Flexis September 2025 Patch Recommendation
Patches Microsoft released in September 2025
- KB5065426: 2025-09 Cumulative Update for Microsoft server operating system 24H2 for x64-based Systems
- KB5065432: 2025-09 Cumulative Update for Microsoft server operating system version 21H2 for x64-based Systems
- KB5065428:2025-09 Cumulative Update for Windows Server 2019 (1809) for x64-based Systems
Impacted Products:
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 will reach end of support 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
KB5065426: Windows 11 version 24H2, all editions
Windows Secure Boot certificate expiration
Important: Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. This might affect the ability of certain personal and business devices to boot securely if not updated in time. To avoid disruption, we recommend reviewing the guidance and taking action to update certificates in advance. For details and preparation steps,
Improvements
This security update contains fixes and quality improvements from KB5064081 (released August 29, 2025). 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.
[App compatibility (known issue)] Fixed: Addresses an issue that caused non-admin users to receive unexpected User Account Control (UAC) prompts when MSI installers perform certain custom actions. These actions might include configuration or repair operations in the foreground or background, during the initial installation of an application.
This issue could prevent non-admin users from running apps that perform MSI repairs, including Office Professional Plus 2010 and multiple applications from Autodesk (including AutoCAD). This fix reduces the scope for requiring UAC prompts for MSI repairs and enables IT admins to disable UAC prompts for specific apps by adding them to an allowlist.
[File server] This update enabled auditing SMB client compatibility for SMB Server signing as well as SMB Server EPA. This allows customers to assess their environment and identify any potential device or software incompatibility issues before deploying the hardening measures that are already supported by SMB Server. For detailed guidance, see CVE-2025-55234.
Known issues in this update
Symptoms
We are aware of an edge case affecting hotpatched devices that have installed the September 2025 Hotpatch update (KB5065474) or the September 2025 security update (KB5065426). These devices might experience failures with PowerShell Direct (PSDirect) connections when the host and guest virtual machines (VMs) are both not fully updated.
When a patched guest VM attempts to connect to an unpatched host (or vice versa), the system is expected to fall back to a legacy handshake and clean up the socket gracefully. However, this fallback mechanism fails intermittently, resulting in socket cleanup issues. The connection failure might appear random, and users might observe Event ID 4625 logged in the Security Event log within Windows Event Viewer.
Workaround
This issue is addressed in KB5066360. If your hotpatched device is experiencing issues with PSDirect connection, we recommend updating both the host and guest VM with these updates.
KB5065432: Windows Server 2022
Windows Secure Boot certificate expiration
Important: Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. This might affect the ability of certain personal and business devices to boot securely if not updated in time. To avoid disruption, we recommend reviewing the guidance and taking action to update certificates in advance. For details and preparation steps, see Windows Secure Boot certificate expiration and CA updates.
Improvements
This security update contains fixes and quality improvements from KB5063880 (released August 12, 2025). 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.
[App compatibility (known issue)] Fixed: Addresses an issue that caused non-admin users to receive unexpected User Account Control (UAC) prompts when MSI installers perform certain custom actions. These actions might include configuration or repair operations in the foreground or background, during the initial installation of an application.
This issue could prevent non-admin users from running apps that perform MSI repairs, including Office Professional Plus 2010 and multiple applications from Autodesk (including AutoCAD). This fix reduces the scope for requiring UAC prompts for MSI repairs and enables IT admins to disable UAC prompts for specific apps by adding them to an allowlist.
For more information, see Unexpected UAC prompts when running MSI repair operations after installing the August 2025 Windows security update.
[File server] This update enabled auditing SMB client compatibility for SMB Server signing as well as SMB Server EPA. This allows customers to assess their environment and identify any potential device or software incompatibility issues before deploying the hardening measures that are already supported by SMB Server. For detailed guidance, see CVE-2025-55234.
[Input] Fixed: This update addresses an issue with the Chinese (Simplified) Input Method Editor (IME) where some extended characters appeared as empty boxes.
[Performance] Fixed: This update addresses an issue where a single, oversized Certificate Revocation List (CRL) file slows down system performance. To improve speed and privacy, the system now plans to use smaller, partitioned CRLs.
Known issues in this update
Symptoms
We are aware of an edge case affecting hot patched devices that have installed the September 2025 Hot patch update (KB5065306) or the September 2025 security update (KB5065432). These devices may experience failures with PowerShell Direct (PSDirect) connections when the host and guest virtual machines (VMs) are both not fully updated.
When a patched guest VM attempts to connect to an unpatched host (or vice versa), the system is expected to fall back to a legacy handshake and clean up the socket gracefully. However, this fallback mechanism fails intermittently, resulting in socket cleanup issues. The connection failure might appear random, and users might observe Event ID 4625 logged in the Security Event log within Windows Event Viewer.
Workaround
This issue is addressed in KB5066359. If your hot patched device is experiencing issues with PSDirect connection, we recommend updating both the host and guest VM with these updates.
KB5065428: Windows 10 Enterprise, version 1809 Windows Server 2019
Support for Windows 10 will end in October 2025
After October 14, 2025, Microsoft will no longer provide free software updates from Windows Update, technical assistance, or security fixes for Windows 10. Your PC will still work, but we recommend moving to Windows 11.
Summary
Applies to: Win 10 Ent LTSC 2019, Win 10 IoT Ent LTSC 2019, and Windows 10 IoT Core LTSC
This security update includes fixes and quality improvements that are part of the following update:
August 12, 2025—KB5063877 (OS Build 17763.7678)
August 19, 2025—KB5066187 (OS Build 17763.7683) Out-of-band
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.
[Input and Composition] Fixed: An issue with the Chinese Simplified Input Method Editor (IME). Some extended characters were showing as empty boxes.
[App compatibility (known issue)] Fixed: Addresses an issue that caused non-admin users to receive unexpected User Account Control (UAC) prompts when MSI installers perform certain custom actions. These actions might include configuration or repair operations in the foreground or background, during the initial installation of an application.
This issue could prevent non-admin users from running apps that perform MSI repairs, including Office Professional Plus 2010 and multiple applications from Autodesk (including AutoCAD). This fix reduces the scope for requiring UAC prompts for MSI repairs and enables IT admins to disable UAC prompts for specific apps by adding them to an allowlist. For more information, see Unexpected UAC prompts when running MSI repair operations after installing the August 2025 Windows security update.
[File Server] New! This update enables auditing SMB client compatibility for SMB Server signing as well as SMB Server EPA. This allows customers to assess their environment and identify any potential device or software incompatibility issues before deploying the hardening measures that are already supported by SMB Server. For detailed guidance, see CVE-2025-55234 | Windows SMB Elevation of Privilege Vulnerability.