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Need the proven secret to instantly repair the awful Windows Server 2025 IIS bug?
A recent Windows update in October 2025 created a significant problem for some users. The update, called KB5066835, stopped certain applications from working correctly on computers running Windows 11 and Windows Server 2025. Microsoft has since corrected this issue.
Understanding the Problem
The faulty update broke a core Windows feature known as the Internet Information Server (IIS). Many programs use IIS to communicate with the computer they are running on, a process that often uses the address localhost. When the update broke IIS, it was like cutting a phone line inside your computer. Applications trying to use localhost would fail, often showing an error message like “ERR_CONNECTION_RESET.”
This issue affected a wide range of important software, including:
- Customer Relationship Management (CRM) systems.
- Specialized accounting programs.
- Access management tools.
Essentially, any application that needed to host a website or service on the local machine stopped working. Microsoft acknowledged this problem on October 16, 2025, and initially offered a temporary solution for IT administrators called a Known Issue Rollback (KIR).
The Permanent Solution
On October 28, 2025, Microsoft announced a permanent fix for the IIS and localhost bug. You no longer need the temporary KIR solution. The correction is included in the Windows Preview Update KB5067036, which was released on the same day.
To fix the issue, you simply need to install this update or any subsequent Windows update. This will repair the connection problems and allow your applications to function normally again.
- Affected Systems: Windows 11 (versions 24H2 and 25H2) and Windows Server 2025.
- The Cause: The October 14 cumulative update (KB5066835) contained a bug.
- The Fix: Install the Windows Preview Update KB5067036 (from October 28) or any newer update.