KB5099538: Windows Server 2019 Security Update (July 2026)

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Download KB5099538

Get the official update for KB5099538. The download and file size for each supported product are on the Microsoft Update Catalog page.

Update summary

Senserva AI Opinion for KB5099538

KB5099538 is the July 2026 Security Update for Windows 10 version 1809 and Windows Server 2019, and it carries two zero-days flagged in the MSRC release document: an AD FS flaw (CVE-2026-56155) exploited in the wild and a BitLocker flaw (CVE-2026-50661) that is publicly disclosed. Organizations still running 1809 or Server 2019 as AD FS federation hosts are the most exposed, since the AD FS issue is under active attack. Note this data is provisional because Microsoft has not yet published per-update CVE detail for this cycle.

Do this: Deploy KB5099538 immediately to any Server 2019 host running AD FS, prioritizing federation servers over general workloads.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for KB5099538

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

Full tracking and change history for KB5099538

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 311 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 9.9 (Critical). EPSS exploit probability up to 7.5%.

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

What to do

Treat as urgent: it is being exploited in the wild (CISA KEV), so patch ahead of items that are not. Senserva flags whether KB5099538 is missing on your devices.

Check if KB5099538 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 KB5099538 (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 2019

This security update includes fixes and quality improvements that are part of the following update:

June 9, 2026—KB5094123 (OS Build 17763.8874)

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] This update changes hotkey unregister and cleanup behavior. In rare cases, some built-in Windows experiences that rely on previous hotkey lifecycle behavior might temporarily stop responding to certain keyboard shortcuts. This issue can typically be resolved by restarting the app affected. If the issue is not resolved, report it through the Feedback Hub.

[Secure Boot]

This update enables dynamic status reporting for Secure Boot states in Windows Security App.

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.

[File Explorer (known issue)] Fixed: An issue where the OneDrive shortcut in File Explorer stops working when File Explorer is run with administrative mode.

[Networking] This update ...

Writing about KB5099538? 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 KB5099538

Any of these paths delivers KB5099538; 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. For this update, consider an expedite policy: it bypasses deferrals for exactly this fix-now case.
• Windows Autopatch: rings, rollout, and pause or rollback are managed for you; exploited updates can be expedited.
• WSUS / Configuration Manager: approve KB5099538 for your device groups and set a deadline (deadline, not just approval, for an exploited fix).
• 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 KB5099538, ranked by exploitation.

Common questions about KB5099538

Does KB5099538 have known issues?

Yes. Microsoft's support article documents known issues for KB5099538 (checked 2026-07-21). The Known issues section on this page quotes it; verify against the article before acting.

Is KB5099538 urgent?

Yes. KB5099538 fixes at least one vulnerability in the CISA Known Exploited Vulnerabilities catalog, meaning attackers are using it in the wild. Deploy it first.

How do I download KB5099538?

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 KB5099538 with Intune?

Assign a Windows Update ring (quality update policy) to the device groups and the update flows on the ring's deferral schedule. Because KB5099538 fixes an actively exploited CVE, an Intune expedite policy is the right tool: it bypasses configured deferrals and pushes the update as soon as devices check in. Verify the rollout with update compliance reporting rather than assuming delivery.

Can I ask my own AI about KB5099538?

Yes. This page includes a free, ready-to-paste AI prompt containing KB5099538'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