Windows 11 Update Broke LocalHost This Time

About this video

• Video Title: Windows 11 Update Broke LocalHost This Time
• Channel: ThioJoe
• Speakers: ThioJoe
• Duration: 00:04:45

Overview

This video explains a recent Windows 11 update (KB5066835) that inadvertently broke localhost connections, specifically those using HTTP/2. The presenter details the nature of the bug, how it affected users (particularly developers using Visual Studio), and provides the fix, which is a Known Issue Rollback. Additional potential fixes and a bonus tip on updating Windows Defender definitions are also covered.

Key takeaways

• Bug Introduction: A recent Windows 11 Patch Tuesday update, KB5066835 (build 26100.6899), temporarily broke localhost functionality for some users.
• Specific Impact: The issue primarily affected HTTP/2 connections, which are used by a newer version of the HTTP protocol. Developers using Visual Studio were among those who noticed errors like "Error Connection Reset" and "Error HTTP/2 Protocol Error."
• The Fix: Microsoft released a Known Issue Rollback that specifically targets and undoes the problematic part of the update without requiring a full uninstall. This can be obtained by running Windows Update and checking for updates.
• Alternative Solutions: Some users reported success by updating Windows Defender security definitions or by clearing the cache and re-updating them using specific commands from a Microsoft article.
• Underlying Mechanism: The rollback appears to work by modifying feature flags in the Windows registry, allowing Microsoft to disable specific problematic features without uninstalling the entire update.
• Bonus Tip: A shortcut can be created to immediately force Windows Defender to download the latest security definitions, which can sometimes help with issues related to unrecognized or blocked programs.