On October 14, 2025, Microsoft released the data-analytics-id=”inline-link” href=”https://support.microsoft.com/en-gb/topic/october-14-2025-kb5066835-os-builds-26200-6899-and-26100-6899-1db237d8-9f3b-4218-9515-3e0a32729685″ data-url=”https://support.microsoft.com/en-gb/topic/october-14-2025-kb5066835-os-builds-26200-6899-and-26100-6899-1db237d8-9f3b-4218-9515-3e0a32729685″ target=”_blank” referrerpolicy=”no-referrer-when-downgrade” data-hl-processed=”none”>Windows 11 cumulative update KB5066835. It was intended to deliver security fixes and stability improvements, but instead introduced a serious problem. The update broke localhost functionality for many users, causing major disruption for developers who rely on local testing every day.
data-analytics-id=”inline-link” href=”https://www.techpowerup.com/341976/microsoft-breaks-localhost-with-windows-11-october-update-users-forced-to-revert” data-url=”https://www.techpowerup.com/341976/microsoft-breaks-localhost-with-windows-11-october-update-users-forced-to-revert” target=”_blank” referrerpolicy=”no-referrer-when-downgrade” data-hl-processed=”none”>Reported on by TechPowerUp, the update broke localhost connections, which use the 127.0.0.1 or localhost address and are essential for testing websites, apps, and APIs on a local…
