KB5066835 update causing IIS Service to not work

Sashi Kumar 405

Recently my local hosted IIS services is not running after the new update. My visual studio projects also can't be run as well. I have to delete the new update in order to run my projects and local hosted services again. May I know what is the problem?

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aziz parpiyev 45 Reputation points

2025-10-15T12:50:23.85+00:00

C# Using HttpListener class, listening on address "http://localhost:XXXX/"; it was working fine before windows update, after update getting an error HttpListenerException: 50 / The request is not supported the Exception causes on line listener.GetContext();
adragon202 5 Reputation points

2025-10-15T20:04:16.35+00:00

My applications are using System.ServiceModel.ServiceHost for some local network communications and were knocked out by KB5066131. After I removed that they started working again.
dIeGoLi 5 Reputation points

2025-10-15T21:04:29.63+00:00

Also for me since KB5066835 is installed oauth login into my .net native app with authorization code delivery to localhost:port opened by with HttpListener does not work anymore.
Dharminder Shinh 0 Reputation points

2025-10-15T21:13:43.25+00:00

We are using IIS to host local sites and APIs as well as hosting a WCF service within a windows service and have this problem too. The connection is always refused for both IIS and WCF.

I cannot remove the update as it's not our hardware, they just use our software so if someone has a solution I would appreciate that as we now have 17 clients who cannot use our software anymore. I will be recommending removal of the update but it's not ideal.
MATHEW SCHLABAUGH 40 Reputation points

2025-10-15T22:30:52.74+00:00

I think my problem maybe the exact same as everyone else's here.

My IIS Express was not allowing connections. I was getting the ERR_HTTP2_PROTOCOL_ERROR on a curl request to my local IIS Express. That's strange because it worked yesterday and I changed nothing but doing some Windows Updates and shutting down my computer.

I figured it might have to do with the updates.

So I went online and managed to determine it was likely being caused by a Windows Update I recently installed.

2025-10 Cumulative Update for Windows 11, version 25H2 for x64-based Systems (KB5066835) (26200.6899)

I went into the Windows Update settings -> Update History (Scrolled To The Bottom) -> Uninstall Updates

I see the update listed.

I clicked "Uninstall" next to the update.

Restarted my machine.

Not working! Alright let's keep searching for a fix.

Things I tried that didn't work.

I found a registry hack so I tried that and restarted but it didn't work.

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HTTP\Parameters]

"EnableHttp2"=dword:00000000
"EnableHttp2Tls"=dword:00000000
"EnableHttp2Cleartext"=dword:00000000

I seen various scripts to remove the updates that might be causing it.

It had one I hadn't tried to remove yet.

It didn't show in the updates I had installed on my computer in Windows Update history. Weird?

I had already removed 5066835 so when I ran the next line it said it was not installed.

wusa /uninstall /kb:5066835

I don't like registry hacks so I removed the keys.

I ran:

wusa /uninstall /kb:5065789

It said the update didn't exist, but then it proceeded to uninstall something. Weird?!

Restarted the computer

Working!!! Yay!!!

Oops!!! I forgot to turn off automatic updates. I went into the Windows Update settings again and unchecked automatic updates.

Let's see if I manually check now. Does it know I uninstalled it?

If so maybe I can hide it or try to keep it from installing again.

It started installation again and it wouldn't let me cancel the update.

Restarted

Still working!!! Yay!!!

So now I have the update installed and it is working. Weird???
Sashi Kumar 405 Reputation points

2025-10-16T01:35:30.3+00:00

Kestrel version seems working fine. As temporary solution I planned to run this on localhost
FedericoEstudio 0 Reputation points

2025-10-16T03:10:25.1933333+00:00

I did restore the register, and it was worse. I have not yet recover from the problems it produces.
Marco Leite 0 Reputation points

2025-10-16T05:03:02.5+00:00
I have the same issue. Kept getting error "ERR_HTTP2_PROTOCOL_ERROR" while trying to access an app deployed in IIS.

Spent 6+ hours trying any other possible fix:

Removing the enforcement on TLS1.3 - Did not work.

Restoring administration.config file to various previous versions - Did not work

Towards the 6 hours GPT gave me some error messag that was starting to match my results:

use curl to test connection, for example: "curl -vk --resolve your.certificate.url:12345:127.0.0.1 https://your.certificate.url:12345/"

then use this command line to isolate the problem:

Get-ChildItem "C:\Windows\System32\LogFiles\HTTPERR" | Sort LastWriteTime -Desc | Select -First 1 | % { Get-Content $_.FullName -Tail 100 }
Look for a line containing port

My result was "Connection_Dropped"

Then GPT's suggestion was to create a brand new "sterile" site to compare results against my site.

The steps for this felt pretty intense, so I start to take the root of uninstalling updates.

Uninstalled KB5066835, KB5066131, KB068331 via command line (1 of them gave an error "update not installed")

Uninstalled KB5064401 and KB5065789 via the uninstall button in windows settings - Updates history

Every time with a restart and tests in between.

After removing KB5065789 and restarting, the app started working properly again.

So the problem is either on KB5065789 or multiple of these 5 updates

Hope this helps someone
Bogdan Cristian Razvan 10 Reputation points

2025-10-16T06:08:03.6933333+00:00

Great job, it's like pushing it directly to master, resolved by a system update without any update notice.
Roland Berghöfer 10 Reputation points

2025-10-16T09:06:15.29+00:00

Microsoft seems to have reacted very quickly and posted a new update file online.

I uninstalled KB5066835 on all affected computers at 1 a.m. today – which solved the problem.

I forgot to pause updates for the next few days on one computer. The computer reinstalled the update there. But that worked.

This morning, I reinstalled the update on all other computers, and everything is working perfectly again.

For once, Microsoft reacted very quickly here. I suspect because millions of customers were affected (IIS + HTTP listener).
Robert Lane 10 Reputation points

2025-10-16T10:30:42.2633333+00:00

Thank you so much, I wasted a whole day yesterday because of this shocker. None of the websites on my machine worked after a reboot and I just couldn't figure it out, uninstalling IIS, changing firewall settings, stopping AV etc. This morning I have uninstalled KB5065789 and I am back in business. Completely outrageous outage - Thanks Microsoft for yet another complete shambles.
Earl Dean 0 Reputation points

2025-10-16T15:22:37.76+00:00

I fixed this without removing updates KB5066835 cumulative win 11 and KB5066131 .net 3.5 and 4.8.1 by uninstalling and reinstalling IIS, .Net 3.5, and the ASP.Net developer runtime features from windows on the local intranet app server. This allowed the windows updates to stay in place.
RICARDO ANDRADE 0 Reputation points

2025-10-16T18:52:55.8566667+00:00

Hi Microsoft you need to add a new patch to fix all of this, after I removed the patch, all my solutions were working and my IIS now is working properly, is the only solution I saw it and applied to my computer
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Answer accepted by question author

xavier ubikos 175

Hi there!

This morning there was a Defender update, I have installed it an now it works!!!

Sashi Kumar 405 Reputation points

2025-10-16T06:40:25.8666667+00:00

The localhost is working after updating as well
Bhavik Pola 10 Reputation points

2025-10-16T06:55:20.24+00:00
Resolution Steps Taken

Uninstalling the update using the following command:

wusa /uninstall /kb:5066835

wusa /uninstall /kb:5066131

wusa /uninstall /kb:5065789

wusa /uninstall /kb:5064401

wusa /uninstall /kb:5065426

Restart the machine after uninstall.

Pausing Windows Updates for 5 weeks to prevent reinstallation.

100% fix this issue....
moyu Me 0 Reputation points

2025-10-16T06:58:14.0266667+00:00

Hey, How should I update? I didn't find any updates in Windows Update.
Sashi Kumar 405 Reputation points

2025-10-16T07:01:36.61+00:00

If don't have update probably your PC already downloaded and installed the update. Try to restart the PC and see
Diptesh Bagadia 10 Reputation points

2025-10-16T07:03:55.8366667+00:00
Resolution Steps Taken

Uninstalling the update using the following command:

wusa /uninstall /kb:5066835

wusa /uninstall /kb:5066131

wusa /uninstall /kb:5065789

wusa /uninstall /kb:5064401

wusa /uninstall /kb:5065426

Restart the machine after uninstall.

Pausing Windows Updates for 5 weeks to prevent reinstallation.

100% Working.
David Mangold 0 Reputation points

2025-10-16T07:57:52.7733333+00:00

For my part I didn’t see the update either.... I rebooted the PC but didn’t see it, and it wasn’t installed. Maybe the update is being rolled out later in some countries? My solution: I uninstalled update KB5066835 and now everything works again. I’ve paused Windows Update for 5 weeks and will check later if there’s an update that fixes this issue.
Jan van Rhijn 270 Reputation points

2025-10-16T08:08:45.95+00:00

I have installed the "Security Intelligence Update for Microsoft Defender Antivirus - KB2267602 (Version 1.439.210.0)" today and for me it is now working again!
AdamBarnsley-3186 6 Reputation points

2025-10-16T08:14:37.7166667+00:00

Installed the update and now working!
Savio Vincent Fernandes 15 Reputation points

2025-10-16T08:27:44.0866667+00:00
No need to roll back or disable updates

Repair the WCF Services installation by re-enabling all associated features. This process forces the system to properly reconfigure the affected components without requiring a full rollback of the Windows update.

Open the Control Panel. You can do this by searching for "Control Panel" in the Start Menu.

Navigate to Programs > Programs and Features.

Click on Turn Windows features on or off in the left-hand menu.

In the list of features, scroll down and expand .NET Framework 4.8 Advanced Services.

Expand WCF Services.

Select all of the WCF Services by clicking the checkbox next to the parent "WCF Services" folder. If any are already checked, uncheck and then re-check them to ensure they are re-enabled.

Click OK to apply the changes.

You may be prompted to restart your computer. It is critical to do this restart for the changes to take effect and for the services to be properly re-registered.
JohnR 0 Reputation points

2025-10-16T09:09:01.79+00:00

Just tested that. I acknowledge that the Defender update resolved the issue
MK-5121 5 Reputation points

2025-10-16T09:19:02.57+00:00

Worked for me as well (wasn't able to remove updates before so this works without updating). For the ones who couldn't update online can download and install it from (I did like that):
https://www.microsoft.com/en-us/wdsi/defenderupdates

Just keep in mind, the file you downloaded seems like doing nothing. Just run it with admin privilages and wait couple of minutes and restart your pc. It should work.
Webprofusion 5 Reputation points

2025-10-16T10:18:43.34+00:00
To force Windows Defender updates, as per https://www.microsoft.com/en-us/wdsi/defenderupdates

From an Administrator CMD run the following to update definitions. You must reboot after for the fix to take effect:

cd %ProgramFiles%\Windows Defender MpCmdRun.exe -removedefinitions -dynamicsignatures MpCmdRun.exe -SignatureUpdate
Chris Clancy 10 Reputation points

2025-10-16T12:38:22.36+00:00

Don't uninstall anything at this point and turn back on windows updates. Originally uninstalling KB5066835 and KB5065789 resolved this - but we had dozens of machines unable to uninstall KB5065789 due to an error. Reinstalling KB5066835 later in the day on the machines with failed KB5065789 resolved the issue for us on ALL machines.

This is all dumb - and cost so many people wasted time...
Steven K 0 Reputation points

2025-10-16T13:41:35.79+00:00

I can confirm that this indeed corrects the problem. My use of HTTP.sys now functions normally with all windows/defender updates applied.
Danfer Habed 25 Reputation points

2025-10-16T14:15:13.6733333+00:00
Yeah! working now, in my case, using Windows 11, went to:

Windows Security, Virus & threat protection, Virus & threat protection settings, updated to latest (last update 10/16/2025).

Back to settings, Windows Update, re-enable Get latest updates, updated, restarted.

Now IISExpress working and able to run localhost, thanks!
Felipe Xavier da Rocha 0 Reputation points

2025-10-16T14:31:51.5266667+00:00

Installing this Microsoft Defender Antivirus update - KB2267602 solved my problem
Angel Alcaide 0 Reputation points

2025-10-16T15:35:05.9333333+00:00

In my case, I uninstalled IIS Express from Windows applications. I restarted my computer. And I downloaded and installed the latest version from Microsoft's page. It worked perfectly.
Ryan Johnson 10 Reputation points

2025-10-16T17:21:47.2333333+00:00

We're seeing that many machines automatically got the defender update, and we just need to reboot them, after which all is working again.
Shawn Nix 5 Reputation points

2025-10-16T20:44:38.1366667+00:00

Some of our devs were having this issue yesterday along with other staff using applications that relied on the .net httplistener. Not all staff with the KB5066835 update ran into those issues though. Just some staff oddly enough. So we paused pushing the updates to anyone else.

Then this morning all the staff who had issues reported in that their apps started working again after a reboot. We made no changes on our end so were very confused.

Then I saw this answer about updating Defender and that could explain what we were seeing. If a combination of the KB5066835 and a specific Windows Defender update was the cause of the issue or if Microsoft placed a patch in a Defender update this morning. Then that could be the resolution for some users.

I suggest making sure you are on the latest Defender update and rebooting as one of your first trouble shooting steps before attempting to remove updates.
Tim 0 Reputation points

2025-10-23T23:15:32.8966667+00:00

Did this break again today? System installed Security Intelligence update for MS Defender KB2267602 and now the problem has resurfaced for me.
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50 additional answers

Daniel Madera Bazán 20 Reputation points

2025-10-15T12:17:13.86+00:00

Same problem, uninstalling the update KB5066835 solves it!
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5 people found this answer helpful.
Vivek Kumar 0 Reputation points

2025-10-15T19:18:20.1366667+00:00

Ruined my whole day with this unwanted issue, was unable to run localhost website neither from IIS nor via IIS Express(VS 2019,2022). Thanks for adding a post here.

Ray Han 0 Reputation points

2025-10-15T21:25:54.68+00:00

Same problem here, uninstalling the update KB5066835 or uninstalling the update KB5066835 and KB5065789 resolve it!

Bola Adekoya 0 Reputation points

2025-10-16T02:25:12.1566667+00:00

Same problem. After a lot of digging around. This thread https://serverfault.com/questions/1193405/http-2-protocol-error-connecting-to-localhost-web-sites led me here and voila, uninstalling the 2 updates (KB5066835 and KB5065789) solves the problem
John Hatton 25 Reputation points

2025-10-15T21:30:47.6+00:00

As someone pointed out, the problem is not just IIS, but anything opening a port using .net HTTPListener. Minimal reproduction : https://github.com/BloomBooks/httplistener-test
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4 people found this answer helpful.
Webprofusion 5 Reputation points

2025-10-16T03:20:40.7433333+00:00

Nice, didn't realize it affects .net 9 as well.
Ryan Johnson 10 Reputation points

2025-10-15T17:03:53.5566667+00:00

This has halted credit card processing for tens of thousands of our merchants this morning. Please, Microsoft, push an automatic fix in windows update! That's too many machines for us to uninstall those updates.
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Bogdan Cristian Razvan 10 Reputation points

2025-10-15T12:32:44.79+00:00
KB5066835 breaks WCF .svc endpoints (no custom headers/middleware involved)

After installing Windows 11 KB5066835 (24H2/25H2), plain WCF .svc endpoints stop working , even in a minimal setup with no custom headers, middleware, or reverse proxies. The same service works immediately after uninstalling the KB.Invoke-WebRequest http://localhost:9011/mysvc?wsdl -UseBasicParsing

Invoke-WebRequest : The underlying connection was closed: An unexpected error occurred on a receive.

At line:1 char:1
- Invoke-WebRequest http://localhost:9011/mysvc?wsdl -UseBasicPa ...
- + CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-WebRequest], WebException + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand
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2 people found this answer helpful.

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