Microsoft closed out 2025 with a modest-but-important Patch Tuesday: fixes for 56 security flaws across Windows, Office, Edge and related components — among them one vulnerability being actively exploited and two separate zero‑day command‑injection bugs.
What landed and why you should care
The December release covers a broad swath of issues: three rated Critical and 53 rated Important, spanning privilege escalation, remote code execution, information disclosure and denial‑of‑service bugs. On the surface the count — 56 CVEs — looks smaller than some recent months, but the mix contains high‑impact items that can be chained or weaponized by attackers.
The most urgent item is CVE‑2025‑62221, a use‑after‑free in the Windows Cloud Files Mini Filter Driver (CVSS 7.8). Microsoft says this bug has been found in the wild; CISA added it to its Known Exploited Vulnerabilities catalog and set a December 30 deadline for federal agencies to apply the patch. Because the Cloud Files minifilter is a common interception layer for services like OneDrive and other cloud sync tools, successful exploitation can enable local privilege escalation to SYSTEM — a handy next step for adversaries who already have a low‑privileged foothold.
Two other high‑profile vulnerabilities are listed as zero‑days (publicly known) at release time:
- CVE‑2025‑54100 — a command injection in Windows PowerShell that affects how web content is processed by commands such as Invoke‑WebRequest. Microsoft’s patch changes PowerShell behavior and will surface a security warning when the command is used in ways that previously allowed crafted content to trigger execution.
- CVE‑2025‑64671 — a command injection in GitHub Copilot for JetBrains; it lets an attacker craft inputs (for example via malicious files or MCP servers) that trick agentic IDE features into running commands that bypass a user’s allow list or auto‑approve settings.
- Office and Outlook continue to be a recurring theme: a set of Office RCEs tied to preview/preview‑pane and message handling were patched this month. ZDI and other analysts flagged multiple Office/Excel/Word entries with RCE potential.
- Several kernel and file‑system related EoP (elevation of privilege) fixes landed across Cloud Files, Projected File System, ReFS and other components — these are the sort of local bugs attackers love to stitch together with phishing or an initial remote compromise.
- Microsoft also bundled third‑party Chromium fixes for Edge (including a spoofing bug on Edge for macOS/iOS) and a number of Chromium CVEs are included in the overall list.
The Copilot bug follows the broader pattern security researchers have dubbed “IDEsaster,” where agentic IDE plugins and model‑backed features introduce new attack surfaces such as cross‑prompt injections and malicious Model Context Protocol (MCP) servers.
A few notable specifics
If you’re counting totals for 2025 you’ll see differing numbers: some trackers put Microsoft’s annual CVE count above 1,200, while others report a lower figure. The variance comes from whether third‑party (Chromium) CVEs and Azure‑specific Linux fixes are included. The practical point: it’s been a big year for patches and 2026 looks set to continue that trend.
Practical steps for defenders (and admins)
1. Prioritize CVE‑2025‑62221 immediately — patch systems that use Windows Cloud Files components and reboot where required. If you can’t patch right away, isolate affected hosts and harden remote access paths.
2. Apply the PowerShell update and plan for the Invoke‑WebRequest behavior change: patched systems will present warnings that can break some scripts. Test automation in a staging environment before wide deployment.
3. Update JetBrains IDEs and the GitHub Copilot plugin (or remove/disable agentic features) until you’ve confirmed your environment’s MCP and file trust settings are safe. Treat agentic IDE capabilities as a new risk domain — the community expects more similar issues in 2026.
4. Don’t ignore Office/Outlook updates — preview‑pane and message parsing RCEs keep appearing. Mac Office LTSC updates lag in some cases; check platform coverage carefully.
5. Review detection and EDR telemetry for signs of privilege‑escalation chains: look for signed driver loads, kernel module installs, abnormal use of system tools and credential theft activity following a low‑privileged foothold.
A short note on mitigations and usability
Microsoft’s PowerShell patch doesn’t just close a parsing bug; it intentionally changes the user experience by warning on certain Invoke‑WebRequest usage patterns. That means admins should expect some operational friction — but it’s a good trade for blocking a simple command‑injection path that attackers could exploit after coaxing a user to run a script.
For organizations using agentic coding assistants or Copilot variants inside IDEs, the December fixes are a reminder that convenience features can expand the attack surface. If your workflows rely on auto‑approved terminal commands, audit those settings now.
Where this fits in the broader security landscape
Patch cycles keep getting denser as software grows and AI‑driven tooling becomes more tightly integrated with developer environments. Microsoft’s Copilot/IDE agent issues here echo wider concerns about prompt‑injection and model‑context attacks — the same class of problems that researchers highlighted in the recent IDEsaster findings. If you follow Microsoft’s AI roadmap, this is one of the practical security consequences of embedding models deeper into dev and ops workflows; consider auditing those integrations alongside your standard patch program. See Microsoft’s broader AI work for context in how these features are evolving: Microsoft Unveils MAI‑Image‑1, Its First In‑House Text‑to‑Image Model.
If you’re running or managing Windows desktops and servers, this month’s update is also a good spur to tidy up lingering cruft and automation that relies on lax PowerShell behavior — you may find it useful to consult practical cleanup steps for modern Windows installs if you’re about to mass‑deploy updates: How to Declutter Windows 11 25H2.
Final note for operators
This patch cycle doesn’t have the highest numeric total of the year, but the presence of an actively exploited use‑after‑free and two zero‑days tied to PowerShell and agentic IDEs gives it outsized operational impact. Apply updates, test your critical automation, and treat agentic developer tools as a security priority rather than a productivity-only feature.
Stay alert: attackers will continue to combine social engineering, remote bugs and local elevation flaws to move from foothold to full control — and defenders who patch methodically and test changes in staging will be harder to outmaneuver.