Win Update KB5066835 Windows 11 Cumulative Update build 26100.6899 (24H2) and 26200.6899 (25H2) - Oct. 14

Coolmistry · Oct 17, 2025

itsme1 said:
I think it's the KB itself.

I've tried at least seven times.

Edit:
I'll check tomorrow too.

I tried resetting Windows Update with the bat file in this forum's tutorial, but it didn't work because the cryptsvc service failed to stop.

Yeah, me too got problem with Cryptsvc service failed then gave up and reset fresh Windows 11 24H2 and download latest Update Windows so far, all fixed and 100% healthy!

imanub · Oct 17, 2025

antspants said:
You are most probably right, Brian.
The most tedious is waiting for the direct download updated ISO.

pietcorus2 said:
15H2 Repair version ?...............never heard of , where (??) to get it...............?

I believe the user FrankW is referring to the new in-place upgrade/repair feature that Microsoft added to Windows 11 (Fix problems using Windows Update)

You can find it right within the system settings:

Open Settings (Win + I).
Go to System.
Select Recovery.
Look for the option: "Fix problems using Windows Update" and click "Reinstall now."

This is the fastest and safest way to perform a repair installation on the latest Windows versions without needing an ISO file or USB media."

cereberus · Oct 17, 2025

imanub said:
I believe the user FrankW is referring to the new in-place upgrade/repair feature that Microsoft added to Windows 11 (Fix problems using Windows Update)

You can find it right within the system settings:

Open Settings (Win + I).

Go to System.

Select Recovery.

Look for the option: "Fix problems using Windows Update" and click "Reinstall now."

This is the fastest and safest way to perform a repair installation on the latest - Windows versions without needing an ISO file or USB media."

Just tried it - much slower than just downloading iso and running setup.exe - took 15 mins to download files but I can download iso in 4 minutes.

Also took a long time to install but did work in the end.

To be fair, easier way of doing a repair; for lesser experienced persons who are not familiar with using isos.

Steve C · Oct 17, 2025

One PC on 24H2 failed this update at 100% then rolled back. I installed 25H2 OK on the PC and the same thing happened with the 25H2 update. Is this a buggy update? Have paused updates for a month to see what happens.

RJARRRPCGP · Oct 17, 2025

Steve C said:
One PC on 24H2 failed this update at 100% then rolled back. I installed 25H2 OK on the PC and the same thing happened with the 25H2 update. Is this a buggy update? Have paused updates for a month to see what happens.

Try a router reset.

Shad · Oct 17, 2025

Just confirming MCT will download 6899 ISO. I reinstalled via the ISO on USB yesterday. After the setup the OS version was 6899 before any updates from Windows Updates started.

Shad · Oct 17, 2025

Steve C said:
One PC on 24H2 failed this update at 100% then rolled back. I installed 25H2 OK on the PC and the same thing happened with the 25H2 update. Is this a buggy update? Have paused updates for a month to see what happens.

The update appears to have some issues for some, not for others. I have been looking at how the Sept MCT (which really has a version from August) setups Windows. From what I have seen on my own system is the Windows installation/update process has issues with the Sept updates being installed correctly regardless of what Winver displays. I dug through Event Viewer logs to find Windows Update Client fails on the Sept update and never successfully installs it but will change enough of the OS to make either the OS or Windows update determine the OS was updated correctly.

Grab MCT from the MS site, run it and select the ISO version. This will download 6899 version bypassing the previous version issues. At least from what I have seen on my own system. Use Rufus to setup the ISO on a USB and reinstall or use it for an in-place repair

itsme1 · Oct 17, 2025

Please note that since yesterday, this KB5066835 has been merged with the 25h2 enablement package via Windows Update. If you haven't installed the 25h2 enablement package with the MSU package and also this KB5066835, you will only have the merged 25h2 enablement package offered via Windows Update. And since KB5066835 gives errors on some computers, you will also get errors on the merged 25h2 enablement package.

If you have errors, you will need to install the 25h2 MSU enablement package. When you install it and run a Windows Update search, KB5066835 will be offered.

I experienced this yesterday on my computers.

Edit: To install the 25h2 enablement .msu package:
How to get the Windows 11 2025 version 25H2 Update

waltc · Oct 17, 2025

gunrunnerjohn said:
Maybe you should check again. This is the released version. The reason we forgot was because it was never true! I applied this to three computers, NONE of them are in the Insider program!

It's the release version in the Insider's Preview channel--and it will be eclipsed soon by another beta, as is the rule for all of the insider's channels. And actually, I had no trouble at all with it, as there is no telling what third-party stuff people decided to install and run on the previous preview release-channel betas, which has zero to do with the current release from Microsoft, even though people enjoy imagining that it is the fault of the latest Windows release exclusively. That was the point of my original comments.

waltc · Oct 17, 2025

Rollback_Jockey said:
This is the release, not beta, check the thread title.

Correct, and it installed perfectly first time out on my AM5 system. It did fail on my wife's AM4 system, twice, before using the "Fix Windows problems using Windows Update" option was applied, finally installing 26100.6899, and after that, the 26200.6899 version (the final commercial version) --25H2--installed as an upgrade right over the previous 24H2 6899 installation, in ~3 minutes. I detailed the situation in an earlier post in this thread for those who might be interested.

RJARRRPCGP · Oct 17, 2025

It installed perfectly on my AM4 system as well, even after having component store issues with the August and September patch-Tuesday updates.

I did a clean install on July 8th, due to my June 10th 24H2 installation getting borked with the July patch-Tuesday.

cereberus · Oct 17, 2025

Just been looking at the command (setdefaultuserfolder.cmd) in the dev version 26220.6772 that allows a user to override MS's naming of usernames if using an MS account with your own input username. It looks pretty basic and does not have any dependencies.

The key line is simply writing a regedit where %input% is the name you enter.

So I wondered if it is possible to copy the command into c:\windows\system32\oobe folder for the release version of 25H2 but I suspect there is probably hard coding later on that processes the input data, so even if we do update the registry, it may just get ignored.

However, I thought it was worth a try in case the required hard coding to use a custom username was already in 26200.6899.

Unfortunately, even though I copied the file in and executed it ok, it did nothing, and it still used the first five letters of my email address

.

key line

Code:

reg add HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\UserOOBE /v SetSAMFolderName /t REG_SZ /d "%input%" /f >nul

full code

Code:

@echo off
setlocal enabledelayedexpansion
chcp 65001 >nul

set "input=%*"

if "%input%"=="" (
    echo Usage: SetDefaultUserFolder.cmd ^<value^>
    echo Example: SetDefaultUserFolder.cmd MyFolderName
    exit /b 1
)

:: Now call PowerShell for detailed Unicode and reserved name validation
powershell -NoProfile -Command ^
    "$name = '%input%'.Trim();" ^
    "$invalid = [System.IO.Path]::GetInvalidFileNameChars() + @('@', '.', ';', '=', ',', '+');" ^
    "if ([string]::IsNullOrWhiteSpace($name)) { Write-Host '[ERROR] Name is empty or whitespace.'; exit 1 }" ^
    "elseif ($name.Length -gt 16) { Write-Host '[ERROR] Name exceeds 16 character limit.'; exit 2 }" ^
    "elseif ($name.EndsWith(' ') -or $name.EndsWith('.')) { Write-Host '[ERROR] Name cannot end with space or dot.'; exit 1 }" ^
    "elseif ('CON','PRN','AUX','NUL','COM1','COM2','COM3','COM4','COM5','COM6','COM7','COM8','COM9','LPT1','LPT2','LPT3','LPT4','LPT5','LPT6','LPT7','LPT8','LPT9' -contains $name.ToUpper()) { Write-Host \"[ERROR] '$name' is a reserved name.\"; exit 1 }" ^
    "elseif ($invalidChar = $name.ToCharArray() | Where-Object { $invalid -contains $_ } | Select-Object -First 1) { Write-Host \"[ERROR] Invalid character found in name: '$invalidChar'\"; exit 1 }" ^
    "else { Write-Host \"[OK] '$name' is a valid folder name.\" }"

if errorlevel 1 (
    echo [ERROR] Folder name validation failed in PowerShell.
    exit /b 4
)

:: Write to registry
reg add HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\UserOOBE /v SetSAMFolderName /t REG_SZ /d "%input%" /f >nul
if %errorlevel% EQU 0 (
    echo [SUCCESS] Default user folder set to: %input%
) else (
    echo [ERROR] Failed to set registry value. %errorlevel%
    exit /b 5
)

exit /b 0

Smalltown · Oct 17, 2025

25H2 was offered here today. Everything went ok.
SFC ran clean.

drminer · Oct 17, 2025

I successfully replaced winre.wim in the hidden recovery partition, using the version extracted from a downloaded Windows 11 ISO. But I may have modified the permissions in doing so. Does anyone know the default owner and permissions of the file? Copilot has given me three different answers to that question! Thanks.

FrancoDT · Oct 17, 2025

Just some FYI:

Microsoft confirmed that Windows 11 KB5066835 breaks localhost (127.0.0.1) HTTP/2 connections, which means locally hosted apps can no longer connect to your network, but that’s not the only problem. Windows 11 KB5066835 is causing the following issues for some users on version 24H2 or 25H2:

October 2025 Patch Tuesday won’t install due to 0x800f0922, 0x800f0983, 0x800f081f, 0x80071a2d and 0x800f0991. If you run into installation errors, we recommend downloading the patch from Update Catalog. Or just use Media Creation Tool and perform an in-place upgrade of 25H2. Don’t try your luck with internet solutions. They don’t work.
A bug blocks File Explorer document previews in the Preview pane, falsely citing a security issue.
Some Logitech peripherals won’t work.
Mouse and keyboard not working in WinRE (Windows Recovery Environment).

Microsoft confirms Windows 11 KB5066835 issues. Localhost, File Explorer preview, install errors

Windows 11 KB5066835 is causing the following issues: a bug that blocks lockhost connection, File Explorer preview pane and more.

www.windowslatest.com

FrankW · Oct 18, 2025

pietcorus2 said:
15H2 Repair version ?...............never heard of , where (??) to get it...............?

Fix issues by reinstalling the current version of Windows - Microsoft Support

Learn how to reinstall Windows using Windows Update.

support.microsoft.com

wowchick · Oct 18, 2025

cereberus said:
Just tried it - much slower than just downloading iso and running setup.exe - took 15 mins to download files but I can download iso in 4 minutes.

Also took a long time to install but did work in the end.

To be fair, easier way of doing a repair; for lesser experienced persons who are not familiar with using isos.

i just did the repair the other day that is faster

dbartenstein · Oct 18, 2025

drminer said:
I successfully replaced winre.wim in the hidden recovery partition, using the version extracted from a downloaded Windows 11 ISO. But I may have modified the permissions in doing so. Does anyone know the default owner and permissions of the file? Copilot has given me three different answers to that question! Thanks.

Copilot is very disingenuous.....

mta3006 · Oct 18, 2025

FrancoDT said:
Mouse and keyboard not working in WinRE (Windows Recovery Environment).

Microsoft confirms Windows 11 KB5066835 issues. Localhost, File Explorer preview, install errors

Windows 11 KB5066835 is causing the following issues: a bug that blocks lockhost connection, File Explorer preview pane and more.

www.windowslatest.com

Windowslatest.com proposes a fix for the WinRE/Advanced Startup problem. They say to disable WinRE with reagentc /disable, then replace c:\windows\system32\Recovery\winre.wim with a copy of winre.wim from the 25H2 ISO, then reenable WinRE with reagentc /enable.

How is this going to help if it was the latest update that broke WinRE?

itsme1 · Oct 18, 2025

mta3006 said:
Windowslatest.com proposes a fix for the WinRE/Advanced Startup problem. They say to disable WinRE with reagentc /disable, then replace c:\windows\system32\Recovery\winre.wim with a copy of winre.wim from the 25H2 ISO, then reenable WinRE with reagentc /enable.

How is this going to help if it was the latest update that broke WinRE?

This isn't a fix, it's a rollback.
Microsoft is going to release a real fix.

AI Component	Version
Image Search	1.2509.1022.0
Content Extraction	1.2509.1022.0
Semantic Analysis	1.2509.1022.0
Settings Model	1.2509.1022.0

Win Update KB5066835 Windows 11 Cumulative Update build 26100.6899 (24H2) and 26200.6899 (25H2) - Oct. 14

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October 14, 2025 - KB5066835 (OS Builds 26200.6899 and 26100.6899)

Highlights

Improvements

AI Components

Windows 11 servicing stack update (KB5067360)- 26100.6893

Known issues in this update

How to get this update