2026-09 Security Updates failures

Mazza 25 Reputation points
2026-09-16T20:27:06.38+00:00

2026-09 Security Update (KB5129195) (26200.9457) - Download error - 0x80070102 - Retrying won't fix this

2026-09 .NET Framework Security Update (KB5126052) - Installing - 99% - Retrying still won't install at all

I am just a user and have tried contacting Microsoft for a call back 2 days ago but no luck so any fix needs to be in easy to understand terms please - thanks

Windows for home | Windows 11 | Windows update
Answer accepted by question author

AI answer

2026-09-16T20:27:25.95+00:00

For a home Windows 11 device, the simplest supported first step is to use the built-in repair option for Windows Update:

  1. Open Settings.
  2. Go to System > Recovery.
  3. In Fix problems using Windows Update, select Reinstall now.
  4. Wait for it to finish.
    • This process is described as not affecting files, settings, or installed apps.
  5. After it completes, try Windows Update again.

If the update still fails, try this cleanup step before checking for updates again:

  1. Select Start and type cmd.
  2. Right-click Command Prompt and select Run as administrator.
  3. If prompted by User Account Control, select Yes.
  4. Run this command:
dism /online /cleanup-image /startcomponentcleanup
  1. Wait for the command to complete.
  2. Restart the PC.
  3. Go back to Windows Update and try again.

If KB5129195 continues to fail, it can also be installed manually from the Microsoft Update Catalog. For x64 systems, Microsoft lists these files in order:

  1. windows11.0-kb5043080-x64.msu
  2. windows11.0-kb5129195-x64.msu

Microsoft states that required checkpoint cumulative updates must be installed in order before the target cumulative update. Another supported method is to place the MSU files in the same folder and install the target package with DISM from an elevated Command Prompt:

DISM /Online /Add-Package /PackagePath:c:\packages\windows11.0-kb5129195-x64.msu

Important: manual package installation is more advanced than the built-in Reinstall now option, so the recovery option should be tried first.

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  1. Rastaman5 - 0 Reputation points
    2026-09-23T15:57:22.8033333+00:00

    I have been unable to install the last two (Sept 2026) Windows 11 malware updates. My well-equipped two-year old laptop now crashes 3-5x/day. In July-August it only crashed 1-2x/day. On average, I spend 16 hours/month preparing for (backing up) problems arising from forced microsoft updates, and troubleshooting programming errors interwoven throughout the windows 11 operating system and occurring in every OS update.

    This is severely affecting my ability to get anything done on my primary work computer. I just tried running the windows update troubleshooter, and it too failed to run. It is impossible to get any live help from microsoft to resolve the myriad problems with it's operating system. No other product I own requires the amount of time and attention to problem solving necessary just to keep it running.

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  2. John Jefferson Doyon 88,630 Reputation points Independent Advisor
    2026-09-16T22:20:08.14+00:00

    Hi, @Mazza

    To help narrow down the issue:

    1. May I know what other troubleshooting steps have you already taken? This will help me avoid recommending them again.
    2. Have you already checked whether you have any third-party antivirus software running?

    If you haven't tried anything yet please start by:

    First, make sure there's no third-party antivirus software active that might be interfering with the update process:

    • Open the Windows Security app.
    • Click the "Settings" (gear icon) in the lower left.
    • Under Security Providers, click "Manage Providers".
    • Verify if Microsoft Defender Antivirus is the active antivirus and Windows Firewall is the firewall.
    • If not, please uninstall the third-party antivirus, restart your PC, and check again at Settings > Windows Update.

    If issue persists, run again the Windows Update Troubleshooter from Get Help app:

    • Open Settings > System > Troubleshoot > Other troubleshooters.
    • Find Windows Update and click Run. This will open the Get Help app.
    • Select "I can't download, install, or uninstall an update" and click "Yes".
    • This will automatically identify and address any errors and restart the update process. This step is purely automatic.
    • Please continue to follow the prompt if the issue persists.

    If the issue persists, please provide more details by answering my questions.

    Click "Add comment" to let me know.

    Thanks!

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