Patch tracker / KB5122876
KB5122876: Windows Server 2019 Security Update (September 2026)
KB5122876 is a Critical security update for Windows Server 2019, released 2026-09-08. It closes 616 CVEs with a maximum CVSS of 9.8. At least one of them is actively exploited (CISA KEV), so this is a deploy-first update. It is the fifth largest of the 69 updates Microsoft shipped that month, by CVEs closed.
Update summary
Fixes 616 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 9.8 (Critical). EPSS exploit probability up to 3.6%. Among the top half of tracked Microsoft updates by EPSS exploit probability.
Microsoft documents 1 known issue with this update.
- Remote Desktop Services might stop responding after September 2026 security update
Senserva AI Opinion and rich prompt for KB5122876
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5122876
- Released
- 2026-09-08
- Last changed
- 2026-09-24
- Changes tracked
- 4
Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.
Microsoft revised KB5122876 on 2026-09-12: CVEs fixed 615 to 616.
- 2026-09-12 CVEs fixed 615 to 616
Recorded by Senserva on the dates shown, from the MSRC release feed. This is what moved and when, which neither the vendor advisory nor NVD publishes.
Check if KB5122876 is installed
Elevated PowerShell. No output means it is not installed.
Known issues, from Microsoft
Quoted from Microsoft's support article for KB5122876 (checked 2026-09-27). Verify against the article before acting.
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.
Note
This issue does not affect Windows 365 or Azure Virtual Desktop.
Resolution
This issue is resolved in Windows updates released on and after September 14, 2026 such as KB5129238 . We recommend you install the latest Windows update for your device as it contains important improvements and issue resolutions, including this one.
Applies to: Windows 10 Enterprise LTSC 2019
This security update includes fixes and quality improvements that are part of the following update:
August 11, 2026—KB5120238 (OS Build 17763.9121)
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.
If you installed earlier updates, only the new updates contained in this package will be downloaded and installed on your device.
For more information about security vulnerabilities, see the Security Update Guide and September 2026 Security Updates .
For information about ...
Windows release health for this update
From Microsoft's Windows release health for Windows Server 2019 and Windows 10, version 1809, checked 2026-09-29. Microsoft's issue text is linked from each title.
Issues Microsoft traces to this update
- USB audio devices might fail to start or produce no sound
Mitigated. Microsoft last updated it 2026-09-29 10:12 PT. - Remote Desktop Services might stop responding after Sept. 2026 security update
Resolved by KB5129238. Microsoft last updated it 2026-09-17 19:22 PT.
CVEs fixed by this update
Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.
Scope and sources
- Affected products
- Also released in September 2026
KB5122871
679 CVEs · Critical · exploitedKB5122878
568 CVEs · Critical · exploitedKB5122880
602 CVEs · Critical · exploitedKB5122882
641 CVEs · Critical · exploitedKB5123065
393 CVEs · Critical · exploitedKB5123066
418 CVEs · Critical · exploitedKB5123099
555 CVEs · Critical · exploitedKB5124008
628 CVEs · Critical · exploitedThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.