Fix CORS Error: Permission Denied for Unknown Address Space (Chrome PNA)

Have you ever deployed a web application that works perfectly at home or on a staging server, only to have it crash and burn when accessed inside your office network?

You open the console, expecting a simple syntax error, but instead, you are greeted with a terrifyingly vague network error:

“CORS error: Permission was denied for this request to access the unknown address space.”

If you are seeing this, you aren’t alone. This isn’t just a standard Cross-Origin Resource Sharing (CORS) issue; it is a security feature enforcement by Google Chrome known as Private Network Access (PNA).

In this guide, we will deconstruct why this error happens, why it specifically targets office networks and internal tools, and provide step-by-step solutions to get your application running again.

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What Is the “Permission Denied for Unknown Address Space” Error?

At its core, this error is a browser security block. It occurs when a public website (usually secure, served over HTTPS) tries to request resources from a device or server sitting on a private, local network (often HTTP).

Chrome classifies IP addresses into three distinct “Address Spaces”:

1. Public: The global internet (e.g., google.com, 8.8.8.8).
2. Private: Local Intranets (e.g., 192.168.1.50, 10.0.0.1, Intranet hostnames).
3. Local: The machine itself (e.g., localhost, 127.0.0.1).

The Rule: A “less secure” network (Public) cannot access a “more secure” network (Private or Local) without explicit permission.

When Chrome cannot strictly categorize the target IP—or when it detects you are crossing these boundaries without the right “Preflight” handshake—it throws the “Permission was denied for this request to access the unknown address space” error.

Why Does This Happen Only Inside Office Networks?

This behavior often confuses developers because the code works on localhost or typical home networks. However, office networks are complex.

In a corporate environment, you likely have:

• Internal DNS: Custom domains like http://internal-api.corp.
• Legacy Hardware: Old printers or IoT devices that only speak HTTP.
• VPNs: Virtual Private Networks that mask IPs.

When your public cloud dashboard (e.g., https://app.mycompany.com) tries to fetch data from http://internal-tool.local, Chrome flags this as a dangerous Private Network Access attempt. It assumes a malicious website might be trying to attack your router or internal servers (a technique called CSRF or Drive-by Pharming).

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Deep Dive: Chrome’s Private Network Access (PNA)

Google has been slowly rolling out the PNA specification (formerly known as CORS-RFC1918). The goal is to close the gap where the open internet can talk to your private devices.

How the Block Works

Before the browser sends the actual data (like a POST request), it sends a “Preflight” OPTIONS request.

If the request crosses from Public → Private, Chrome adds a special header:

Access-Control-Request-Private-Network: true

The server must respond with:

Access-Control-Allow-Private-Network: true

If your internal server doesn’t send this header (which most legacy servers don’t), Chrome blocks the request immediately, resulting in the “Permission was denied” error.

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4 Proven Solutions to Fix the Error

Depending on your control over the infrastructure, you can choose one of the following solutions.

Solution 1: HTTPS Everything (The Gold Standard)

The most robust fix is to ensure both the requesting site and the target internal service use HTTPS. If both are secure, the browser trusts the connection more readily, although Mixed Content rules may still apply.

Why this works: It removes the “Mixed Content” warning (HTTPS calling HTTP) and proves identity.

The Challenge: Getting a valid SSL certificate for an internal IP address (like 192.168.1.50) is difficult because public Certificate Authorities (CAs) do not issue certs for private IPs.

How to implement:

1. Use a real domain name for your internal service (e.g., intranet.mycompany.com).
2. Point the DNS A-record of that domain to the private IP (e.g., 10.0.0.5).
3. Generate a valid SSL certificate (Let’s Encrypt via DNS challenge works great here).
4. Install the cert on your internal server.

Solution 2: Implement PNA Headers (Server-Side Fix)

If you have access to the code of the internal server (the API or device you are calling), you can update it to support the PNA handshake.

You need to configure your server to handle the OPTIONS preflight request.

Step-by-Step for Node.js / Express:

JavaScript

app.use((req, res, next) => {
  // Standard CORS headers
  res.header("Access-Control-Allow-Origin", "https://your-public-site.com");
  res.header("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
  
  // REQUIRED for PNA
  res.header("Access-Control-Allow-Private-Network", "true");

  if (req.method === 'OPTIONS') {
    res.sendStatus(204);
  } else {
    next();
  }
});

Step-by-Step for Nginx:

If you are using Nginx as a reverse proxy for the internal tool:

Nginx

location / {
    if ($request_method = 'OPTIONS') {
        add_header 'Access-Control-Allow-Origin' 'https://your-public-site.com';
        add_header 'Access-Control-Allow-Private-Network' 'true';
        add_header 'Content-Type' 'text/plain; charset=utf-8';
        add_header 'Content-Length' 0;
        return 204;
    }
}

Note: The Access-Control-Allow-Origin cannot be * when using PNA. You must specify the exact origin.

Solution 3: Use a Reverse Proxy (The “Sidecar” Method)

If you cannot touch the internal server (e.g., it’s a locked-down IoT printer or an old legacy database), you can place a “Sidecar” proxy in front of it.

1. Set up a small Nginx or Node.js server inside your office network.
2. Configure this proxy to accept requests from your public app.
3. Inject the Access-Control-Allow-Private-Network: true header at the proxy level.
4. Forward the traffic to the legacy device.

Your public app talks to the Proxy, and the Proxy talks to the Legacy Device.

Solution 4: Enterprise Policy (For SysAdmins)

If you manage the office computers via Group Policy (GPO) or MDM, you can temporarily disable this check for specific origins.

Chrome Policy: InsecurePrivateNetworkRequestsAllowedForUrls

You can add your public domain to this allowlist.

• Key: InsecurePrivateNetworkRequestsAllowedForUrls
• Value: ["https://app.mycompany.com"]

Warning: This is a band-aid solution. Google intends to deprecate this policy eventually. It is useful for immediate firefighting but should not be your long-term strategy.

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Comparison of Solutions

Solution	Difficulty	Long-Term Viability	Best Use Case
HTTPS (DNS)	High	Excellent	Permanent production infrastructure.
PNA Headers	Medium	Good	Custom internal APIs you control.
Reverse Proxy	Medium	Good	Legacy hardware or locked devices.
Browser Policy	Low	Poor (Deprecated)	Quick fix for office employees only.

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Debugging: How to Confirm It Is PNA

Before you spend hours configuring servers, verify that PNA is the culprit.

1. Open Chrome DevTools (F12).
2. Go to the Network tab.
3. Trigger the request that fails.
4. Look for a failed request (Red text). Click on it.
5. Check the Console tab.

If you see a warning like this, it is definitely a PNA issue:

“The request from ‘https://public.com‘ to ‘http://local.server‘ was blocked because the request was made from a public address space to a private address space, and the preflight response did not answer with ‘Access-Control-Allow-Private-Network: true’.”

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Frequently Asked Questions (FAQs)

Here are the most common questions developers ask about the “CORS error unknown address space” issue.

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Conclusion and Next Steps

The “CORS error: Permission was denied for this request to access the unknown address space” is a sign that modern browser security is working as intended—even if it is frustrating. It protects internal networks from external threats.

To fix it reliably in your office network, you must stop treating internal apps as “hidden” and start treating them as “secure.”

Key Takeaways:

• Chrome blocks Public-to-Private network requests by default.
• You must send the Access-Control-Allow-Private-Network: true header.
• HTTPS is the best long-term solution, even for internal tools.
• Reverse proxies are the best friend of legacy hardware.