Patch tracker / KB5066840

KB5066840: Windows 10 Version 1809 for 32-bit Sys Security Update (October 2025)

KB5066840 is a High security update for Windows 10 Version 1809 for 32-bit Sys, released 2025-10-14. It closes 3 CVEs with a maximum CVSS of 8.8. The most likely of them to be attacked is CVE-2025-59295, which FIRST.org rates at 6% probability of exploitation in the next 30 days.

Update summary

High
2025-10-14
Released
3
CVEs fixed
8.8
Max CVSS
High
Severity
Deploy this cycle
Fixes 3 CVEs for Windows 10 Version 1809 for 32-bit Sys. No confirmed in-the-wild exploitation in this set today.

Fixes 3 CVEs. Most severe CVSS 8.8 (High). EPSS exploit probability up to 1.8%. 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 Windows 11 Version 25H2 for ARM64-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 KB5066840Microsoft support article
Senserva AI Opinion for KB5066840

KB5066840 is the October 14, 2025 rollup covering three CVEs (CVE-2025-59295, CVE-2025-58739, CVE-2025-59208) across a broad install base spanning Windows 11 25H2 on ARM64 and x64 plus the older Windows 10 1809 branch. The top severity is High at CVSS 8.8, but exploitation signals are low: no CISA KEV listing, no ransomware association, and a peak EPSS of only 2 percent. The unusual part here is the mix of a current 25H2 client and a legacy 1809 build in the same KB, so your patch scope may cross very different device generations.

Do this: Deploy KB5066840 through your normal ring schedule and confirm your Windows 10 1809 endpoints are still in support and actually receiving this update.

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

Senserva AI Opinion and rich prompt for KB5066840

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

Full tracking and change history for KB5066840

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 KB5066840 is installed

Elevated PowerShell. No output means it is not installed.

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.

CVESeverityCVSSEPSSExploited
CVE-2025-59295High8.86.0%No
CVE-2025-59208High7.16.0%No
CVE-2025-58739Medium6.56.0%No

Scope and sources

Affected products
Also released in October 2025

KB5070879

1 CVE · Critical · exploited

KB5070881

1 CVE · Critical · exploited

KB5070882

1 CVE · Critical · exploited

KB5070883

1 CVE · Critical · exploited

KB5070884

1 CVE · Critical · exploited

KB5070886

1 CVE · Critical · exploited

KB5070887

1 CVE · Critical · exploited

KB5070892

1 CVE · Critical · exploited

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references
Official KB5066840 page (Microsoft Support)Microsoft Update CatalogMicrosoft Security Update Guide

See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
Provided as is, without warranty; verify against the vendor advisory before acting. Data notice and terms.