Windows 11 emergency patch fixes localhost and WinRE issues

Microsoft released a mandatory Windows 11 security update on October 14 that disrupted local networking and recovery functions on many PCs, prompting the company to issue an out-of-band emergency patch days later. The original update, KB5066835, interfered with localhost connections used by locally hosted applications and rendered the Windows Recovery Environment unresponsive to USB mice and keyboards on affected systems. Microsoft has said it is deploying an emergency update, KB5070773, which is rolling out via Windows Update for Windows 11 versions 24H2 and 25H2.

Analysis of the underlying fault points to a regression in the kernel-mode HTTP server component HTTP.sys. When a browser or application attempted to communicate with services on 127.0.0.1 using HTTP/2, HTTP.sys mishandled the HTTP/2 handshake frames and reset connections, preventing local servers and developer tools that rely on IIS or the ASP.NET Core module from responding. In addition to localhost failures, users reported installation errors and peripherals becoming inoperable, including certain USB mice and keyboards in the recovery environment.

Microsoft acknowledged the issues and advised affected users to...