Patch tracker / KB5121608

KB5121608: Microsoft Exchange Server Subscription Security Update (September 2026)

KB5121608 is a Critical security update for Microsoft Exchange Server Subscription, released 2026-09-08. It closes 9 CVEs with a maximum CVSS of 9.3. It is the 27th 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 9 CVEs for Microsoft Exchange Server Subscription. No confirmed in-the-wild exploitation in this set today.

Fixes 9 CVEs. Most severe CVSS 9.3 (Critical).

Microsoft Update Catalog: download KB5121608 Microsoft support article

Senserva AI Opinion and rich prompt for KB5121608

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 KB5121608 (source: https://senserva.com/kb/5121608.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed once a day (early morning US Central)):
- Update: KB5121608, Microsoft Exchange Server Subscription, released 2026-09-08
- Severity: Critical; fixes 9 CVEs, max CVSS 9.3
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-55007, CVE-2026-69355, CVE-2026-69356, CVE-2026-69361, CVE-2026-69375, CVE-2026-69378, CVE-2026-69380, CVE-2026-69382 and 1 more
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5121608
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 KB5121608

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 KB5121608 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5121608 installed? (elevated PowerShell)
Get-HotFix -Id KB5121608 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5121608 -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-2026-55007	High	8.1	-	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

What the press says about this update

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

“Microsoft’s September 2026 Patch Tuesday addresses 964 CVEs (CVE-2026-81963, CVE-2026-85880)” Tenable, 2026-09-08

“The September 2026 Security Update Review” Zero Day Initiative, 2026-09-08

Scope and sources

Affected products

Also released in September 2026

Authoritative references

Official KB5121608 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.

KB5121608: Microsoft Exchange Server Subscription Security Update (September 2026)

Update summary

Full tracking and change history for KB5121608

Check if KB5121608 is installed

CVEs fixed by this update

What the press says about this update

Scope and sources

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