Why Chrome Restricts Local Network Access (& How to Adapt)

As web applications increasingly interact with modern devices like printers, IoT hardware, and backend servers on local networks, security vulnerabilities have also grown in tandem. To bolster browser security and protect users from potential attacks, Chrome has implemented restrictions on local network access starting from version 142. While these changes add an essential layer of defense, they present challenges for developers trying to maintain compatibility. In this article, we’ll explore why Chrome restricts local network access, how it impacts web development, and what steps you can take to adapt your applications.

A Look at Chrome’s Local Network Access Policy

Google introduced the Local Network Access (LNA) policy as part of its broader initiative to enhance browser security. Local network access, which allows web applications to communicate with devices or servers within the same local network, is inherently risky. Without proper restrictions, attackers could exploit this flexibility to launch cross-site request forgery (CSRF) attacks, steal sensitive data, or hijack network devices.

From Chrome version 142 onwards, requests to local network resources (e.g., http://127.0.0.1 or http://192.168.0.1) are blocked entirely unless explicit user permission is granted. This restriction supports Chrome's permissions model, requiring websites to request access explicitly through permissions policies or user prompts.

Why was this necessary? Consider a malicious script running on an unknown website. Without restrictions, the script could quietly interact with a user’s router or other local devices, potentially altering configurations, stealing private keys, or worse. By restricting access, Chrome ensures that only trusted applications granted specific permissions by the user can access local network resources.

How it Works: The New Local Network Request Workflow

When a website tries to access a local network resource for the first time, Chrome triggers a permission prompt. The user is then tasked with deciding whether to allow that website access to local network resources. This process involves several security checks:

Preflight Requests: Chrome sends an HTTP OPTIONS preflight request to ensure the resource’s endpoint explicitly allows cross-origin resource sharing (CORS). If the preflight fails, the main request is blocked.
Permissions Prompt: The browser displays a dialog asking the user to allow or block the request. This permission is stored persistently for the given website.
Address Space Requirements: Using the browser’s targetAddressSpace option, requests must define whether the destination is local, private, or loopback. Incorrect configurations result in blocked requests.

Implementing Address Space in Fetch Requests

Here’s an example of how to specify the address space in a fetch call for a local server:

fetch('http://127.0.0.1:8080/resource', {
  method: 'GET',
  targetAddressSpace: 'loopback' // Ensures the browser knows this is a loopback address
})
  .then((response) => {
    if (response.ok) {
      return response.json();
    }
    throw new Error('Failed to fetch resource');
  })
  .then((data) => console.log('Resource fetched:', data))
  .catch((error) => console.error('Error:', error));

If the targetAddressSpace doesn’t match the resource’s actual location, Chrome will reject the request with an error.

Adapting Your Application to Chrome’s Restrictions

As a developer, adapting to these changes involves updating your application to comply with Chrome’s restrictions while ensuring seamless functionality for end users.

Update HTTP Headers

Ensure local servers you're accessing respond with proper HTTP headers, including CORS and the new Access-Control-Allow-Private-Network header. For example:

Access-Control-Allow-Origin: https://your-app.com
Access-Control-Allow-Methods: GET, POST
Access-Control-Allow-Credentials: true
Access-Control-Allow-Private-Network: true

This response header explicitly tells Chrome that requests to private network endpoints from your website are allowed.

Enable `local-network-access` for Iframes

If your application embeds nested iframes, you’ll need to delegate local network access permissions. Add the allow="local-network-access" attribute to iframe elements:

<iframe 
    src="https://nested-app.com" 
    allow="local-network-access">
</iframe>

Without this, requests originating from within iframe contexts may fail.

Use the Permissions API

Using the Permissions API, websites can proactively check for the local-network-access permission status and customize user flows based on it:

navigator.permissions.query({ name: 'local-network-access' })
  .then((result) => {
    console.log('Local Network Access Permission:', result.state);
    if (result.state === 'granted') {
      console.log('Access allowed');
    } else if (result.state === 'denied') {
      console.warn('Access denied');
    } else {
      console.log('Permission not yet requested');
    }
  });

Case Studies: Handling Edge Cases and Best Practices

Case Study 1: IoT Device Configuration

An IoT dashboard needs to communicate with smart devices on a user’s local network. After implementing the proper permissions policies, the dashboard includes an onboarding flow that explains why users need to grant local network access. Success rates for onboarding increased by 25% after clearly articulating the need and purpose of the permissions.

Case Study 2: GeoComply and Nested Iframes

GeoComply relies heavily on localhost services for user authentication. After Chrome restrictions broke functionality, the engineering team updated their application with precise allow="local-network-access" attributes and addressed all preflight CORS requirements. This led to a successful deployment compatible with Chrome v142+.

Why This Matters: The Broader Security Landscape

Chrome’s move to restrict local network access stems from a significant rise in reported vulnerabilities affecting IoT and local devices. Attack scenarios previously overlooked are now well-understood, including DNS rebinding, printer hijacking, and unintentional device exposure. By enforcing these restrictions, Chrome aims to raise the security baseline across all applications.

For developers, these changes represent a trade-off: increased effort in implementation but stronger security for users. While adjustments like updating headers or re-architecting iframe applications may require an upfront investment, they future-proof your application against emerging threats.

Conclusion: Embracing a Safer, More Secure Web

Chrome’s decision to restrict local network access is a pivotal step toward addressing known security vulnerabilities in modern web applications. While adapting to these changes may seem daunting at first, the prescribed tools—like preflight requests, header updates, and permissions policies—ultimately create an ecosystem where users can feel secure browsing the web.

For developers, now is the time to evaluate your applications, identify potential blockers, and implement solutions that align with these new policies. By working with Chrome’s restrictions, you’re not only building functionality into your projects, but also setting a stronger foundation for secure and ethical development in the evolving web landscape.