-contents]: ../api/web-contents.md
[window-open-handler]: ../api/web-contents.md#contentssetwindowopenhandlerhandler
[will-navigate]: ../api/web-contents.md#event-will-navigate
[open-external]: ../api/shell.md#shellopenexternalurl-options
