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When connecting to a localhost web site using Visual Studio 2022 Community Edition, I receive the error:

This site can’t be reached The webpage at site.x.localhost might be temporarily down or may have moved permanently to a new web address.

ERR_HTTP2_PROTOCOL_ERROR

This occurred after installing:

  1. 2025-10-14 Cumulative Update for Windows 11 25H2 KB5066835 (26200.6899)

  2. Security Update for Microsoft ASP.NET MVC 5.1 (KB2994397) 2025-10

  3. Cumulative Update for .NET Framework 3.5 and 4.8.1 for Windows 11, version 25H2 for x64 (KB5066128)

  4. 2025-10 .NET 9.0.10 Security Update for x64 Client (KB5068332)

The error also occurs on website hosted in local IIS.

Before these updates, everything was working.

Has anyone else faced this issue?

I did a rollback, but it isn't working.

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Pratik V Shah is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
6
  • I asked the same question at micorosft learn. We have the same issues and it is really impacting our business learn.microsoft.com/en-us/answers/questions/5585563/… Commented 15 hours ago
  • 4
    To close voters, note that this update applies to both client workstations and Server OS versions of Windows (support.microsoft.com/en-us/topic/…). That makes it on-topic on Server Fault, in my opinion. Commented 14 hours ago
  • 2
    It's definitely on-topic for testing updates before impacting production. 🫳🏻🎤 Commented 13 hours ago
  • 1
    This appears to be a problem with anything that uses HTTP.sys, which is a windows kernel level approach to simplify deployment of a HTTP(s) endpoint. Hoping for a fix soon as it also impacts Microsoft IIS. Commented 11 hours ago
  • Note, in an addendum to my own comment, that while a server OS-specific version of this KB exists (as I linked in said comment), this question appears to be about the client OS-specific version, thus marking this question as an end user scenario rather than a server management one. Thus, this question should probably be migrated to Superuser, if a duplicate question does not already exist there. Commented 8 hours ago

4 Answers 4

Reset to default
7

I have tried on two of my production computers:

first uninstall KB5066835

Then KB5065789

That seemed to get it working again.

Edit:

Found this microsoft post:

microsoft

For me it was not releated to IIS (I don't use that), just a visual studio project (framework 4.8) that creates a websocket, which can not be connected to anymore since the update.

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keno is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
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  • I had to run a net stop was between the first and second uninstall to get the second uninstall to run. There may be another dependency in another service that might also block the uninstall, but this is what worked for me. Commented 10 hours ago
  • In my own snapshot testing, installing KB5066131, then restarting, caused the issue to appear. It could be that update rolls up things that are in other updates or vice-versa. community.certifytheweb.com/t/… Commented 3 hours ago
5

win + r => type "cmd" => ctrl,shift + enter (administrator cmd)

  • wusa /uninstall /kb:5066835

restart computer

  • wusa /uninstall /kb:5066131

restart computer

  • wusa /uninstall /kb:5065789

restart computer

  • rolling back from latest Visual Studio update

solved the issue for me

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tutte2k is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
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  • 1
    I'd already uninstalled the first 2 with no effect. 5065789 was the one that fixed things when I removed it! Commented 15 hours ago
  • 1
    And a heads up to anyone whose Windows will not allow you to uninstall the updates. I needed to uninstall Windows Sandbox before it allowed me to. Commented 11 hours ago
-1

Yes, exact same issue, i uninstalled all the individual updates from last night so not sure which one caused the issue but my vs is working again now. From what i have seen, most users are saying it was KB5066835

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-3

See this post: https://stackoverflow.com/questions/79790827/localhost-applications-failing-after-installing-2025-10-cumulative-update-for-wi

Uninstalling the latest updates seems to fix the issue for now.

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Marc Selman is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
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  • This doesn't really provide a solution, just a link to elsewhere. What updates are you referring to by "the latest updates", specifically? Commented 11 hours ago

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