Microsoft Confirms Emergency Patch After Localhost and WinRE Breakages
Just days after Microsoft ended security support for nearly 500 million Windows 10 users, a new issue has hit Windows 11 systems. The latest mandatory security update, KB5066835, has caused widespread problems, prompting Microsoft to issue an emergency fix within 48 hours.
According to reports from Windows Latest and The Register, the update breaks localhost network connections, rendering locally hosted apps unable to communicate with the system. Additionally, the patch has triggered installation errors and disabled certain key peripherals, including Logitech mice and keyboards, especially within the Windows Recovery Environment (WinRE).
Microsoft has acknowledged the issue, stating that it “breaks localhost connections, meaning locally hosted apps can no longer connect to your network.” Users are advised not to attempt manual fixes or online registry edits, as many circulating “solutions” are ineffective or potentially harmful. Instead, the company urges affected users to check for updates and reboot their systems while awaiting the official patch rollout.
Technical Breakdown: HTTP.sys Regression at the Core
Windows Latest identified a regression in the kernel-mode HTTP server (HTTP.sys), which mishandles HTTP/2 handshakes on loopback connections to 127.0.0.1. This error effectively breaks Internet Information Services (IIS)
“The update broke IIS, which affects anything behind HTTP.sys,” the report noted. “Windows is designed to handle 127.0.0.1 requests by loading the HTTP/2 session in the kernel, which then routes to the IIS worker or your app. Now that chain collapses.”
While the issue seems widespread, The Register reported that it does not occur on clean installations of Windows 11 24H2, suggesting that the bug may stem from a conflict with existing configurations rather than a flaw in the update code itself.
Peripheral and WinRE Failures Confirmed
Following the initial acknowledgment of the localhost issue, Microsoft has also confirmed failures within the Windows Recovery Environment (WinRE). Users attempting to repair or reset their systems now find that the mouse and keyboard are completely unresponsive, making the recovery interface unusable.
“In practice, the issue makes it impossible to navigate between recovery options,” said Windows Latest. “If you try to troubleshoot or reset Windows, you simply can’t — the cursor doesn’t move, and the keyboard doesn’t respond.” This problem also affects newly upgraded systems from Windows 10.
Some independent workarounds exist, but they require modifying system files, which experts strongly discourage unless users are highly experienced. Incorrect edits could render Windows unstable or prevent it from booting altogether.
Microsoft’s Response and User Options
Microsoft says an emergency update is now being deployed to fix the localhost and WinRE issues for Windows 11 versions 24H2 and 25H2. However, the company warns that it may take up to 48 hours before the patch becomes available to all affected devices.
For users still on Windows 10, Microsoft has stopped free security updates as of this month. Those wishing to continue receiving patches must now purchase the Extended Security Updates (ESU) package, available through the Microsoft Store, which extends support until 2026.
As The Register summed up: “Within the same week, Microsoft’s installer broke, its new OS borked local development, and its multimillion-dollar upgrade campaign instead highlighted how fragile its ecosystem still is.”
