Microsoft’s final update cycle of 2025 delivered a wide range of security patches, quality improvements, and feature refinements across Windows, Office, Exchange, Azure components, and Microsoft 365 services. With 56–57 security vulnerabilities fixed depending on reporting source, including multiple zero‑day vulnerabilities, this was one of the most important security releases of the year.
Below is a breakdown of what was included, what issues were discovered post‑deployment, and why these updates are critical for organisations and end‑users.
What Was Included in the December 2025 Microsoft Updates
Security Fixes Across Windows, Office, Exchange & Azure
Microsoft addressed 56–57 security vulnerabilities, including:
- 28 Elevation of Privilege vulnerabilities
- 19 Remote Code Execution vulnerabilities
- 4 Information Disclosure vulnerabilities
- 3 Denial of Service vulnerabilities
- 2 Spoofing vulnerabilities
Several high‑risk components were patched, including:
- Windows Cloud Files Mini Filter Driver (CVE‑2025‑62221) — actively exploited zero‑day allowing SYSTEM‑level privilege escalation.
- GitHub Copilot for JetBrains (CVE‑2025‑64671) — remote code execution via improper command sanitisation.
- PowerShell RCE (CVE‑2025‑54100) — command injection leading to local code execution.
These updates affected key product families including Windows 10/11, Office (Word, Excel, Outlook), SharePoint, Hyper‑V, Azure Monitor Agent, Windows Firewall, and various system drivers.
2. Windows 11 Quality & Feature Enhancements
The December 2025 cumulative updates for Windows 11 (KB5072033) delivered numerous improvements such as:
- Complete dark mode overhaul for File Explorer
- Start menu, taskbar and search UI refinements
- Better performance in gaming & multitasking
- Updates to Copilot+ PC AI components
These enhancements were rolled into Windows 11 24H2 (Build 26100.7462) and 25H2 (Build 26200.7462).
3. Office Updates (December 2025)
Microsoft pushed multiple Office security updates covering:
- Excel 2016
- Word 2016
- Office 2016 suite
- SharePoint Server (2016, 2019, Subscription Edition)
- Office Online Server
These patches addressed remote code execution vulnerabilities through malicious documents or preview pane attacks.
4. Microsoft 365 and Intune Updates
Released December 4, 2025, these included:
- Expansion of Microsoft 365 Copilot Chat across Office apps
- New Zero Trust and email security protections (Defender for Office)
- Improved endpoint management with Intune Plan 2 capabilities
- Automation through Security Copilot agents
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Known Issues After Installing the December 2025 Updates
1. Windows Boot Failures (Highly Impactful)
Devices that previously failed to install the December 2025 update were left in an “improper state.” Installing later updates (particularly January 2026 KB5074109) caused:
- UNMOUNTABLE_BOOT_VOLUME (0xED) BSOD
- Systems becoming unable to boot without manual recovery
Microsoft confirmed this issue particularly affected commercial/enterprise devices, not consumers.
2. MSMQ (Message Queuing) Failures After Update
The December rollups introduced security changes to NTFS permissions on the MSMQ storage directory, causing:
- MSMQ queues becoming inactive
- IIS and legacy apps failing with “Insufficient resources to perform operation”
- Misleading disk/memory error logs
Root cause: security model change requiring explicit write permission for identities that previously inherited it automatically.
3. Outlook, File Explorer & System Instability (Post‑Update Side‑Effects)
Reported issues included:
- Outlook freezing or failing when PST files stored in OneDrive
- Remote Desktop login failures
- File Explorer customisation issues
- S3 sleep mode failures on older devices
- Shutdown/reboot failures
Microsoft issued emergency patch KB5078127 to address crashing apps and OneDrive‑related issues.
Despite the issues seen on some systems, installing these updates remains critically important.
Why It’s Necessary to Install the December 2025 Updates
Despite the issues seen on some systems, installing these updates remains critically important.
1. Active Zero‑Day Exploits Were Fixed
At least one vulnerability (CVE‑2025‑62221) was being actively exploited in the wild.
- Attackers could gain full SYSTEM privileges
- Could lead to ransomware, persistence, and lateral movement
[cybersecur…tynews.com]
2. High‑Risk RCE and Privilege Escalation Vulnerabilities
Several Office and system‑level RCE vulnerabilities required immediate patching to prevent:
- Drive‑by document exploits
- Email preview‑pane attacks
- Local privilege escalation in Windows core components
[krebsonsecurity.com]
3. Updates Improve Stability, Security Baselines & Compatibility
Windows updates enhance:
- Cloud file system reliability
- Windows Defender Firewall hardening
- Hyper‑V security
- Overall OS servicing stack health
[petri.com]
4. Microsoft 365 Security Maturity Advances
Organisations benefit from:
- Strengthened Zero Trust posture
- Enhanced phishing and malware protections
- AI‑driven detection via Security Copilot
[blog.sonnes.cloud]
5. Extended Support and Compliance
Security updates are required to maintain:
- ISO27001 compliance
- Cyber Essentials / Cyber Essentials Plus controls
- Vendor security requirements for Windows and Office environments
(This is implied across Microsoft’s security guidance and patch bulletins.)
The December 2025 Microsoft updates form one of the most important security releases of the year, closing actively exploited vulnerabilities and strengthening critical components across Windows, Office, Azure, and Microsoft 365.
While some issues emerged—such as boot failures and MSMQ disruptions—Microsoft has acknowledged, documented, and released further guidance and fixes. For enterprises, the cost of not patching—especially with known exploited vulnerabilities—far outweighs the operational friction caused by the update cycle.
