Microsoft has acknowledged that the recent Windows 11 update, KB5066835, is causing significant disruptions, particularly affecting localhost (127.0.0.1) HTTP/2 connections. This issue prevents locally hosted applications from connecting to the network, creating a ripple effect of complications for users on versions 24H2 and 25H2.
- Installation of the October 2025 Patch Tuesday update may fail due to various error codes, including 0x800f0922, 0x800f0983, 0x800f081f, 0x80071a2d, and 0x800f0991. Users encountering these errors are advised to download the patch directly from the Update Catalog or utilize the Media Creation Tool for an in-place upgrade to 25H2, as online solutions have proven ineffective.
- A bug is obstructing File Explorer’s document previews in the Preview pane, erroneously citing security concerns.
- Compatibility issues have arisen with certain Logitech peripherals, rendering them non-functional.
- Users are also reporting that mouse and keyboard inputs are unresponsive in the Windows Recovery Environment (WinRE).
Despite being a mandatory security update, KB5066835 has introduced a series of noteworthy features, such as the ability to reposition on-screen volume indicators and enhance the loading speed of File Explorer’s context menu. However, these enhancements come at a cost, as the update has inadvertently disrupted critical functionalities.
October 2025 Patch Tuesday updates break localhost (127.0.0.1) HTTP/2 connections
For developers relying on localhost for debugging applications, the impact of this update has been particularly pronounced. After installation, many users found themselves unable to connect to 127.0.0.1, leading to persistent error messages like “ERRCONNECTIONRESET” and “ERRHTTP2PROTOCOL_ERROR” across various browsers.
Microsoft has confirmed that the issue is not confined to specific development environments. Affected users have reported similar problems when attempting to debug Flutter-based web applications. The root of the problem lies in a regression within the kernel-mode HTTP server (HTTP.sys), which mishandles HTTP/2 handshakes, resulting in connection resets.
As Microsoft stated, “After recent Windows updates, IIS websites might fail to load, displaying a message such as ‘Connection reset – error (ERRCONNECTIONRESET)’ or similar error. This includes websites hosted on http://localhost/ and other IIS connections.” The scale of this issue is substantial, as it disrupts any server-side applications dependent on HTTP.sys.
- ERRCONNECTIONRESET
- ERRHTTP2PROTOCOL_ERROR
How to fix localhost issues after the October 2025 update KB5066835 in Windows 11 24H2/25H2?
In response to these issues, Microsoft is rolling out an emergency patch aimed at resolving localhost-related problems. However, users should be prepared for a potential wait of over 48 hours for the fix to appear on their systems. Affected individuals are encouraged to check for updates and reboot their PCs, even if no new updates are displayed, to expedite the patch retrieval process.
For those still facing difficulties, a workaround involves modifying the Windows Registry using the following PowerShell script:
New-ItemProperty -Path 'HKLM:SYSTEMCurrentControlSetServicesHTTPParameters' -Name 'EnableHttp2Tls' -PropertyType DWord -Value 0 -Force New-ItemProperty -Path 'HKLM:SYSTEMCurrentControlSetServicesHTTPParameters' -Name 'EnableHttp2Cleartext' -PropertyType DWord -Value 0 -Force
This command creates two DWORD (32-bit) values, EnableHttp2Tls and EnableHttp2Cleartext, both set to zero. This adjustment disables HTTP/2, reverting the system to HTTP/1.1, thereby restoring localhost/HTTP/2 connections.
Windows 11 KB5066835 breaks File Explorer’s preview pane
File Explorer’s functionality has also been compromised due to this update. The Preview pane, which allows users to view documents such as PDFs without opening them, is now plagued by a security alert that states: The file you are attempting to preview could harm your computer. If you trust the file and the source you received it from, open it to view its content. This issue predominantly affects files downloaded from cloud storage or office networks, while locally created PDFs remain unaffected.
How to fix “The file you are attempting to preview could harm your computer” error in File Explorer after Windows update
While uninstalling Windows 11 KB5066835 may resolve the preview issue, it is not advisable to remove security updates. Instead, users can explore alternative solutions:
1. Unblock files using PowerShell (recommended)
This command disables Windows 11’s security feature for specific file types in designated directories. Users should adjust the path to match their file locations.
2. Completely disable File Explorer’s built-in security for file previews.
- Open Regedit (Registry Editor).
- Navigate to:
ComputerHKEYCURRENTUSERSoftwareMicrosoftWindowsCurrentVersionPolicies
- Create a new key named “Attachments.” Within it, create a new DWORD (32-bit) value.
- Set the DWORD to SaveZoneInformation and its value to 1.
This method disables the security feature entirely, but the PowerShell script to unblock PDFs is generally more efficient.
Logitech premium features have stopped working for some users
Following the October 2025 Update, users have reported that Logitech’s specialized shortcuts and features have ceased to function. For instance, the side buttons on the MX Anywhere 3 mouse are unresponsive, disrupting functionalities like zooming and keyboard mapping.
Keyboard and mouse stopped working in WinRE (Windows Recovery) after the October 2025 Update
Reports have surfaced indicating that Windows 11 KB5066835 may disrupt the Windows Recovery Environment (WinRE), which is essential for recovering malfunctioning PCs. Although WinRE itself remains operational, users are unable to interact with it due to non-responsive keyboard and mouse inputs.
While it remains uncertain whether Microsoft is aware of this issue, affected users can disable WinRE using the command reagentc /disable, then replace the WinRE image (winre.wim) with one from the Windows 11 25H2 ISO. After replacing the file, users can re-enable WinRE with reagentc /enable. However, these steps are recommended only for IT administrators who are familiar with the process.
