Patch tracker / KB5121611

KB5121611: Microsoft Exchange Server 2019 Cumulat Security Update (September 2026)

KB5121611 is a Critical security update for Microsoft Exchange Server 2019 Cumulat, released 2026-09-08. It closes 8 CVEs with a maximum CVSS of 9.3. It is the 30th largest of the 60 updates Microsoft shipped that month, by CVEs closed.

Update summary

Critical

2026-09-08

Released

CVEs fixed

9.3

Max CVSS v3

Critical

Severity

Deploy this cycle

Fixes 8 CVEs for Microsoft Exchange Server 2019 Cumulat. No confirmed in-the-wild exploitation in this set today.

Fixes 8 CVEs. Most severe CVSS 9.3 (Critical).

Microsoft Update Catalog: download KB5121611 Microsoft support article

Senserva AI Opinion and rich prompt for KB5121611

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 KB5121611 (source: https://senserva.com/kb/5121611.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed once a day (early morning US Central)):
- Update: KB5121611, Microsoft Exchange Server 2019 Cumulat, released 2026-09-08
- Severity: Critical; fixes 8 CVEs, max CVSS 9.3
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-69355, CVE-2026-69356, CVE-2026-69361, CVE-2026-69375, CVE-2026-69378, CVE-2026-69380, CVE-2026-69382, CVE-2026-69641
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5121611
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 KB5121611

Released: 2026-09-08
Last changed: 2026-09-08
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 KB5121611 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5121611 installed? (elevated PowerShell)
Get-HotFix -Id KB5121611 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5121611 -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-2026-69356	Critical	9.3	-	No
CVE-2026-69641	Critical	9.1	-	No
CVE-2026-69355	High	8.8	-	No
CVE-2026-69380	High	8.1	-	No
CVE-2026-69378	High	7.5	-	No
CVE-2026-69361	Medium	6.5	-	No
CVE-2026-69375	Medium	6.5	-	No
CVE-2026-69382	Medium	5.9	-	No

Scope and sources

Affected products

Also released in September 2026

Authoritative references

Official KB5121611 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.

KB5121611: Microsoft Exchange Server 2019 Cumulat Security Update (September 2026)

Update summary

Full tracking and change history for KB5121611

Check if KB5121611 is installed

CVEs fixed by this update

Scope and sources

KB5122871

KB5122876

KB5122878

KB5122880

KB5122882

KB5123065

KB5123066

KB5123099