KB5065426 Failures: How to Fix the Windows 11 September Update and Restore Network Sharing

Microsoft’s September 2024 cumulative update for Windows 11 24H2, KB5065426, is failing to install for a significant number of users, spawning a confusing array of error codes and, in some cases, breaking network file sharing after it does apply. If you’re staring at a persistent “update failed” message or your shared folders suddenly refuse credentials, you need a clear path forward – and you need it now.

A Rocky Patch Tuesday: What’s Failing

Released as part of the regular Patch Tuesday cadence, KB5065426 bumps Windows 11 to OS Build 26100.6584 and bundles both an updated servicing stack (SSU) and the monthly cumulative fix (LCU). This fat package delivers scores of security patches and quality improvements, but for many machines the installer never completes.

PCWorld and Windows Latest have aggregated the error codes users see most often:

Users also report that manual installation via the Microsoft Update Catalog, normally a reliable workaround for flaky Windows Update, gags at the same point. The standalone .msu file progresses to roughly halfway and then quits without a helpful message.

Making matters more urgent: KB5065426 is mandatory. Once published, Windows Update repeatedly tries to download and install it, so a failing machine enters an endless loop of notifications and reboots unless you intervene.

An Unwanted Bonus: Broken SMB and Network Credentials

Even those who successfully installed the patch are not out of the woods. Several independent forums and community threads describe a sudden inability to access shared folders, mapped drives, or NAS devices. The most telling symptom is “System error 86 – the specified network password is not correct,” even when credentials haven’t changed. It appears the update interferes with how Windows 11 handles saved SMB credentials, although Microsoft has not yet confirmed a direct link beyond a documented known issue for PowerShell Direct in hotpatched virtualized environments.

Who’s Affected – and How It Feels

The impact breaks down along user type:

• Home users face a repeated, annoying failure that can hog bandwidth and trigger unwanted restarts. If file sharing is used for a home NAS or shared family folder, the SMB glitch can instantly cut off access to photos, backups, or media.
• Power users and small-office workers who rely on network shares for file collaboration are disconnecting from essential resources. Some have found that clearing saved credentials or remapping drives with explicit IP addresses works around the issue, but it’s a frustrating band-aid.
• IT administrators inherit both installation puzzle and post-update regression. The combined SSU+LCU packaging means the usual wusa /uninstall trick won’t remove the servicing stack, so rollback requires DISM commands. Testing the update on a limited pilot ring is essential before approving it for the whole fleet.

Why This Update Is So Problematic

Three technical factors combine to make KB5065426 more trouble than a typical monthly patch:

1. Bulky SSU+LCU combo. Because the update carries its own servicing stack, it alters the fundamental Windows Update plumbing while also applying the cumulative payload. If anything goes wrong in the SSU phase, the entire install collapses, and the usual uninstall pathways are partly blocked.
2. Wide-ranging changes. The package touches core networking components, security mitigations, and the servicing store. A single misstep in any subsystem can yield a different error code, which is why we see so many.
3. Environment sensitivity. Machines with third-party security suites, non-standard drivers, or customized SMB settings are more likely to hit a fence. The incomplete install state can leave the component store corrupted, making subsequent retries even harder.

Your Action Plan: Fixes and Workarounds

Don’t panic. Multiple repair paths are working for people right now. Start with the quick, low-risk steps and escalate if needed.

For Home Users and Solo Pros

1. Pause updates to stop the retry loop
- Go to Settings > Windows Update > Pause updates and select a pause duration. This won’t fix anything, but it gives you breathing room to apply a real repair without constant failed install attempts.

2. Repair system files and the component store
- Open an elevated Command Prompt and run:
sfc /scannow
Wait for the scan to finish, then run:
DISM /Online /Cleanup-Image /RestoreHealth
This checks and fixes corruptions that may be blocking the installer. Reboot afterward.

3. Reset the Windows Update cache
- Stop the update services (elevated Command Prompt):
net stop wuauserv net stop cryptSvc net stop bits net stop msiserver
- Rename the cache folders:
rename C:\Windows\SoftwareDistribution SoftwareDistribution.old rename C:\Windows\System32\catroot2 catroot2.old
- Restart services:
net start wuauserv net start cryptSvc net start bits net start msiserver
Reboot and check Windows Update again. This clears any corrupt download files.

4. Use the Media Creation Tool for an in-place upgrade
If Windows Update still chokes, this is your most reliable fallback. It re-installs Windows while keeping your personal files and apps.
- Download the Media Creation Tool from Microsoft’s Windows 11 download page.
- Run it as administrator and choose “Upgrade this PC now”.
- Select “Keep personal files and apps” when prompted.
- Let the tool complete the upgrade. When it finishes, you’ll be on the latest build with KB5065426 integrated.

5. Try the Windows Update Assistant
An alternative to the Media Creation Tool, the Update Assistant also forces a build upgrade and often bypasses the broken pipeline. Download it from the same official page and follow the prompts.

6. If SMB access is broken, reset network credentials
- Open the Control Panel and go to Credential Manager > Windows Credentials.
- Remove any stored credentials that reference the problematic server or NAS.
- Reboot and re-enter your username and password when reconnecting to the share, or try mapping the drive using the server’s IP address instead of its name.

For IT Administrators and Managed Environments

• Block the update until tested. Use Update Ring policies in Configuration Manager or Windows Update for Business to defer KB5065426. Confirm it doesn’t break your line-of-business apps or networking in a pilot group.
• Prepare a rollback plan. Because the servicing stack is bundled, removal requires DISM:
  DISM /Online /Get-Packages | findstr KB5065426 DISM /Online /Remove-Package /PackageName:Package_for_KB5065426~...
  Replace the package name with the exact string from the first command. Test this on a non-production machine first.
• Script post‑installation checks. After deploying the update, automatically verify SMB share connectivity, core service status, and event logs for errors. A quick PS script can catch the credential bug before users complain.
• Keep an offline recovery image. Combined packages raise the stakes for a broken OS. Maintain a current backup so you can restore a machine quickly if the update corrupts the operating system.

What to Watch Next

Microsoft has not issued a broad “known issue” for the installation failures yet, but the volume of reports typically prompts two responses: either a revised package pushed via Windows Update, or a separate hotfix that patches the installer logic. Subscribe to the Windows Release Health dashboard and keep an eye on the official KB5065426 support page (linked below). In the meantime, if the Media Creation Tool route works for you, you’ll already have the security fixes in place. For everyone else, pausing updates and staying vigilant is the smart play.