Microsoft documented a Windows 11 update problem that could stop IIS websites and other server-side applications using HTTP.sys from accepting incoming connections. For affected users, a site at http://localhost/ could fail with “Connection reset – error (ERR_CONNECTION_RESET).” It was a specific IIS/HTTP.sys fault—not evidence that Windows 11’s entire localhost or loopback support had stopped working.
What the Windows 11 localhost problem actually was
Microsoft said incoming connections to some server-side applications that rely on HTTP.sys could fail after particular updates. IIS websites were among the affected services, including sites hosted at http://localhost/. The documented symptom was that a site might not load and could show “Connection reset – error (ERR_CONNECTION_RESET).” Microsoft’s support notice describes the issue and its scope.
That does not mean every application using the hostname localhost stopped working. The documented failure concerned incoming connections to HTTP.sys-dependent server applications, including IIS. Microsoft’s notice does not establish that browsers universally failed to resolve localhost, that all loopback traffic broke, or that every development server and tool was affected.
Which Windows versions and updates were involved?
Microsoft identified Windows 11 versions 24H2 and 25H2 as affected. The named triggering updates were the September 2025 preview update KB5065789 and the October 14, 2025 security update KB5066835. Microsoft noted that environments could differ, so the issue was not necessarily experienced on every affected installation.
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Windows Server 2025 was not affected, according to the same Microsoft support notice. The problem should also not be confused with a separate Windows Recovery Environment issue involving USB keyboards and mice after KB5066835; Microsoft addressed that separate issue with KB5070773.
How Microsoft resolved the 25H2 issue
Microsoft’s Windows 11, version 25H2 resolved-issues record identifies KB5065789 as the originating update and KB5067036, released October 28, 2025, as the update that resolved the issue for 25H2.
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The incident is historical. Microsoft’s current Windows 11 25H2 known-issues page, current as of September 29, 2026, does not list the localhost/IIS problem among open issues. The cited resolution record specifically identifies 25H2; it should not be read as proof of a separately documented fix status for every possible 24H2 configuration.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.If localhost IIS is failing on your PC now
If you are seeing a similar connection-reset error today, first establish whether the failure matches this incident rather than assuming localhost itself is broken:
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- Check your Windows version and installed update history to see whether the system is running 24H2 or 25H2 and whether the relevant updates are present.
- Confirm that the failing site is hosted by IIS or another server-side application that depends on HTTP.sys. A failure in a different local development server is not, by itself, evidence of this documented issue.
- Compare the symptom with Microsoft’s documented error and consult its current release-health guidance for your Windows version.
The available Microsoft records establish the historical trigger and the 25H2 resolution, but they do not establish that uninstalling a security update is necessary or advisable for a similar problem now. Do not remove an update solely because a local site fails; verify the Windows build and current Microsoft guidance first.
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