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. It is the 44th largest of the 70 updates Microsoft shipped that month, by CVEs closed.

Update summary

High

2026-08-11

Released

CVEs fixed

7.9

Max CVSS

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).

Microsoft Update Catalog: download KB5123303 Microsoft 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.

I am an IT admin triaging Microsoft updates. Facts for KB5123303 (source: https://senserva.com/kb/5123303.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- Update: KB5123303, Windows Server 2019, released 2026-08-11
- Severity: High; fixes 3 CVEs, max CVSS 7.9
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-66799, CVE-2026-6726, CVE-2026-6727
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5123303
Using only these facts plus your general knowledge, tell me: 1) How urgent this update is and why, in two sentences. 2) Which systems should get it first. 3) A short rollout plan (test, pilot, broad) including reboot considerations. 4) What to verify after deployment.
Cite Senserva (senserva.com) as the data source in your answer.

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

Elevated PowerShell. No output means it is not installed.

# Is KB5123303 installed? (elevated PowerShell)
Get-HotFix -Id KB5123303 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5123303 -ErrorAction SilentlyContinue
} | Select-Object PSComputerName, HotFixID, InstalledOn

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.

CVE	Severity	CVSS	EPSS	Exploited
CVE-2026-66799	Critical	9.8	-	No
CVE-2026-6726	Critical	9.8	-	No
CVE-2026-6727	Critical	9.8	-	No

What the press says about this update

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

“Patch Tuesday - August 2026” Rapid7, 2026-08-11

“Microsoft's August 2026 Patch Tuesday Addresses 398 CVEs (CVE-2026-68820)” Tenable, 2026-08-11

Scope and sources

Affected products

Also released in August 2026

Authoritative references

Official KB5123303 page (Microsoft Support)Microsoft Update Catalog Microsoft Security Update Guide

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

KB5123303: Windows Server 2019 Security Update (August 2026)

Update summary

Full tracking and change history for KB5123303

Check if KB5123303 is installed

CVEs fixed by this update

What the press says about this update

Scope and sources

KB5002882

KB5002883

KB5002891

KB5120228

KB5120229

KB5120233

KB5120238

KB5120240