December 2025 Patch Tuesday: The Real Playbook

December 2025 Patch Tuesday isn’t a routine maintenance window. It’s a triage sprint with one actively exploited Windows privilege escalation (CVE‑2025‑62221), two more zero‑days, and a high‑risk command‑injection bug in the GitHub Copilot plug‑in for JetBrains IDEs. The good news: all are patchable right now. The bad news: you have developer endpoints and build agents where “we’ll get to it later” turns into real compromise. Let’s fix that—quickly, and with proof.

Here’s the thing: attackers love December because people defer restarts and delay change windows. Don’t. Treat this release like an incident response task and move in 48 hours. Below, you’ll get the exact updates to apply, how to verify them, and a short checklist to close the gaps that patching alone doesn’t catch.

December 2025 Patch Tuesday: what actually changed

On December 10, 2025, Microsoft shipped fixes for 57 vulnerabilities across Windows and related components, including three zero‑days—one of which (CVE‑2025‑62221) was already exploited in the wild. Most issues cluster around elevation‑of‑privilege (EoP) and remote code execution (RCE), which remain the fastest paths to domain‑wide impact. (tomsguide.com)

The standout is CVE‑2025‑62221, a use‑after‑free in the Windows Cloud Files Mini Filter Driver (cldflt.sys). It turns local, low‑privileged access into SYSTEM—exactly what post‑phish and initial foothold playbooks need. CISA has listed the CVE in its Known Exploited Vulnerabilities (KEV) catalog, which typically elevates urgency for federal and enterprise teams alike. (rapid7.com)

Also notable: a command‑injection vulnerability in the GitHub Copilot plug‑in for JetBrains (CVE‑2025‑64671) and a PowerShell RCE involving Invoke‑WebRequest (CVE‑2025‑54100). If your developers live in IntelliJ‑based IDEs, or if your automation relies on scripted downloads, these aren’t theoretical risks. (cybersecurity-help.cz)

Why CVE‑2025‑62221 matters more than its 7.8 score

Scores are signals, not destiny. CVE‑2025‑62221 sits in the kernel‑mode Cloud Files Mini Filter used by OneDrive and other sync clients; it executes with high privileges and is already being abused. In practice, that means any adversary who landed a low‑privilege foothold (phished creds, vulnerable Electron app, unpatched browser plug‑in) can escalate to SYSTEM and persist. (expel.com)

Two realities make this urgent for engineering orgs. First, developer laptops are stacked with secrets: cloud profiles, kubeconfigs, package registries, and SSH agents. Second, build agents often run with generous permissions for speed—exactly where a local EoP becomes a supply‑chain event. Patch these tiers first.

What about GitHub Copilot for JetBrains and PowerShell?

On the IDE side, CVE‑2025‑64671 allows command injection in the Copilot plug‑in for JetBrains IDEs. The vendor‑tracked range includes versions below 1.5.60‑243; update immediately and audit any IDE scripts or terminal integrations that may auto‑approve commands. Pair that with a quick scan of project‑local .idea and build scripts for surprises. (stack.watch)

For automation, CVE‑2025‑54100 involves PowerShell’s Invoke‑WebRequest—exactly the snippet many bootstrap scripts use to pull installers or artifacts. If you ingest remote content during provisioning, patch and also enforce TLS pinning or checksum verification (e.g., SHA‑256) in your scripts. (techradar.com)

The 48‑hour Patch Sprint (use this as your checklist)

This is the pragmatic route we run with clients when time is short and stakes are high.

Hour 0–6: prioritize the blast radius

1) Developer endpoints: Windows 11 23H2/24H2/25H2 laptops used for source code access, package publishing, or cloud admin. 2) Build and CI agents: self‑hosted runners, ephemeral build pools, and any WSL‑enabled hosts. 3) Privileged workstations: IT and SRE jump boxes, domain admin consoles, help desk kiosks. These are your “tier‑zero” this week.

Push December cumulative updates and the JetBrains Copilot plug‑in patch now, with restarts scheduled in the same change window. Don’t let “pending reboot” linger; the driver update won’t fully load otherwise.

Hour 6–18: verify, don’t assume

For Windows: check installed KBs per OS build. A quick sample mapping seen in Microsoft ecosystem trackers this week includes KB5071417 (Windows 11 23H2) and KB5072033 (Windows 11 24H2/25H2), plus server equivalents (KB5071542/KB5071547). Confirm via PowerShell: Get-HotFix | Where-Object {$_.HotFixID -match "507"}. (rapid7.com)

For the driver: verify cldflt.sys version post‑reboot and that the file timestamp aligns with December 2025 updates. For Copilot: in JetBrains, open Settings → Plugins → GitHub Copilot and confirm 1.5.60‑243 or later. For PowerShell: run $PSVersionTable, then cross‑check the cumulative update notes in your update management tool.

Hour 18–36: close the obvious gaps

– WSL and containers on Windows: rebuild images used by local builds; if your Dockerfiles curl scripts via PowerShell or bash, enforce checksums and pull through a controlled mirror.

– CI runners: reset the AMI/base image with the December KBs and pin the version. Immutable pools beat long‑lived patching every time.

– IDE hygiene: remove unused extensions and disable any plug‑ins that auto‑execute shell commands in terminals. If your org piloted “agentic IDE” features, lock them to a non‑privileged profile while vendors catch up on secure defaults. (tomshardware.com)

Hour 36–48: prove it worked

Run a spot audit of 10% of endpoints and 100% of build agents. Evidence to capture: installed KBs, cldflt.sys version, IDE plug‑in version, and that restarts occurred. Store results in your CMDB or asset inventory.

People also ask: quick answers we keep getting

Is CVE‑2025‑62221 being exploited now?

Yes. Multiple reputable trackers and incident‑response firms report in‑the‑wild exploitation, and it’s been added to CISA’s KEV catalog, which indicates confirmed attacker use. Patch now, especially on systems that host synced cloud files or heavy user activity. (expel.com)

Do I need to reboot?

Plan on it. Kernel‑mode filter drivers require restarts to load patched binaries. Treat “pending reboot” as “not patched.” Schedule one coordinated reboot window so you’re not herding cats all week.

Will my WAF protect me?

Not for CVE‑2025‑62221. This is a local privilege escalation; network controls don’t help if the host is already touched. WAF tuning can reduce exploit delivery for web‑facing apps, but you still must patch endpoints and servers. If you need to change WAF rules safely, see our guidance on shipping WAF updates without downtime. Ship WAF fixes without going down.

The developer reality: where teams get burned

Here’s where we’ve seen real issues during post‑patch reviews:

– Long‑lived build agents: Teams patch the workstation fleet but forget the golden image feeding CI pools. A stale image respawns unpatched runners for weeks.

– IDE plug‑ins drift: Developers update the IDE, not the extensions. Centralize baseline policies for Copilot and other assistants, and audit plug‑in versions monthly.

– Scripted bootstrap risk: “curl | powershell” or “iwr https://... | iex” patterns still exist in bootstrap scripts. They’re convenient, but that convenience is exactly what CVE‑2025‑54100 targets. Lock this down with checksums and signed packages. (techradar.com)

– WSL as a shadow environment: Developers may do privileged work inside WSL that touches Windows file systems and credentials. After patching Windows, also rebuild WSL distributions and containers to ensure consistency.

A simple framework to keep: Patch, Prove, Prevent

Borrow this for your runbooks. It’s short on ceremony and long on outcomes.

Patch

– Apply the December cumulative updates across Windows 11/Server tiers.

– Update GitHub Copilot for JetBrains to 1.5.60‑243+ and review IDE execution policies. (stack.watch)

– Replace (not just patch) images for CI, VDI pools, and lab machines to bake in the fixed state.

Prove

– Inventory evidence: KB IDs (e.g., KB5071417, KB5072033), driver versions, IDE plug‑in versions.

– Sample endpoints and all build agents; require screenshots or command output attached to tickets.

– Run a post‑patch hunt: look for suspicious service creations, unexpected admin group changes, and unsigned binaries in temp directories. Our 30‑day security roadmap shows how to structure this without drowning the team. 30‑day security roadmap.

Prevent

– Kill dangerous bootstrap patterns; enforce checksums and package signatures for any remote downloads.

– Use least privilege on build agents; split duties between fetch, build, and sign steps.

– Add monthly IDE and plug‑in baselines to your endpoint management, just like browsers.

Data points you can take to leadership

– 57 vulnerabilities fixed on December 10, 2025; three zero‑days, including one exploited (CVE‑2025‑62221). (tomsguide.com)

– CVE‑2025‑62221 targets cldflt.sys, enabling SYSTEM‑level escalation from low‑privilege access; KEV‑listed and observed in the wild. (expel.com)

– Copilot for JetBrains (CVE‑2025‑64671) is a command‑injection risk that can compromise developer environments if left unpatched. (cybersecurity-help.cz)

– Representative Windows KBs to look for after patching: KB5071417 (Win 11 23H2), KB5072033 (Win 11 24H2/25H2), KB5071542/KB5071547 (Server). (rapid7.com)

How to verify: commands we actually use

– Installed updates: Get-HotFix | Sort-Object InstalledOn | Select-Object -Last 5

– Driver version: Get-Item "C:\\Windows\\System32\\drivers\\cldflt.sys" | Select-Object Name, @{n='Version';e={$_.VersionInfo.FileVersion}}, LastWriteTime

– Copilot plug‑in: JetBrains → Settings → Plugins → GitHub Copilot; confirm 1.5.60‑243 or later. Document with a screenshot policy for proof.

If you’re juggling serverless and data backends while you patch, keep cost and reliability in check too. Our practical playbooks for AWS workflows can help you avoid cutting corners while you stabilize. See Database Savings Plans: the practical playbook and our serverless durability guide.

But there’s a catch: patching isn’t a silver bullet

Two limitations to keep in mind:

– Patching after compromise doesn’t remove persistence. If you suspect a foothold before the reboot, run endpoint response checks (scheduled tasks, Run keys, WMI subscriptions) and rotate developer credentials and SSH keys used during the exposure window.

– IDE ecosystems move fast. Even patched, AI‑assisted IDEs can automate unsafe sequences if guardrails are loose. Disable auto‑execution features that spawn shells, and add a basic allowlist for build tools until you can roll out stricter profiles. (tomshardware.com)

Zooming out: build a security rhythm your teams can keep

Month after month, the same pattern repeats—EoP + RCE + a handful of “developer environment” bugs. So make Patch Tuesday a two‑day ritual with the framework above, then dedicate day three to detection and hardening. We’ve used a similar cadence on web stacks, too: when Next.js had its critical React Server Components flaw, the teams that won were the ones that patched fast, proved it, and hardened controls the same week. If you missed that story, here’s our Next.js CVE‑2025‑66478: Patch, Prove, Harden breakdown.

If you want help turning this into a repeatable, managed process—patching, verification, and a light threat‑hunt—we do that for engineering‑heavy companies every month. See our services or talk with us.

What to do next (today and this week)

– Today (December 13, 2025): push December cumulative updates to developer endpoints, build agents, and admin workstations; schedule reboots and confirm completion.

– Update JetBrains GitHub Copilot plug‑in to 1.5.60‑243+ and disable any auto‑approve command settings. Audit other IDE plug‑ins you don’t use.

– Rebuild CI images with patched baselines; pin AMI/container tags so old runners stop respawning.

– Add checksum/signature enforcement to any Invoke-WebRequest or curl downloads used in bootstrap scripts.

– Capture evidence: KBs, driver version, plug‑in version, reboot timestamps. Store it in your asset system.

– This week: run a light hunt on tier‑zero endpoints for suspicious persistence. If you need a phased plan, borrow steps from our Verify, Detect, Harden guide.

Final thought

Patching is the starting whistle, not the finish line. December 2025 Patch Tuesday gives you everything you need to close real risk—kernel EoP, IDE command‑injection, and brittle automation paths—if you act with speed and verification. Run the 48‑hour sprint, collect proof, and leave fewer places for attackers to hide next month.