How to fix LocalHost issue after installing update KB5066835 on Windows 11

• October 2025 Security Update for Windows 11 25H2 and 24H2 breaks LocalHost connection.
• Microsoft has already resolved this issue with a Known Issue Rollback (KIR) release.
• However, you can also fix this issue manually by editing the Registry.

Microsoft has confirmed an issue after installing the Windows 11 October 2025 Security Update (KB5066835) on versions 25H2 and 24H2 that prevents websites from loading using the LocalHost (127.0.0.1) HTTP/2 connection.

LocalHost is a reserved hostname that refers to your own computer. It acts as an internal loopback address, specifically the IP address 127.0.0.1 (for IPv4). When you send a network request to LocalHost, the data is redirected back to your machine by the operating system, bypassing your network card and the internet.

According to Microsoft’s information, after installing builds 26100.6899 and 26200.6899, “server-side applications that rely on HTTP.sys may experience issues with incoming connections. As a result, IIS websites might fail to load, displaying a message such as “Connection reset – error (ERR_CONNECTION_RESET)”, or similar error. This includes websites hosted on http://localhost/, and other IIS connections.”

The company also notes that due to a “variety of conditions” that can influence this problem, this particular issue is not happening on every device.

If you’re experiencing this issue, the company is rolling out a Known Issue Rollback (KIR) package that allows you to undo a specific problematic change introduced by a recent update without requiring you to uninstall the entire update. If this doesn’t resolve the problem, you can run a few commands to fix it manually.

In this guide, I’ll outline the different ways to fix the LocalHost problem on Windows 11.

Fix LocalHost problem after installing update KB5066835 on Windows 11

You can try to resolve this networking issue in two ways.

Resolve LocalHost issue automatically

To install the Known Issue Rollback package on Windows 11 manually, follow these steps:

1. Open Settings on Windows 11.

2. Click on Windows Update.

3. Click the Check for updates button.

   

4. Click the Restart now button.

Once you complete the steps, if the fix is available for your computer, it will download and install automatically on Windows 11.

Resolve LocalHost issue manually

To fix the IIS problem affecting the LocalHost connection, follow these steps:

1. Open Start.

2. Search for PowerShell (or Terminal), right-click the top result, and select the Run as administrator option.

3. Type the following command to create the EnableHttp2Tls DWORD and set it to zero, and press Enter:

   New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Services\HTTP\Parameters' -Name 'EnableHttp2Tls' -PropertyType dword -Value 0 -Force

4. Type the following command to create the EnableHttp2Cleartext DWORD and set it to zero, and press Enter:

   New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Services\HTTP\Parameters' -Name 'EnableHttp2Cleartext' -PropertyType dword -Value 0 -Force

   

5. Restart the computer.

After you complete the steps, web applications running locally should load correctly on Windows 11.