Patch tracker / KB5099539
KB5099539: Windows Server 2019 Security Update (July 2026)
KB5099539 is a Critical security update for Windows Server 2019, released 2026-07-14. It closes 314 CVEs with a maximum CVSS of 9.9. At least one of them is actively exploited (CISA KEV), so this is a deploy-first update. The most likely of them to be attacked is CVE-2026-42982, which FIRST.org rates at 64% probability of exploitation in the next 30 days.
Update summary
Fixes 314 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 9.9 (Critical). EPSS exploit probability up to 64%. Among the top 25% of tracked Microsoft updates by EPSS exploit probability.
A newer security update for Windows 10 Version 1809 for 32-bit Systems has shipped since this one: KB5094041 (2026-08-11). For cumulative update families the newer package includes these fixes, so installing that one is usually the shorter path. Verify against your own update rings before you skip this package.
Microsoft documents 1 known issue with this update.
- We are currently not aware of any issues with this update
KB5099539 is a July 2026 Patch Tuesday Security Update for Windows 10 versions 21H2 and 22H2 across 32-bit, x64, and ARM64 systems, and it addresses CVE-2026-50661, a publicly disclosed BitLocker zero-day. Because the flaw is in BitLocker, any of these Windows 10 devices relying on BitLocker for drive encryption, particularly laptops that can be physically accessed or stolen, are the ones most at risk. Per-update CVE detail is still provisional from the MSRC release document, but the public disclosure of the BitLocker issue raises the urgency for encrypted endpoints.
Do this: Deploy KB5099539 to your Windows 10 21H2 and 22H2 fleet now, starting with BitLocker-protected laptops and other physically exposed devices.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5099539
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5099539
- Released
- 2026-07-14
- Last changed
- 2026-07-29
- Changes tracked
- 3
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 KB5099539 on 2026-07-29: CVEs fixed 313 to 314.
- 2026-07-29 CVEs fixed 313 to 314
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 KB5099539 is installed
Elevated PowerShell. No output means it is not installed.
Known issues, from Microsoft
Quoted from Microsoft's support article for KB5099539 (checked 2026-08-11). Verify against the article before acting.
We are currently not aware of any issues with this update
Applies to: Windows 10 Enterprise LTSC 2021 and Windows 10 IoT Enterprise LTSC 2021
Important
Use EKB KB5003791 to update to Windows 10, version 21H2 on supported editions.
This security update includes fixes and quality improvements that are part of the following updates:
June 9,2026—KB5094127 (OS Builds 19045.7411 and 19044.7411)
The following is a summary of the issues that this update addresses when you install this update. If there are new features, it lists them as well. The bold text within the brackets indicates the item or area of the change we are documenting.
[OLE Automation (known issue)] Fixed: Addresses a compatibility issue in OLE Automation (oleaut32.dll) that was introduced by the June 2026 security update. Some applications that use the IDispatch::Invoke method to call COM methods with BYREF parameters that share the same underlying storage might fail. These failures can include parameter marshaling errors or automation call failures. This update corrects how parameter ownership is managed and restores expected application behavior.
[File Explorer (known issue)] Fixed: An issue where the OneDrive shortcut in File Explorer stops working when File Explorer is run with administrative mode.
[Recycle Bin (known issue)] Fixed: This update addresses an issue where the confirmation dialog might display an ...
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 July 2026
KB5099444
185 CVEs · Critical · exploitedKB5099445
174 CVEs · Critical · exploitedKB5099535
261 CVEs · Critical · exploitedKB5099536
389 CVEs · Critical · exploitedKB5099538
312 CVEs · Critical · exploitedKB5099540
326 CVEs · Critical · exploitedKB5101649
383 CVEs · Critical · exploitedKB5101650
380 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.