Patch tracker / KB5123303

KB5123303: Windows Server 2019 Security Update (August 2026)

KB5123303 is a High security update for Windows Server 2019, released 2026-08-11. It closes 3 CVEs with a maximum CVSS of 7.9. The most likely of them to be attacked is CVE-2026-66799, which FIRST.org rates at 6% probability of exploitation in the next 30 days.

Update summary

High
2026-08-11
Released
3
CVEs fixed
7.9
Max CVSS v3
High
Severity
Deploy this cycle
Fixes 3 CVEs for Windows Server 2019. No confirmed in-the-wild exploitation in this set today.

Fixes 3 CVEs. Most severe CVSS 7.9 (High). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.

Senserva found thiswe track every release for this product line, so we can tell you this package is behind

A newer security update for Windows 10 Version 1809 for 32-bit Systems has shipped since this one: KB5122871 (2026-09-08). 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.

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Microsoft documents 1 known issue with this update.

  • Microsoft is not currently aware of any issues with this update.

The full text, quoted from Microsoft

Microsoft Update Catalog: download KB5123303Microsoft support article
Senserva AI Opinion and rich prompt for KB5123303

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

Full tracking and change history for KB5123303

Released
2026-08-11
Last changed
2026-08-11
Changes tracked
1

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.

Check if KB5123303 is installed

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Known issues, from Microsoft

Quoted from Microsoft's support article for KB5123303 (checked 2026-09-12). Verify against the article before acting.

Microsoft is not currently aware of any issues with this update.

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.

CVESeverityCVSSEPSSExploited
CVE-2026-6727Critical9.86.2%No
CVE-2026-6726High7.96.2%No
CVE-2026-66799High7.86.2%No

Scope and sources

Affected products
Also released in August 2026

KB5002882

39 CVEs · Critical · exploited

KB5002883

40 CVEs · Critical · exploited

KB5002891

40 CVEs · Critical · exploited

KB5120228

215 CVEs · Critical · exploited

KB5120229

195 CVEs · Critical · exploited

KB5120233

215 CVEs · Critical · exploited

KB5120238

183 CVEs · Critical · exploited

KB5120240

170 CVEs · Critical · exploited

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references
Official KB5123303 page (Microsoft Support)Microsoft Update CatalogMicrosoft Security Update Guide

See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
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