KB5099539: Windows Server 2019 Security Update (July 2026)

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Download KB5099539

Get the official update for KB5099539. The download and file size for each supported product are on the Microsoft Update Catalog page.

Update summary

Senserva AI Opinion for KB5099539

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

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.

Exploitation and severity

Fixes 313 CVEs. Most severe CVSS 9.9 (Critical). EPSS exploit probability up to 3.2%.

Among the top half of tracked Microsoft updates by EPSS exploit probability.

What to do

Elevated priority: high severity or a meaningful exploitation probability, sooner if an affected product is internet-facing. Senserva flags whether KB5099539 is missing on your devices.

Check if KB5099539 is installed

Copy-paste PowerShell: one machine, or your whole fleet in one pass. No output means the update is not installed.

Get-HotFix covers Windows updates. Office, SharePoint, and Exchange server updates show under installed updates in Programs and Features, or check the Update Catalog history.

Known issues, from Microsoft

Quoted from Microsoft's support article for KB5099539 (checked 2026-07-21). 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 ...

Writing about KB5099539? Cite this page

Copy-paste for a blog post, forum answer, or internal doc. The link always carries the current risk data.

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.

What the press says about this update

Trusted-source coverage of the CVEs this update fixes, pulled live from their own feeds.

Affected products

• Windows 10 Version 1809 for 32-bit Systems
• Windows 10 Version 1809 for x64-based Systems
• Windows Server 2019

Also released in July 2026

The highest-risk updates from the same release:

The full month, summarized: Microsoft Patch Tuesday.

How to install KB5099539

Any of these paths delivers KB5099539; most organizations already have one of the first three running:

• Intune update rings (Windows Update for Business): the update flows on each ring's deferral schedule.
• Windows Autopatch: rings, rollout, and pause or rollback are managed for you; exploited updates can be expedited.
• WSUS / Configuration Manager: approve KB5099539 for your device groups and set a deadline.
• Manual: download from the Update Catalog above and install; fine for a handful of machines, unmanageable at any real scale.

After the rollout, verify rather than assume: update compliance reporting in Intune or Autopatch shows which devices actually installed it, and Siemserva reads Intune, Defender, Autopatch, and Azure Update Manager together to show the devices still missing KB5099539, ranked by exploitation.

Common questions about KB5099539

Does KB5099539 have known issues?

Yes. Microsoft's support article documents known issues for KB5099539 (checked 2026-07-21). The Known issues section on this page quotes it; verify against the article before acting.

Is KB5099539 urgent?

KB5099539 is rated Critical with a maximum CVSS of 9.9. No active exploitation is confirmed yet, so schedule it in your prompt patch cycle.

How do I download KB5099539?

From the Microsoft Update Catalog (linked on this page), or let Intune, Windows Update for Business, Windows Autopatch, or WSUS deliver it. The catalog page lists the download for each supported product.

How do I deploy KB5099539 with Intune?

Assign a Windows Update ring (quality update policy) to the device groups and the update flows on the ring's deferral schedule. For urgent updates, Intune expedite policies can bypass the ring deferrals. Verify the rollout with update compliance reporting rather than assuming delivery.

Can I ask my own AI about KB5099539?

Yes. This page includes a free, ready-to-paste AI prompt containing KB5099539's key facts: severity, CVE count, exploitation status, and the download link. Copy it into Claude, ChatGPT, or Copilot for a rollout plan; the data is refreshed three times a day (5 AM, 12:30 PM, and 7 PM US Central).

Authoritative references