KB5087538 is the cumulative update for Windows Server 2019 and Windows Server 2019 Server Core installation. It was released on 12 May, 2026 under the ‘Patch Tuesday’ release cycle.
Salient points
- KB5087538 supersedes April 2026 cumulative update KB5082123.
- KB5087538 corresponds to Windows server build 17763.8755.
- KB5087538 also includes all changes that are part of the out of band update KB5091573 released on 19 April 2026.
- No Zero-day vulnerabilities affect Windows Server 2019 and Windows Server 2019 Server Core installation as per May security bulletin.
- 54 security vulnerabilities have been disclosed for May 2026 by Microsoft. Four of these have CRITICAL severity.
- The Servicing Stack Update corresponding to KB5087538 is KB5089760 (17763.8754). It is in-built in the main cumulative update. Separate installation of the SSU or Servicing Stack is not needed.
- KB5005112 is the SSU that must be already deployed on Windows Server 2019. If you have not deployed this SSU, please download KB5005112 and apply on the server. This is a very old SSU released in August 2021. If you have followed the update release cycle, there is a high chance that you already have this patch on the server. SSU installation does not cause server reboot.
Important Reminders
Apart from this, it is important to note that the Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. Secure Boot is a security feature in Unified Extensible Firmware Interface (UEFI) based firmware that helps ensure that only trusted software runs during a device’s boot (start) sequence.
Since Windows introduced Secure Boot support, all Windows-based devices have carried the same set of Microsoft certificates in the KEK and DB. These original certificates are nearing their expiration date, and your device is affected if it has any of the listed certificate versions. To continue running Windows and receiving regular updates for your Secure Boot configuration, you will need to update these certificates.
Download KB5089760
KB5089760 is the Servicing Stack Update for Windows Server 2019 released in April 2026 alongside the main cumulative update KB5082123.
If you intend to deploy cumulative updates through Windows Update or Windows Update for Business, no action is needed to install the Servicing Stack Update. The Servicing Stack Update is part of the security update that will be installed on Windows Server 2019.
For manual installation of KB5087538, there is no separate installation of KB5089760 as it is included in the main cumulative security update.
Download KB5087538
You may download the offline installer file for KB5087538 from the catalog site link shared below:
Upon installation of KB5087538, the server would restart. The Servicing Stack Update is already included in the main update and will be downloaded and installed as part of the installation process.
Zero-day vulnerabilities
No zero-day vulnerability has been reported for Windows Server 2019 in April 2026.
Critical vulnerabilities
The May security bulletin for Windows Server 2019 reports 54 security vulnerabilities. There are four CRITICAL vulnerabilities that affect Windows Server 2019.
| Vulnerability | CVSS | Impact | Comments |
|---|---|---|---|
| CVE-2026-32161 | 7.5 | Remote Code Execution | Concurrent execution using shared resource with improper synchronization (‘race condition’) in Windows Native WiFi Miniport Driver allows an unauthorized attacker to execute code over an adjacent network. |
| CVE-2026-35421 | 7.8 | Remote Code Execution | Heap-based buffer overflow in Windows GDI allows an unauthorized attacker to execute code locally. |
| CVE-2026-40403 | 8.8 | Remote Code Execution | Heap-based buffer overflow in Windows Win32K – GRFX allows an authorized attacker to execute code locally. |
| CVE-2026-41089 | 9.8 | Remote Code Execution | Stack-based buffer overflow in Windows Netlogon allows an unauthorized attacker to execute code over a network. |
Changelog – KB5087538
The following changes or improvements are part of KB5082123 for Windows Server 2019:
- The update addresses security improvements for Windows Server 2019 and Windows Server 2019 Server Core installation.
- [Internal Windows OS] This update contains miscellaneous security improvements to internal Windows OS functionality.
- [Remote Desktop security warnings (known issue)] Fixed: The Remote Desktop Connection security warning dialog might render incorrectly in multi-monitor configurations with different display scaling settings. This issue might occur after installing the Windows security update released on or after April 14, 2026 (such as KB5082123).
- [Secure Boot]
- This update enables dynamic status reporting for Secure Boot states in Windows Security App.
- With this update, Windows quality updates include additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Devices receive the new certificates only after demonstrating sufficient successful update signals, maintaining a controlled and phased rollout.
- [Sign-In] Fixed: After you install the Windows update released on or after March 10, 2026, some users might experience an issue signing in to apps with a Microsoft account. Even when the device has a working Internet connection, a “no Internet” error appears during sign in and prevents access to Microsoft services and apps such as Microsoft Teams.
- [Daylight Savings Time] Update for Arab Republic of Egypt to support the government DST change order in 2023.
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