Patch tracker / KB5123301

KB5123301: Skype for Business Server 2019 CU8 Security Update (September 2026)

KB5123301 is a Critical security update for Skype for Business Server 2019 CU8, released 2026-09-08. It closes 10 CVEs with a maximum CVSS of 9.8. It is the 24th largest of the 60 updates Microsoft shipped that month, by CVEs closed.

Update summary

Critical

2026-09-08

Released

CVEs fixed

9.8

Max CVSS v3

Critical

Severity

Deploy this cycle

Fixes 10 CVEs for Skype for Business Server 2019 CU8. No confirmed in-the-wild exploitation in this set today.

Fixes 10 CVEs. Most severe CVSS 9.8 (Critical).

Microsoft Update Catalog: download KB5123301 Microsoft support article

Senserva AI Opinion and rich prompt for KB5123301

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 KB5123301 (source: https://senserva.com/kb/5123301.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed once a day (early morning US Central)):
- Update: KB5123301, Skype for Business Server 2019 CU8, released 2026-09-08
- Severity: Critical; fixes 10 CVEs, max CVSS 9.8
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-63523, CVE-2026-66302, CVE-2026-66303, CVE-2026-66304, CVE-2026-66305, CVE-2026-66306, CVE-2026-66307, CVE-2026-66308 and 2 more
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5123301
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 KB5123301

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 KB5123301 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5123301 installed? (elevated PowerShell)
Get-HotFix -Id KB5123301 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5123301 -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-2026-66302	Critical	9.8	-	No
CVE-2026-69646	High	8.3	-	No
CVE-2026-66304	High	7.5	-	No
CVE-2026-66307	High	7.5	-	No
CVE-2026-66305	High	7.1	-	No
CVE-2026-63523	Medium	6.5	-	No
CVE-2026-66303	Medium	6.5	-	No
CVE-2026-66306	Medium	6.5	-	No
CVE-2026-66308	Medium	6.5	-	No
CVE-2026-69642	Medium	6.5	-	No

Scope and sources

Affected products

Also released in September 2026

Authoritative references

Official KB5123301 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.

KB5123301: Skype for Business Server 2019 CU8 Security Update (September 2026)

Update summary

Full tracking and change history for KB5123301

Check if KB5123301 is installed

CVEs fixed by this update

Scope and sources

KB5002916

KB5002923

KB5101346

KB5101347

KB5122871

KB5122876

KB5122878

KB5122880