Google’s October Windows 11 update breaks localhost

Numerous Windows 11 users are reporting that localhost has stopped working following the October security update KB5066835. The issue is being widely discussed across Microsoft Support, Stack Overflow, and Server Fault forums.

Localhost is a key tool for developers to test web apps and sites on local servers, and its failure has disrupted many development environments.

Microsoft has yet to officially acknowledge the problem, leaving users to troubleshoot it themselves. In most cases, uninstalling update KB5066835 resolves the issue, though some users report having to also roll back the September update, KB5065789.

Forum discussions suggest that the bug causes failures in HTTP/2 connections and frequent local disconnections. Further investigation points to the system driver HTTP.sys, responsible for handling HTTP traffic in Windows, as the likely source of the problem.

According to TechPowerUp, issues like this are becoming increasingly common in Windows 11. While updates patch security vulnerabilities, they often trigger new problems in other system components, particularly in developer environments that rely on local testing tools.