Patch tracker / KB5066835

KB5066835: Windows Server 2019 Security Update (December 2025)

KB5066835 is a Critical security update for Windows Server 2019, released 2025-12-09. It closes 134 CVEs with a maximum CVSS of 9.9. 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-2025-2884, which FIRST.org rates at 26% probability of exploitation in the next 30 days.

Update summary

CriticalCISA KEV
2025-12-09
Released
134
CVEs fixed
9.9
Max CVSS
Critical
Severity
Deploy now
This update fixes vulnerabilities confirmed exploited in the wild.

Fixes 134 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 9.9 (Critical). 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.

Senserva found thisread these before you deploy broadly

Microsoft documents 4 known issues with this update.

  • Problems playing protected content in some BluRay/DVD/Digital TV apps
  • USB mouse and keyboard not working in the Windows Recovery Environment
  • IIS websites might fail to load

The full text, quoted from Microsoft

Microsoft Update Catalog: download KB5066835Microsoft support article
Senserva AI Opinion for KB5066835

KB5066835 is a December 2025 rollup for Windows 10 1809 and Windows Server 2019 that patches 134 CVEs, with a top Critical rating at CVSS 9.9. One of the included CVEs is already listed in the CISA Known Exploited Vulnerabilities catalog, though none are tied to ransomware campaigns yet. The confirmed exploitation plus the sheer patch volume makes this a priority for any remaining 1809 or Server 2019 fleet.

Do this: Deploy KB5066835 to all Windows 10 1809 and Server 2019 systems now, prioritizing internet-facing Server 2019 hosts given the confirmed KEV-listed CVE.

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

Senserva AI Opinion and rich prompt for KB5066835

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

Full tracking and change history for KB5066835

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 KB5066835 is installed

Elevated PowerShell. No output means it is not installed.

Known issues, from Microsoft

Quoted from Microsoft's support article for KB5066835 (checked 2026-08-04). Verify against the article before acting.

Problems playing protected content in some BluRay/DVD/Digital TV apps

Symptoms

Some Digital TV and Blu-ray/DVD apps might not play protected content as expected after installing the August 29, 2025, Windows non-security preview update ( KB5064081 ), or later updates.

Apps that use Enhanced Video Renderer with HDCP enforcement or Digital Rights Management (DRM) for digital audio might show copyright protection errors, frequent playback interruptions, unexpected stops, or black screens.

Streaming services are not affected.

Workaround

The non-security September 2025 Windows preview update ( KB5065789 ) and later updates address problems affecting certain applications that use the Enhanced Video Renderer (EVR) with HDCP (High-bandwidth Digital Content Protection) enforcement . The non-security October Windows preview update ( KB5067036 ) includes additional improvements to address problems affecting applications using Digital Rights Media (DRM) for digital audio .

USB mouse and keyboard not working in the Windows Recovery Environment

Symptoms

After installing October 2025 security update ( KB5066835 ), USB devices, such as keyboards and mice, do not function in the Windows Recovery Environment (WinRE) . This issue prevents navigation of any of the recovery options within WinRE. Note that the USB keyboard and mouse continue to work normally within the Windows operating system. ...

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-2025-49708Critical9.96.0%No
CVE-2025-59280Critical9.96.0%No
CVE-2025-59284Critical9.96.0%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-2025-50175High7.86.0%No
CVE-2025-53150High7.86.0%No
CVE-2025-53768High7.86.0%No
CVE-2025-55328High7.86.0%No
CVE-2025-55339High7.86.0%No
CVE-2025-55677High7.86.0%No
CVE-2025-55680High7.86.0%No
CVE-2025-55692High7.86.0%No
CVE-2025-55694High7.86.0%No
CVE-2025-55696High7.86.0%No
CVE-2025-55697High7.86.0%No
CVE-2025-55701High7.86.0%No
CVE-2025-58714High7.86.0%No
CVE-2025-58720High7.86.0%No
CVE-2025-58722High7.86.0%No
CVE-2025-58728High7.86.0%No
CVE-2025-59187High7.86.0%No
CVE-2025-59191High7.86.0%No
CVE-2025-59192High7.86.0%No
CVE-2025-59199High7.86.0%No
CVE-2025-59201High7.86.0%No
CVE-2025-59207High7.86.0%No
CVE-2025-59241High7.86.0%No
CVE-2025-59242High7.86.0%No
CVE-2025-59254High7.86.0%No
CVE-2025-59255High7.86.0%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-2025-53139High7.76.0%No
CVE-2025-55698High7.76.0%No
CVE-2025-59200High7.76.0%No
CVE-2025-55326High7.56.0%No
CVE-2025-58726High7.56.0%No
CVE-2025-48004High7.46.0%No
CVE-2025-55335High7.46.0%No
CVE-2025-55687High7.46.0%No
CVE-2025-55693High7.46.0%No
CVE-2025-59189High7.46.0%No
CVE-2025-59206High7.46.0%No
CVE-2025-59210High7.46.0%No
CVE-2025-25004High7.36.0%No
CVE-2025-59208High7.16.0%No
CVE-2025-50174High7.06.0%No
CVE-2025-53717High7.06.0%No
CVE-2025-54957High7.06.0%No
CVE-2025-55331High7.06.0%No
CVE-2025-55340High7.06.0%No
CVE-2025-55678High7.06.0%No
CVE-2025-55681High7.06.0%No
CVE-2025-55684High7.06.0%No
CVE-2025-55685High7.06.0%No
CVE-2025-55686High7.06.0%No
CVE-2025-55688High7.06.0%No
CVE-2025-55689High7.06.0%No
CVE-2025-55690High7.06.0%No
CVE-2025-55691High7.06.0%No
CVE-2025-58725High7.06.0%No
CVE-2025-58727High7.06.0%No
CVE-2025-58730High7.06.0%No
CVE-2025-58731High7.06.0%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-2025-58738High7.06.0%No
CVE-2025-59193High7.06.0%No
CVE-2025-59194High7.06.0%No
CVE-2025-59195High7.06.0%No
CVE-2025-59196High7.06.0%No
CVE-2025-59202High7.06.0%No
CVE-2025-59205High7.06.0%No
CVE-2025-59261High7.06.0%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-2025-59257Medium6.56.0%No
CVE-2025-59259Medium6.56.0%No
CVE-2025-48813Medium6.36.0%No
CVE-2025-55334Medium6.26.0%No
CVE-2025-59258Medium6.26.0%No
CVE-2025-55330Medium6.16.0%No
CVE-2025-55332Medium6.16.0%No
CVE-2025-55333Medium6.16.0%No
CVE-2025-55337Medium6.16.0%No
CVE-2025-55338Medium6.16.0%No
CVE-2025-55682Medium6.16.0%No
CVE-2025-47979Medium5.56.0%No
CVE-2025-55325Medium5.56.0%No
CVE-2025-55336Medium5.56.0%No
CVE-2025-55676Medium5.56.0%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-2025-59204Medium5.56.0%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-2025-2884Medium5.326%No
CVE-2025-55679Medium5.16.0%No
CVE-2025-59198Medium5.06.0%No
CVE-2025-58719Medium4.76.0%No

Scope and sources

Affected products
Also released in December 2025

KB5066586

98 CVEs · Critical · exploited

KB5066780

114 CVEs · Critical · exploited

KB5066782

103 CVEs · Critical · exploited

KB5066791

98 CVEs · Critical · exploited

KB5066793

108 CVEs · Critical · exploited

KB5068779

32 CVEs · Critical · exploited

KB5068781

33 CVEs · Critical · exploited

KB5068787

30 CVEs · Critical · exploited

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references
Official KB5066835 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.