A critical October 2025 update, KB5066835, for Windows 11 (versions 24H2 and 25H2) has disrupted numerous development environments by disabling the localhost loopback, a key feature for developers. This update followed the September preview, KB5065789, aimed at addressing security vulnerabilities. However, developers reported unexpected issues particularly affecting ASP.NET and Visual Studio tools.
Details of the Disruption
Multiple developers experienced failures in their local development setups due to the broken localhost loopback. This issue has hindered access to local web applications and services crucial for development work. Microsoft identified the problem arising from conditions such as internet connectivity and the timing of update installations and restarts.
- Update affected Windows 11 (versions 24H2 and 25H2).
- Developers face disruptions with ASP.NET and Visual Studio.
- Mitigations involve uninstalling KB5066835 or disabling specific services.
- Problem linked to conditions including internet connectivity and timing.
Mitigations and Future Steps
Some users have found temporary workarounds such as uninstalling KB5066835 or pausing further updates. Others removed the previous preview update, KB5065789, or disabled services like Hyper-V, IIS, Windows Process Activation Service, and .NET Framework 3.5/4.8. Microsoft plans to address these issues using Known Issue Rollback and aims to release a resolution in an upcoming update.
Security and IT experts caution against rolling back security patches due to the vulnerabilities it could introduce. They recommend better quality assurance processes, testing updates in controlled environments, and preparing rollback strategies to manage such disruptions effectively.
