Fix NS_E_CURL_INVALIDHOSTNAME (0XC00D1326) - Quick Steps

Quick answer

Flush your DNS cache (ipconfig /flushdns), check the URL for typos, and disable any active proxy or VPN that might be intercepting traffic. That fixes 90% of cases.

Why this happens

The NS_E_CURL_INVALIDHOSTNAME error (0XC00D1326) pops up when Windows can't translate the host part of a URL to an IP address. Common triggers: you mistyped the URL, your DNS server is down or returning garbage, a proxy or VPN is injecting a bad route, or the hosts file (C:\Windows\System32\drivers\etc\hosts) has a corrupted or conflicting entry. I've seen this most often in Windows Media Player and old streaming apps that don't handle DNS failures gracefully.

Don't waste time reinstalling apps or drivers — the network stack is almost always the culprit.

Step-by-step fix

Check the URL for typos. Look for extra dots, missing slashes, or swapped characters. The hostname has to match exactly — http://example.cmo won't work.
Flush DNS resolver cache. Open Command Prompt as admin and run:
```
ipconfig /flushdns
```
Then ipconfig /registerdns. This clears any stale or corrupted entries.
Reset Winsock. Still broken? Run netsh winsock reset and reboot. This wipes out any left-over socket configurations from old VPNs or proxies.
Test DNS manually. Ping the hostname:
```
ping example.com
```
If it fails, try nslookup example.com. If that also fails, your DNS server is the problem. Switch to Google's DNS (8.8.8.8 and 8.8.4.4) temporarily to confirm.
Disable proxy and VPN. Go to Settings > Network & Internet > Proxy, turn off “Use a proxy server”. Also disable any VPN client. Restart the app that threw the error.
Check the hosts file. Open C:\Windows\System32\drivers\etc\hosts in Notepad as admin. Look for any line referencing the hostname you're trying to reach. If it's there and pointing to a wrong IP, comment it out with a # at the start of the line.

Alternative fixes if the main steps fail

Reset network stack completely. In an admin command prompt, run:

netsh int ip reset
netsh winsock reset
ipconfig /release
ipconfig /renew
ipconfig /flushdns

Reboot.

Turn off IPv6. Some older apps don't handle IPv6 hostnames well. Go to Network Adapter settings, uncheck “Internet Protocol Version 6 (TCP/IPv6)”, and reboot.
Use a different DNS server globally. Set your adapter to use Cloudflare (1.1.1.1) or Google (8.8.8.8). Don't bother with OpenDNS — it's slower.
Run the Windows Network Troubleshooter. It's basic, but I've seen it fix DNS issues in Windows 10/11 when nothing else did. Right-click the network icon > Troubleshoot problems.

Prevention tip

Set your DNS to a public resolver at the router level. This avoids ISP DNS problems that cause exactly this error. Also, never let apps install proxy settings — always disable “Automatically detect settings” in Internet Options > Connections > LAN settings. That checkbox is a magnet for broken proxy configs.

One more thing: if you use a corporate VPN, this error often means the VPN DNS suffix isn't set correctly. Talk to your network admin before trying anything drastic.