Patch tracker / KB5066877

KB5066877: Windows Server 2019 Security Update (October 2025)

KB5066877 is a High security update for Windows Server 2019, released 2025-10-14. It closes 34 CVEs with a maximum CVSS of 8.8. At least one of them is actively exploited (CISA KEV), so this is a deploy-first update. The most likely of them to be attacked is CVE-2025-24990, which FIRST.org rates at 6% probability of exploitation in the next 30 days.

Update summary

HighCISA KEV

2025-10-14

Released

CVEs fixed

8.8

Max CVSS

High

Severity

Deploy now

This update fixes vulnerabilities confirmed exploited in the wild.

Fixes 34 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 8.8 (High). EPSS exploit probability up to 6.0%. Among the top 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 Windows 11 Version 25H2 for x64-based Systems has shipped since this one: KB5087423 (2026-06-09). 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 KB5066877 Microsoft support article

Senserva AI Opinion for KB5066877

KB5066877 is the October 14, 2025 cumulative update spanning Windows 11 25H2, Windows 10 1809, and Windows Server 2019, addressing 34 CVEs with a highest Severity of High (CVSS 8.8). One of these CVEs is listed in the CISA Known Exploited Vulnerabilities catalog, meaning active exploitation has been observed even though EPSS peaks at only 6% and none are ransomware-linked. The mix of legacy 1809/Server 2019 and current 25H2 means both aging and freshly deployed fleets need the same patch cycle.

Do this: Prioritize deploying KB5066877 to your Windows Server 2019 and Windows 10 1809 hosts first given the confirmed CISA KEV listing among its fixed CVEs.

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

Senserva AI Opinion and rich prompt for KB5066877

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 KB5066877 (source: https://senserva.com/kb/5066877.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- Update: KB5066877, Windows Server 2019, released 2025-10-14
- Severity: High; fixes 34 CVEs, max CVSS 8.8
- Actively exploited (CISA KEV): YES
- CVEs include: CVE-2016-9535, CVE-2025-24052, CVE-2025-24990, CVE-2025-25004, CVE-2025-55335, CVE-2025-55695, CVE-2025-55700, CVE-2025-55701 and 26 more
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5066877
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 KB5066877

Released: 2025-10-14
Last changed: 2025-10-14
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 KB5066877 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5066877 installed? (elevated PowerShell)
Get-HotFix -Id KB5066877 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5066877 -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-2025-24990	High	7.8	6.0%	KEV
CVE-2025-59230	High	7.8	6.0%	KEV
CVE-2016-9535	Critical	9.9	6.0%	No
CVE-2025-59280	Critical	9.9	6.0%	No
CVE-2025-58718	High	8.8	6.0%	No
CVE-2025-59295	High	8.8	6.0%	No
CVE-2025-24052	High	7.8	6.0%	No
CVE-2025-55701	High	7.8	6.0%	No
CVE-2025-58714	High	7.8	6.0%	No
CVE-2025-59187	High	7.8	6.0%	No
CVE-2025-59201	High	7.8	6.0%	No
CVE-2025-59242	High	7.8	6.0%	No
CVE-2025-59275	High	7.8	6.0%	No
CVE-2025-59277	High	7.8	6.0%	No
CVE-2025-59278	High	7.8	6.0%	No
CVE-2025-58726	High	7.5	6.0%	No
CVE-2025-55335	High	7.4	6.0%	No
CVE-2025-25004	High	7.3	6.0%	No
CVE-2025-59208	High	7.1	6.0%	No
CVE-2025-58725	High	7.0	6.0%	No
CVE-2025-58733	High	7.0	6.0%	No
CVE-2025-58735	High	7.0	6.0%	No
CVE-2025-58736	High	7.0	6.0%	No
CVE-2025-59196	High	7.0	6.0%	No
CVE-2025-59205	High	7.0	6.0%	No
CVE-2025-59282	High	7.0	6.0%	No
CVE-2025-55700	Medium	6.5	6.0%	No
CVE-2025-58717	Medium	6.5	6.0%	No
CVE-2025-58729	Medium	6.5	6.0%	No
CVE-2025-58739	Medium	6.5	6.0%	No
CVE-2025-59214	Medium	6.5	6.0%	No
CVE-2025-55695	Medium	5.5	6.0%	No
CVE-2025-59190	Medium	5.5	6.0%	No
CVE-2025-59198	Medium	5.0	6.0%	No

Scope and sources

Affected products

Also released in October 2025

Authoritative references

Official KB5066877 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.

KB5066877: Windows Server 2019 Security Update (October 2025)

Update summary

Full tracking and change history for KB5066877

Check if KB5066877 is installed

CVEs fixed by this update

Scope and sources

KB5070879

KB5070881

KB5070882

KB5070883

KB5070884

KB5070886

KB5070887

KB5070892