2026-09 Security update (KB5129195) (26200.9457) fails to download

Question

2026-09 Security update (KB5129195) (26200.9457) fails to download

noordkaap 45

2026-09 Security update (KB5129195) (26200.9457) fails to download
It downloads to 4% or 9% and then stops with the message that the security update has failed to download.
Have restarted my laptop several times and this problem keeps continueing for 3 days now.
How can I resolve this problem?

0 comments

Answer accepted by question author

Jose Benjamin Solis Nolasco 12,696 Volunteer Moderator

Welcome to Microsoft Q&A,

@noordkaap I hope you are doing well,

KB5129195 is a September 2026 out-of-band update for Windows 11 24H2/25H2, so first confirm your Windows version by running winver.

Since the download repeatedly stops at 4–9%, I recommend resetting the Windows Update cache:

Open Command Prompt as Administrator.

Run:

net stop bits
net stop wuauserv
ren %systemroot%\SoftwareDistribution SoftwareDistribution.bak
ren %systemroot%\System32\catroot2 catroot2.bak
net start bits
net start wuauserv

Restart the PC.

Go to Settings > Windows Update > Check for updates and try KB5129195 again.

Microsoft documents this procedure for Windows Update download/update failures.

Also run the built-in Windows Update troubleshooter from Settings > System > Troubleshoot > Other troubleshooters > Windows Update.

If it still fails, please provide:

Windows version/build from winver

The exact Windows Update error code

Whether the device is managed by WSUS, Intune, or another update-management solution

Those details will help determine whether this is a local Windows Update component issue or an update-management/configuration issue.

References:

https://support.microsoft.com/en-us/windows/troubleshoot-problems-updating-windows

https://support.microsoft.com/en-us/windows/windows-update-troubleshooter-19bc41ca-ad72-ae67-af3c-89ce169755dd

If this answer helped clarify the platform capabilities and save you troubleshooting time, please consider marking it as Accepted. This helps others in the community find similar solutions.

noordkaap 45 Reputation points

2026-09-23T03:47:59.9333333+00:00

Thank you for your reply. I hope you are doing well. I had tried Windows Update troubleshooter from **Settings > System > Troubleshoot > Other troubleshooters > Windows Update
Unfortunately that didn't work.
**However, it seems that by now Microsoft has solved the problem as I have been able to install the security update in the normal manner. Thanks again for your help.

Greetings,
noordkaap

Answer accepted by question author

Christine Luna 27,360 Independent Advisor

Greetings!

I'm Christine, I'll be happy to assist you. Sorry to hear that you're unable to install Windows updates. No worries, I'll do my best to help you.

Have you tried to run the Troubleshooter already?

Do you have 3rd party antivirus? (Please try to temporarily disable it before running the Windows update)

Please follow the steps below:

Windows Update Troubleshooter

Windows 11

Please Click Start menu and type Troubleshoot

Hit Other troubleshooters

And select Windows Update

Finally, Run the troubleshooter

Please check if the issue persists

Please click Start menu and type CMD, right click on it and choose Run as Admin, please paste the command below and hit enter.

DISM.exe /Online /Cleanup-image /Scanhealth

DISM.exe /Online /Cleanup-image /Restorehealth

Please wait for it to finish and repair the system files.

Once done, please paste the command below and hit enter.

sfc /scannow

Please wait to finish.

Check if the issue persists.

Reset Windows update services:

Please click start menu and type cmd, right click on it and choose run with admin

Kindly copy and paste the command lines below and hit enter:

net stop wuauserv

net stop cryptSvc

net stop bits

net stop msiserver

Ren C:\Windows\SoftwareDistribution SoftwareDistribution.old

Ren C:\Windows\System32\catroot2 Catroot2.old

net start wuauserv

net start cryptSvc

net start bits

net start msiserver

Please check if the issue persists.

Please try to perform an in place upgrade. In place upgrade will install the new features or updates of Windows it will also fix corrupted system files. Kindly check the steps below:

Video on how to perform in place upgrade:

https://www.youtube.com/watch?v=CAOwN68AInE&feature=youtu.be

Please go to https://www.microsoft.com/en-us/software-download/windows11

Look for Download Windows 11 Disk Image and select Windows 11 (multi-edition ISO)

Once you're able to download the ISO, please right click and open it
Please look setup.exe and run it
Select yes if you will will be asked for User Control
Choose Next to Continue
Please read the License Agreement and once done, hit Accept
Please wait until the setup program is done and it will check if your device space is enough for the update
You will see the Ready to install page, please ensure that the Keep personal files and apps has been checked.
Lastly, click INSTALL and follow the prompt.
It will restart your device several times, please wait for it to finish.

This may take sometime depends on your connection or the performance of your device.

Please let me know the result. I'll be happy to assist you all the way until it's resolved.

Thank you,

Christine L

Standard Disclaimer: Youtube.com link is a non-Microsoft website. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.

noordkaap 45 Reputation points

2026-09-23T03:56:04.4566667+00:00

Hello Christine,

Thank you for your reply. I don't use a third party antivirus. I had tried Windows Update troubleshooter from **Settings > System > Troubleshoot > Other troubleshooters > Windows Update Unfortunately that didn't work. However, it seems that by now Microsoft has solved the problem as I have been able to install the security update in the normal manner. Thanks again for your help.

Greetings, noordkaap
Christine Luna 27,360 Reputation points Independent Advisor

2026-09-23T07:21:34.8966667+00:00

Oh thank you for updating me. Appreciated. I'm glad that you're able to install the update. Have a good one and stay safe!

Regards,

Tin

3 additional answers

Your answer

noordkaap 45 Reputation points

2026-09-23T03:47:59.9333333+00:00

Thank you for your reply. I hope you are doing well. I had tried Windows Update troubleshooter from **Settings > System > Troubleshoot > Other troubleshooters > Windows Update
Unfortunately that didn't work.
**However, it seems that by now Microsoft has solved the problem as I have been able to install the security update in the normal manner. Thanks again for your help.

Greetings,
noordkaap
noordkaap 45 Reputation points

2026-09-23T03:56:04.4566667+00:00

Hello Christine,

Thank you for your reply. I don't use a third party antivirus. I had tried Windows Update troubleshooter from **Settings > System > Troubleshoot > Other troubleshooters > Windows Update Unfortunately that didn't work. However, it seems that by now Microsoft has solved the problem as I have been able to install the security update in the normal manner. Thanks again for your help.

Greetings, noordkaap
Christine Luna 27,360 Reputation points Independent Advisor

2026-09-23T07:21:34.8966667+00:00

Oh thank you for updating me. Appreciated. I'm glad that you're able to install the update. Have a good one and stay safe!

Regards,

Tin

Answer 1

Try these steps in order:

Check for updates again
- Open Start > Settings > Windows Update.
- Select Check for updates.
- Make sure the laptop is connected to the internet while downloading.
Run the Windows Update troubleshooter
- Open Start > Settings > System > Troubleshoot > Other troubleshooters.
- Find Windows Update and select Run.
- Follow the on-screen steps, then restart and try the update again.
Manually install KB5129195
- Search for KB5129195 in the Microsoft Update Catalog.
- Download the package that matches the device architecture.
- For x64, this update may require the checkpoint cumulative update KB5043080 first.
- If installing manually one file at a time, install in this order:
  1. windows11.0-kb5043080-x64_953449672073f8fb99badb4cc6d5d7849b9c83e8.msu
  2. windows11.0-kb5129195-x64_ed361878ec2b56a7dfdb8f256565263a7fdc8eaa.msu
- If the checkpoint update is already installed, Windows will indicate that.
Install both MSU files together with DISM
- Put all downloaded MSU files for KB5129195 in the same folder, for example C:\Packages.
- Ensure no other files are in that folder.
- Open Command Prompt as administrator.
- Run:
```
     DISM /Online /Add-Package /PackagePath:c:\packages\windows11.0-kb5129195-x64_ed361878ec2b56a7dfdb8f256565263a7fdc8eaa.msu
```
- DISM scans the folder and installs any required checkpoint cumulative updates automatically.
If the problem continues
- After resolving the failed install, monitor Windows Update status.
- If it still fails, contact Microsoft Support and include relevant CBS.log data.

Note: manual package installation changes system update state. Use the package that matches the device architecture.

Answer 2

Simone Racine 0

I have the same issue on a brand new laptop

0 comments

Answer 3

Glenn M 0

I have a simular problem with this update on Win 11 Home laptop.

It fails on reboot with the message "Something didn't go as planned. No need to worry, undoing changes. Please keep your computer on".

I have tried to install this update true the windows update menu and manually download the update. Both ways give me the same problem.

Also tried this but didn't help:
DISM.exe /Online /Cleanup-image /Scanhealth
DISM.exe /Online /Cleanup-image /Restorehealth
sfc /scannow

noordkaap 45 Reputation points

2026-09-23T03:51:16.7433333+00:00

Thank you for your reply. It seems that by now Microsoft has solved the problem as I have been able to install the security update in the normal manner. I hope you have been able to install this security update as well.

Greetings, noordkaap