Microsoft has released Windows 10 KB5122878 as part of the September 2026 security updates. The cumulative update is available for Windows 10 version 22H2 and version 21H2 and includes security fixes, quality improvements, and several changes affecting Secure Boot, Remote Desktop, BitLocker, Windows certificate handling, and date and time settings. This month’s release focuses on keeping supported Windows 10 systems secure and improving compatibility and reliability.
After installing KB5122878, Windows 10 version 22H2 moves to OS Build 19045.7725, while Windows 10 version 21H2 moves to OS Build 19044.7725. Since standard Windows 10 22H2 support ended in October 2025, KB5122878 is intended for eligible ESU devices and supported Windows 10 Enterprise LTSC and IoT Enterprise LTSC editions.
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What’s New in Windows 10 KB5122878?
KB5122878 does not bring any major new features to Windows 10. Instead, the September update focuses on security, compatibility, and reliability improvements. Microsoft has also addressed several specific issues affecting Secure Boot, Remote Desktop, BitLocker, certificate handling, and time-zone information.
Here are the most important changes and fixes included in the update.
| Item | Details |
|---|---|
| Update | KB5122878 |
| Release Date | September 08, 2026 |
| OS Build | 19045.7725 (22H2), 19044.7725 (21H2) |
| Update Type | Cumulative Security Update |
| Available For | Windows 10 22H2 ESU and supported 21H2/LTSC editions |
| Servicing Stack Update | KB5122877 is included with the cumulative update |
September 2026 Security Updates Patch Hundreds of Vulnerabilities
Security is an important part of the September 2026 Windows updates. Microsoft addressed 964 CVEs across its products this month, including 104 Critical and 860 Important vulnerabilities. The fixes cover a wide range of Microsoft products and Windows components, including Windows Update, Windows Kernel, Windows Remote Desktop Services, Windows DNS, Windows Imaging Component, Windows Hello, and other system components.
More importantly, Microsoft’s September security release fixes two actively exploited zero-day vulnerabilities. These are particularly worth noting because attackers were already exploiting them before the September updates were released.
- CVE-2026-81963: Windows Update Stack Elevation of Privilege vulnerability. An attacker who is already authorized to access the system could exploit the flaw to gain SYSTEM-level privileges.
- CVE-2026-85880: Windows Advanced Local Procedure Call (ALPC) Elevation of Privilege vulnerability. The flaw involves a heap-based buffer overflow and can also allow an authorized attacker to elevate privileges locally.
Microsoft recommends installing the applicable September security updates to address these vulnerabilities. For Windows 10 users, KB5122878 is included in this month’s security update. Microsoft also notes that the update includes the security and quality improvements delivered through the cumulative update.
1. Secure Boot Certificate Updates Reach More Devices
One of the more important changes in KB5122878 involves Secure Boot certificates.
Microsoft has been updating Secure Boot certificates because certificates used by many Windows devices began reaching expiration in 2026. KB5122878 adds more high-confidence device targeting data so Windows Update can identify additional systems that are eligible to automatically receive the newer Secure Boot certificates.
Microsoft says certificate deployment will continue through Windows updates for supported PCs and non-managed business devices over the coming months.
This is important because Secure Boot helps prevent unauthorized software from loading during Windows startup.
2. Windows 10 Gets a Morocco Time Zone Update
KB5122878 also updates Windows 10’s handling of Morocco Standard Time. Microsoft is changing its time zone behavior to reflect Morocco’s transition to permanent UTC+00:00 starting September 20, 2026.
The change is designed to ensure that Windows displays the correct local time after the transition. For most Windows 10 users outside Morocco, this change will have little or no noticeable effect.
3. Better OMA DM Client Logging
Microsoft has improved the logging capabilities of the OMA DM Client, which is the component used for Open Mobile Alliance Device Management.
The update allows the omadmclient.exe component to save more debugging information when it connects to a management server.
This change is primarily useful in managed and enterprise environments, where administrators need additional information when troubleshooting device management problems.
4. Improved Windows Certificate Compatibility
KB5122878 also includes an important change to Windows Code Integrity policies.
Microsoft says Windows now recognizes Microsoft Windows Production PCA 2026 RSA2048-SHA256 as equivalent to PCA 2011 during certificate-authority rotation.
The change is intended to improve application compatibility while Microsoft transitions to newer certificate authorities. For most home users, this should happen in the background, no need to perform any manual action.
5. Remote Desktop Audio Problem Fixed
The update addresses a problem affecting Remote Desktop audio redirection. In certain configurations, audio from a Remote Desktop session might not play through the local computer. KB5122878 fixes this issue.
This can be particularly relevant for people who use Remote Desktop to connect to another Windows computer for work or administration. If Remote Desktop audio was previously not working correctly, installing the September update may resolve the problem.
6. BitLocker Recovery Key Issue Addressed
Microsoft has also addressed an issue involving BitLocker Group Policy settings.
Under an unrecommended BitLocker Group Policy configuration, some devices could be required to enter their BitLocker recovery key.
KB5122878 addresses this problem. If you use BitLocker, it is still important to make sure your recovery key is safely backed up. Windows updates should not be treated as a substitute for having access to your recovery key.
Known Issues
At the time of writing, Microsoft has not reported any widespread new issues specifically introduced by KB5122878. Users should continue to monitor Microsoft’s release health dashboard for any emerging problems after installation.
How to install Windows 10 KB5122878
The update is available to devices enrolled in the ESU program, which has been extended through October 12, 2027, as well as Windows 10 Enterprise LTSC 2021 and IoT Enterprise LTSC 2021 systems.
To install it manually, follow these steps:
- Open Settings by pressing Windows + I.
- Go to Update & Security > Windows Update.
- Click Check for updates.
- If the update is available, you’ll see 2026-09 Cumulative Update for Windows 10 Version 22H2 (KB5122878).
- Click Download and install, then wait for Windows to complete the installation.
- Restart your PC when prompted to apply the update.
Ensure your device is connected to a stable internet connection to download update files from Microsoft’s servers. Once done, reboot your computer to apply the changes.
Download Windows 10 KB5122878 Manually
Alternatively, you can download the standalone installer directly from the Microsoft Update Catalog by searching for “KB5122878.”
Windows 10 KB5122878 Direct download links 64-bit and 32-bit (x86).
- Locate the patch next to the correct operating system edition and version.
- To install the update, simply run the downloaded MSU file and Windows will automatically install the cumulative update.
- If you are looking for the latest Windows 10 version 22H2 ISO, click here.
- In addition, you can download the latest Windows 11 ISO images here.
Frequently Asked Questions
Yes. Windows 10 reached end of support in October 2025. Monthly cumulative updates such as KB5122878 are available only to devices enrolled in the Extended Security Updates (ESU) program.
No. KB5122878 does not introduce major new Windows 10 features. It focuses on security fixes, reliability improvements, File History, Secure Boot certificate deployment, and servicing improvements.
Yes, generally via the standard Windows Update channel for eligible systems. It may also be available via Microsoft Update Catalog for manual download.
Microsoft has not committed to an open-ended ESU timeline for Windows 10. It is a transitional program.
The original Secure Boot certificates issued in 2011 are approaching expiration. Microsoft is replacing them with newer certificates to ensure systems continue booting securely in the future.
Also read:
- Difference Between Windows 10 Feature Updates and Cumulative Updates
- Windows Update won’t download or fails to install on Windows 10 (Solved)
- How to Share Files and Printers Between Two Windows 10 Computers
- Windows 10 keeps shutting down and restarting automatically. Try these solutions
- Complete Review of Microsoft Windows 10 Operating System
