Flexis September 2026 Patch Recommendation
Patches Microsoft released in September 2026
KB5122871: – 2026-09 Cumulative Update for Microsoft server operating system version 24H2 for x64-based Systems
KB5122882: 2026-09 Cumulative Update for Microsoft Server operating system version 21H2 for x64-based Systems
KB5122876: 2026-09 Cumulative Update for Windows Server 2019 (1809) for x64-based Systems
KB5123099: 2026-09 Cumulative Update for Windows Server 2016 for x64-based Systems
KB5122874: 2026-09 Servicing Stack Update for Windows Server 2016 for x64-based Systems
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Microsoft Windows
Microsoft Edge
(HTML-based)
Microsoft Edge
(Chromium-based)
Internet Explorer
Microsoft Office and Microsoft Office Services and Web Apps
Windows Defender
Visual Studio
ASP.NET Core
Chakra Core
Microsoft Dynamics
.NET Framework
.NET Core
Please note the following information regarding the security updates:
Windows 10 Enterprise and Education and Windows 10 Home and Pro Lifecycle pages, Windows 10 was ended on October 14, 2025. The current version, 22H2, will be the final version of Windows 10. The following editions will remain in support with monthly security update releases through that date:
Home
Pro
Pro Education
Pro for Workstations
Education
Enterprise
Enterprise multi-session
KB5122871: Windows Server 2025, all editions
Windows Secure Boot certificate expiration
Important: Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. Microsoft has been updating these certificates on consumer and non-managed business devices over the past several months. Devices that haven’t received the newer certificates will continue to start and operate normally, and standard Windows updates will continue to install. Updated certificates will continue to be delivered through Windows Update in the coming months.
Improvements
This security update contains fixes and quality improvements from KB5120233 (released August 11, 2026). The following summary outlines key issues addressed by this update. Also, included are available new features. The bold text within the brackets indicates the item or area of the change.
- [Certificates] This update improves application compatibility during Windows certificate-authority updates, helping applications continue to work as expected as Microsoft transitions to newer signing certificates
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco’s transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Networking] This update improves network failover on Windows Server systems by helping connections respond more quickly when a network adapter is disconnected. This helps network storage and file access continue to work as expected.
- [Remote Desktop] This update improves Remote Desktop audio redirection, helping audio from remote sessions play correctly on the local device.
- [Sysmon]
- This update improves Sysmon’s Process Tampering detection by preventing false Event ID 25 alerts for normal Windows Session Manager (smss.exe) activity.
- This update improves Sysmon reliability during file monitoring, helping prevent unexpected system crashes when archive directories are unavailable.
- This update improves Sysmon tampering detection by making executable file validation more reliable and consistent.
- This update improves Sysmon file archiving reliability, helping monitored file operations complete as expected even when archive directories cannot be accessed.
Known issues in this update
Windows Server Update Services (WSUS) does not display error details
Symptoms
After installing KB5070881 or later updates, Windows Server Update Services (WSUS) does not display synchronization error details within its error reporting. This functionality is temporarily removed to address the Remote Code Execution Vulnerability, CVE-2025-59287.
Remote Desktop Services might stop responding after September 2026 security update.
Symptoms
After installing the September 2026 Windows security update, some organizations might experience issues with Remote Desktop Services (RDS).
In some environments, RDS might become unstable, resulting in RDP connections failing after several minutes, sign-in issues, or servers hanging at “Please wait for the Remote Desktop Configuration”. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, and File Explorer might also become unresponsive. Additionally, the Windows Update page might stop responding and continuously display a loading indicator.
KB5122882: Windows Server 2022
Improvements
This security update contains fixes and quality improvements from KB5120242 (released August 11, 2026). The following summary outlines key issues addressed by this update. Also, included are available new features. The bold text within the brackets indicates the item or area of the change.
- [Certificates] This update improves application compatibility during Windows certificate-authority updates, helping applications continue to work as expected as Microsoft transitions to newer signing certificates.
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco’s transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Hyper-V] This update addresses an issue that might cause a limited number of Windows Server 2022 virtual machines to intermittently encounter a stop error 0x139 resulting in an unexpected restart.
- [Networking] This update improves network failover on Windows Server systems by helping connections respond more quickly when a network adapter is disconnected. This helps network storage and file access continue to work as expected.
- [Remote desktop] This update improves Remote Desktop audio redirection, helping audio from remote sessions play correctly on the local device.
Known issues in this update
Windows Server Update Services (WSUS) does not display error details
Symptoms
- After installing KB5070884 or later updates, Windows Server Update Services (WSUS) does not display synchronization error details within its error reporting. This functionality is temporarily removed to address the Remote Code Execution Vulnerability, CVE-2025-59287.
Remote Desktop Services might stop responding after September 2026 security update
Symptoms
After installing the September 2026 Windows security update, some organizations might experience issues with Remote Desktop Services (RDS).
In some environments, RDS might become unstable, resulting in RDP connections failing after several minutes, sign-in issues, or servers hanging at “Please wait for the Remote Desktop Configuration”. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, and File Explorer might also become unresponsive. Additionally, the Windows Update page might stop responding and continuously display a loading indicator.
KB5122876: Windows Server 2019 Win 10 Ent LTSC 2019
Windows Server 2019
Applies to: Windows Server 2019
This security update includes fixes and quality improvements that are part of the following update:
The following is a summary of the issues that this update addresses when you install this update. The bold text within the brackets indicates the item or area of the change we are documenting.
- [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Certificate deployment via Windows updates continues across supported PCs and non-managed business devices in the coming months.
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco’s transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Windows Code Integrity policies] Improves application compatibility during Windows certificate-authority rotation by recognizing Microsoft Windows Production PCA 2026 RSA2048-SHA256 as equivalent to PCA 2011.
- [Remote Desktop] This update addresses an issue that affects Remote Desktop audio redirection. Audio from the remote session might not play on the local computer in certain configurations.
Windows 10, Version 1809
Applies to: Windows 10 Enterprise LTSC 2019
This security update includes fixes and quality improvements that are part of the following update:
This security update includes fixes and quality improvements that are part of the following update:
The following is a summary of the issues that this update addresses when you install this update. The bold text within the brackets indicates the item or area of the change we are documenting.
- [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Certificate deployment via Windows updates continues across supported PCs and non-managed business devices in the coming months.
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco’s transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Windows Code Integrity policies] Improves application compatibility during Windows certificate-authority rotation by recognizing Microsoft Windows Production PCA 2026 RSA2048-SHA256 as equivalent to PCA 2011.
- [Remote Desktop] This update addresses an issue that affects Remote Desktop audio redirection. Audio from the remote session might not play on the local computer in certain configurations.
Known issues in this update
Remote Desktop Services might stop responding after September 2026 security update
Symptoms
After installing the September 2026 Windows security update, some organizations might experience issues with Remote Desktop Services (RDS).
In some environments, RDS might become unstable, resulting in RDP connections failing after several minutes, sign-in issues, or servers hanging at “Please wait for the Remote Desktop Configuration”. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, and File Explorer might also become unresponsive. Additionally, the Windows Update page might stop responding and continuously display a loading indicator.
KB5123099: Windows Server 2016, all editions Win 10 Ent LTSB 2016 Win 10 IoT Ent LTSB 2016
Summary
Windows Server 2016
Applies to: Windows Server 2016
This security update includes fixes and improvements that are a part of the following update:
The following is a summary of the issues that this update addresses. The bold text within the brackets indicates the item or area of the change we are documenting.
- [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Certificate deployment via Windows updates continues across supported PCs and non-managed business devices in the coming months.
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco’s transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Windows Code Integrity policies] Improves application compatibility during Windows certificate-authority rotation by recognizing Microsoft Windows Production PCA 2026 RSA2048-SHA256 as equivalent to PCA 2011.
- [Remote Desktop] This update addresses an issue that affects Remote Desktop audio redirection. Audio from the remote session might not play on the local computer in certain configurations.
- [Microsoft Compatibility Telemetry service (known issue)] Fixed: After installing Windows update KB5120418 released on August 11, 2026, some Windows Server 2016 devices might generate recurring Application Error events (Event ID 1000, with exception code 0xc0000409) associated with CompatTelRunner.exe.
Known issues in this update
Remote Desktop Services might stop responding after September 2026 security update.
Symptoms
After installing the September 2026 Windows security update, some organizations might experience issues with Remote Desktop Services (RDS).
In some environments, RDS might become unstable, resulting in RDP connections failing after several minutes, sign-in issues, or servers hanging at “Please wait for the Remote Desktop Configuration”. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, and File Explorer might also become unresponsive. Additionally, the Windows Update page might stop responding and continuously display a loading indicator.
Microsoft Support: IT administrators who need an immediate workaround should contact Microsoft Support for Business for assistance.
Resolution
Microsoft is working to address this issue in a future Windows update and will provide additional details when available.
Windows 10 Version 1607
Applies to: Windows 10 Enterprise LTSB 2016 and Windows 10 IoT Enterprise 2016 LTSB
- This security update includes fixes and improvements that are a part of the following update:
The following is a summary of the issues that this update addresses. The bold text within the brackets indicates the item or area of the change we are documenting.
- [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Certificate deployment via Windows updates continues across supported PCs and non-managed business devices in the coming months.
- [Date and Time] This update adjusts Morocco Standard Time to reflect Morocco’s transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.
- [Windows Code Integrity policies] Improves application compatibility during Windows certificate-authority rotation by recognizing Microsoft Windows Production PCA 2026 RSA2048-SHA256 as equivalent to PCA 2011.
- [Remote Desktop] This update addresses an issue that affects Remote Desktop audio redirection. Audio from the remote session might not play on the local computer in certain configurations.
Known issues in this update
Remote Desktop Services might stop responding after September 2026 security update
Symptoms
After installing the September 2026 Windows security update, some organizations might experience issues with Remote Desktop Services (RDS).
In some environments, RDS might become unstable, resulting in RDP connections failing after several minutes, sign-in issues, or servers hanging at “Please wait for the Remote Desktop Configuration”. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, and File Explorer might also become unresponsive. Additionally, the Windows Update page might stop responding and continuously display a loading indicator.
Microsoft Support: IT administrators who need an immediate workaround should contact Microsoft Support for Business for assistance.
Resolution
Microsoft is working to address this issue in a future Windows update and will provide additional details when available.
KB5122874: Win 10 Ent LTSB 2016 Win 10 IoT Ent LTSB 2016 Windows Server 2016, all editions
Important
Free support for Windows 10 Enterprise 2016 LTSB and Windows Server 2016 will soon end. For information about the availability of Extended Security Updates (ESUs), see the End of support section.
Summary
This servicing stack update (SSU) makes quality improvements to the servicing stack, which is the component that installs Windows updates. Servicing stack updates make sure that you have a robust and reliable servicing stack so that your devices can receive and install Microsoft updates.
Important
Not installing the latest SSU before applying Windows updates might result in the Windows update not being offered until the latest SSU is installed.