Patch tracker / KB5071875

KB5071875: Microsoft Exchange Server Subscription Security Update (December 2025)

KB5071875 is a High security update for Microsoft Exchange Server Subscription, released 2025-12-09. It closes 2 CVEs with a maximum CVSS of 7.5. It is the 47th largest of the 59 updates Microsoft shipped that month, by CVEs closed.

Update summary

High

2025-12-09

Released

CVEs fixed

7.5

Max CVSS v3

High

Severity

Deploy this cycle

Fixes 2 CVEs for Microsoft Exchange Server Subscription. No confirmed in-the-wild exploitation in this set today.

Fixes 2 CVEs. Most severe CVSS 7.5 (High). EPSS exploit probability up to 1.0%. 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 Microsoft Exchange Server Subscription Edition RTM has shipped since this one: KB5121573 (2026-08-11). 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.

Microsoft Update Catalog: download KB5071875 Microsoft support article

Senserva AI Opinion for KB5071875

KB5071875 is the December 2025 patch covering all three current Exchange on-premises builds: Subscription Edition RTM, 2016 CU23, and 2019 CU15, fixing CVE-2025-64667 and CVE-2025-64666. Highest Severity is High at CVSS 7.5 with EPSS at 1 percent, and neither CVE is in CISA KEV or linked to ransomware. Because it spans every supported Exchange version including the new Subscription Edition, any organization still running mail on-premises is in scope regardless of which build they are on.

Do this: Identify your Exchange build (SE RTM, 2016 CU23, or 2019 CU15) and schedule KB5071875 in your next maintenance window.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for KB5071875

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 KB5071875 (source: https://senserva.com/kb/5071875.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- Update: KB5071875, Microsoft Exchange Server Subscription, released 2025-12-09
- Severity: High; fixes 2 CVEs, max CVSS 7.5
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2025-64666, CVE-2025-64667
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5071875
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 KB5071875

Released: 2025-12-09
Last changed: 2026-07-08
Changes tracked: 2

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 KB5071875 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5071875 installed? (elevated PowerShell)
Get-HotFix -Id KB5071875 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5071875 -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-2025-64666	High	7.5	1.0%	No
CVE-2025-64667	Medium	5.3	1.0%	No

Scope and sources

Affected products

Also released in December 2025

Authoritative references

Official KB5071875 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.

KB5071875: Microsoft Exchange Server Subscription Security Update (December 2025)

Update summary

Full tracking and change history for KB5071875

Check if KB5071875 is installed

CVEs fixed by this update

Scope and sources

KB5066586

KB5066780

KB5066782

KB5066791

KB5066793

KB5066835

KB5068779

KB5068781