12

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.

Improve this question
8
  • See this post: stackoverflow.com/questions/79790827/… Uninstalling the latest updates seems to fix the issue for now. Commented yesterday
  • 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 yesterday
  • 5
    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 yesterday
  • 2
    It's definitely on-topic for testing updates before impacting production. 🫳🏻🎤 Commented yesterday
  • 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 yesterday

6 Answers 6

Reset to default
9

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

Improve this answer
2
  • 3
    I'd already uninstalled the first 2 with no effect. 5065789 was the one that fixed things when I removed it! Commented yesterday
  • 3
    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 yesterday
8

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.

Improve this answer
2
  • 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 23 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 16 hours ago
5

I can confirm that forcing an update of Windows Defender definitions resolves this problem (e.g. to 1.439.216.0 or higher):

https://www.microsoft.com/en-us/wdsi/defenderupdates

The TLDR; is force the definition updates from CMD as administrator:

cd %ProgramFiles%\Windows Defender MpCmdRun.exe -removedefinitions -dynamicsignatures MpCmdRun.exe -SignatureUpdate

Then reboot. It won't work until you have restarted.

Improve this answer
New contributor
Christopher Cook is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
1
  • 1
    Just downloading latest updates which should include the defender update as well should fix the problem on Windows 11. This did correct my issue using HTTP.sys so I expect it will correct the other uses broken by this update as well. Commented 4 hours ago
1

To fix this, in most cases it should be sufficient to install KB2267602 (should be in Windows Update if you force a check) and restart.

Improve this answer
New contributor
chrisjshields is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
1

I believe something did change with the Windows Update like everyone is saying, however, for me, I was able to fix this by selected the Debug Target for each of my Startup Projects. I think it was defaulting to IIS Express but maybe with the update it was using an older version or something. After manually selecting IIS Express as the debug target instead of selecting nothing, it began to work.

Improve this answer
New contributor
thenninger is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
1
  • Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. Commented 1 hour ago
-1

I had the same issue. I couldn't uninstall KB5066835 due to it being required by the OS. I did an in-place upgrade through Windows update after which I was able to uninstall KB5066835, allowing my local websites to load.

Improve this answer
1
  • As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. Commented 5 hours ago

You must log in to answer this question.