Patch tracker / KB5066836

KB5066836: Windows Server 2019 Security Update (December 2025)

KB5066836 is a High security update for Windows Server 2019, released 2025-12-09. It closes 78 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-2025-55248, which FIRST.org rates at 66% probability of exploitation in the next 30 days.

Update summary

HighCISA KEV
2025-12-09
Released
78
CVEs fixed
8.8
Max CVSS
High
Severity
Deploy now
This update fixes vulnerabilities confirmed exploited in the wild.

Fixes 78 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 10 Version 1809 for 32-bit Systems has shipped since this one: KB5094041 (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 KB5066836Microsoft support article
Senserva AI Opinion for KB5066836

KB5066836 is the December 9, 2025 rollup for Windows 10 1809 and Windows Server 2019, fixing 78 CVEs with a highest Severity of High (CVSS 8.8). One of these CVEs is listed in the CISA Known Exploited Vulnerabilities catalog, though none are tied to ransomware and the highest EPSS is only 6%. Server 2019 shops running domain controllers or legacy 1809 endpoints are the primary exposure here.

Do this: Prioritize deploying KB5066836 to any remaining 1809 and Server 2019 systems first, given the confirmed CISA KEV-listed CVE among the 78 fixes.

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

Senserva AI Opinion and rich prompt for KB5066836

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

Full tracking and change history for KB5066836

Released
2025-12-09
Last changed
2026-07-12
Changes tracked
3

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 KB5066836 is installed

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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-2025-24990High7.86.0%KEV
CVE-2025-59230High7.86.0%KEV
CVE-2025-47827Medium4.66.0%KEV
CVE-2016-9535Critical9.96.0%No
CVE-2025-59280Critical9.96.0%No
CVE-2025-59294Critical9.96.0%No
CVE-2025-58715High8.86.0%No
CVE-2025-58716High8.86.0%No
CVE-2025-58718High8.86.0%No
CVE-2025-59295High8.86.0%No
CVE-2025-24052High7.86.0%No
CVE-2025-50152High7.86.0%No
CVE-2025-53768High7.86.0%No
CVE-2025-55328High7.86.0%No
CVE-2025-55692High7.86.0%No
CVE-2025-55701High7.86.0%No
CVE-2025-58714High7.86.0%No
CVE-2025-58722High7.86.0%No
CVE-2025-59187High7.86.0%No
CVE-2025-59192High7.86.0%No
CVE-2025-59201High7.86.0%No
CVE-2025-59242High7.86.0%No
CVE-2025-59254High7.86.0%No
CVE-2025-59275High7.86.0%No
CVE-2025-59277High7.86.0%No
CVE-2025-59278High7.86.0%No
CVE-2025-64679High7.86.0%No
CVE-2025-64680High7.86.0%No
CVE-2025-59200High7.76.0%No
CVE-2025-58726High7.56.0%No
CVE-2025-55335High7.46.0%No
CVE-2025-55687High7.46.0%No
CVE-2025-25004High7.36.0%No
CVE-2025-59208High7.16.0%No
CVE-2025-54957High7.06.0%No
CVE-2025-55678High7.06.0%No
CVE-2025-58725High7.06.0%No
CVE-2025-58730High7.06.0%No
CVE-2025-58732High7.06.0%No
CVE-2025-58733High7.06.0%No
CVE-2025-58734High7.06.0%No
CVE-2025-58735High7.06.0%No
CVE-2025-58736High7.06.0%No
CVE-2025-58737High7.06.0%No
CVE-2025-59196High7.06.0%No
CVE-2025-59202High7.06.0%No
CVE-2025-59205High7.06.0%No
CVE-2025-59282High7.06.0%No
CVE-2025-55700Medium6.56.0%No
CVE-2025-58717Medium6.56.0%No
CVE-2025-58729Medium6.56.0%No
CVE-2025-58739Medium6.56.0%No
CVE-2025-59185Medium6.56.0%No
CVE-2025-59214Medium6.56.0%No
CVE-2025-59244Medium6.56.0%No
CVE-2025-59259Medium6.56.0%No
CVE-2025-59258Medium6.26.0%No
CVE-2025-55333Medium6.16.0%No
CVE-2025-55338Medium6.16.0%No
CVE-2025-55325Medium5.56.0%No
CVE-2025-55683Medium5.56.0%No
CVE-2025-55695Medium5.56.0%No
CVE-2025-55699Medium5.56.0%No
CVE-2025-59184Medium5.56.0%No
CVE-2025-59186Medium5.56.0%No
CVE-2025-59188Medium5.56.0%No
CVE-2025-59190Medium5.56.0%No
CVE-2025-59197Medium5.56.0%No
CVE-2025-59203Medium5.56.0%No
CVE-2025-59209Medium5.56.0%No
CVE-2025-59211Medium5.56.0%No
CVE-2025-59253Medium5.56.0%No
CVE-2025-59260Medium5.56.0%No
CVE-2025-62208Medium5.56.0%No
CVE-2025-62209Medium5.56.0%No
CVE-2025-59198Medium5.06.0%No
CVE-2025-55248Medium4.866%No
CVE-2025-58719Medium4.76.0%No

Scope and sources

Affected products
Also released in December 2025

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134 CVEs · Critical · exploited

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32 CVEs · Critical · exploited

KB5068781

33 CVEs · Critical · exploited

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references
Official KB5066836 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.