Microsoft closed out 2025 with a December Patch Tuesday that feels very on-brand: 57 vulnerabilities fixed across Windows and core Microsoft platforms, three zero days in the spotlight, and one already actively exploited. It is not the no-drama year-end wrap many admins were hoping for, but it is also not a chaotic fire drill if you know where to look first.
What Microsoft Shipped
The December security bundle covers 57 flaws that Microsoft formally counts for Patch Tuesday, ranging from privilege-elevation vulnerabilities deep in Windows internals to remote code-execution issues in Office and PowerShell. On top of that, another set of security fixes landed recently in the Chromium-based Edge browser, which Microsoft tracks separately from the main Patch Tuesday tally.
The Actively Exploited Zero Day
The headline vulnerability is CVE-2025-62221, a privilege elevation vulnerability in the Windows Cloud Files Mini Filter Driver that Microsoft says is being actively exploited. The flaw is rated Important, not Critical. Successful exploitation allows an authenticated attacker to escalate to the SYSTEM level on a compromised machine.
Microsoft’s advisory confirms that both its Threat Intelligence Center and Security Response Center were involved in discovering and reporting the issue, and that CISA has already added it to the Known Exploited Vulnerabilities catalog, with a remediation deadline for federal agencies.
Two More Zero Days In The Mix
The other two zero-day patches this month live slightly higher in the stack and target how code is executed rather than how the kernel deals with storage internals. Neither vulnerability has been confirmed as exploited yet.
CVE-2025-54100 affects Windows PowerShell and is an RCE vulnerability arising from command injection when web content is parsed via commands like Invoke-WebRequest. In plain terms, it is a parsing problem that crafted content can sneak commands into what should be treated as data, potentially letting an attacker run arbitrary code under the security context of the user executing the script.
CVE-2025-64671 affects GitHub Copilot for JetBrains IDEs. It stems from a command injection weakness. Copilot doesn’t properly neutralise special elements in a command before passing them along, which opens the door for an attacker to inject and run arbitrary code on the host system
Microsoft’s fix for the PowerShell issue adds safeguards to prevent unintended script execution when using Invoke-WebRequest, effectively pushing users toward safer parsing patterns. It’s a reminder for administrators to review any script that reaches out to the internet. In JetBrains environments, the focus for Copilot is on tightening the flow of commands from AI suggestions to local execution, so developer machines do not become an easy bridge from code to compromise.
Outside the zero days, three critical remote code execution vulnerabilities stand out in the December lineup: two in Microsoft Office and one in Outlook. These bugs are classic high-impact territory because successful exploitation can allow code execution simply by getting a user to open or render crafted Office content.
The Microsoft Security Update Guide lists two critical Office RCEs and a critical Outlook RCE, each mapped to common user workflows such as opening documents or processing email content, across fully supported versions of Office and Microsoft 365 apps. For defenders, the nuance is that these are exactly the entry points frequently abused in phishing and malware campaigns, so they should sit very close to the zero days in any patching plan.
Independent analysis from security vendors and researchers largely reinforces Microsoft’s prioritization, with most advisories recommending that organizations treat the Windows zero-day, the PowerShell RCE, and the Office critical bugs as first-tier patch targets. December’s Patch Tuesday is not the loudest release of the year, but it is quietly important because it touches three familiar pressure points at once: Windows kernel-level privilege escalation, PowerShell as an automation workhorse, and Office as the front door to many attacks.
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