December usually arrives with a quieter security rhythm, and this year, Microsoft offered exactly that: a lighter Patch Tuesday to close 2025. Yet even with fewer vulnerabilities released, one actively exploited flaw stands out, and two critical Office issues remind CISOs why email remains one of the most sensitive areas in enterprise defense.

If you’re leading security strategy or simply navigating the steady stream of patch advisories, this month’s update brings both urgency and relief. You can fix what matters most, and then let your teams exhale after a long year. Analysts project that global end-user spending on information security will reach US$213 billion in 2025, up from US$193 billion in 2024.

Patch First: CVE-2025-62221 

The most urgent issue this month is the use-after-free vulnerability in the Windows Cloud Files Mini Filter. It enables SYSTEM-level access, which places it at the top of every patching list.

Key reasons to address this immediately:

  • It’s already under active exploitation.
  • SYSTEM-level impact gives attackers deep reach.
  • Cloud file components interact with many everyday workflows.
  • Microsoft highlighted it as a high-risk path.

When attackers are already using a vulnerability, response time becomes the most important factor.

Related Reading: Microsoft Threat Intelligence Update: How Midnight Blizzard Carried Out Spear-phishing using RDP Files

The Silent Ones: Two Office Preview Pane Vulnerabilities

This December also includes two critical Office vulnerabilities:

  • CVE-2025-62557
  • CVE-2025-62554

Both are use-after-free issues, and both can be triggered through the Preview Pane. This is where things get serious.

Preview Pane exploitation requires no active user interaction. The file only needs to appear in a viewable location. That’s why these issues sit high on CISO dashboards; they create quiet entry points that blend into normal email behavior.

66% of advanced phishing campaigns use document-based payloads” – Microsoft Digital Defense Report. 

Threat intelligence across 2025 showed continued growth in low-click or no-click attack methods. These two vulnerabilities reinforce that trend.

What This Patch Cycle Means for 2026 Planning

As teams plan next year’s security investments, this Patch Tuesday points to one area that consistently needs more attention: email security.

By 2026, 60% of organizations will adopt advanced email security solutions beyond Microsoft 365’s native controls. 

Several enterprise reports from 2025 showed:

  • Email remained the top initial access vector for targeted attacks.
  • Preview-based exploits gained traction as attackers adapted to safer user behavior.
  • Many organizations saw patching workloads rise by more than 20%.
  • Cloud file and sync components increasingly became part of attack paths.

With these data points in mind, strengthening email security filters, isolation layers, advanced scanning, and real-time behavioral detection becomes a meaningful priority for 2026. 

By 2025, the shift to cloud and AI is accelerating demand – many organizations now treat cybersecurity as a board-level concern: according to Gartner’s 2024 Board Survey, 93% of corporate boards see cyber-risk as a threat to stakeholder value.

Expert Commentary from Fortra’s Tyler Reguly

“Let’s end the year with a statistic that I find somewhat interesting. In 2025, Microsoft patched 1275 vulnerabilities. Which should mean roughly 106 vulnerabilities each month, yet December only saw 70 vulnerabilities when you include the third-party CNA vulnerabilities. If all things were equal, December should account for 8.3% of all CVEs fixed by Microsoft; instead, December only contains 5.5% of this year’s total CVEs. I suppose we can thank Microsoft for an early Christmas gift.

We’re ending the year with a vulnerability that is seeing active exploitation, the use-after-free vulnerability in the Windows Cloud Files Mini Filter (CVE-2025-62221). Given that this vulnerability is seeing active exploitation and could lead to SYSTEM-level access, this should be the priority for patching this month.

There are two vulnerabilities that Microsoft has rated as Critical this month, and it is probably more important that we discuss these than the two publicly disclosed vulnerabilities. For that reason, I would prioritize CVE-2025-62557 and CVE-2025-62554, a pair of use-after-free vulnerabilities in Office, over CVE-2025-54100 and CVE-2025-64671, command injection vulnerabilities in PowerShell and GitHub CoPilot for JetBrains. All 4 vulnerabilities are listed as less likely to be exploited, but the Office vulnerabilities list the Preview Pane as an attack vector, and I always find that one of the scariest attack vectors that can be listed. Vulnerabilities that don’t rely on user interaction are vulnerabilities that we want to pay attention to.

CISOs this month should remember that their admins have remediated (or at least reviewed) 1275 vulnerabilities from just Microsoft alone this year. It’s been a long, vulnerability-filled year for our security teams, and I’d imagine they’re tired. Thankfully, Microsoft provided this gift of a smaller Patch Tuesday without too many high-profile items… let your teams relax a little as we wrap up the year; there are enough other items to keep them busy without stressing over this Patch Tuesday release.

If I were in charge of all aspects of security for an enterprise as we wrap up the year and think about 2026 budgets, I’d probably be thinking about the two critical Office vulnerabilities that impact the Preview Pane and consider the email protections that I have in place and where I can make investments in 2026 to further improve the email security of my organization. Between “silent attacks” that utilize the preview pane, phishing, and all the other risks that come to us via email, it is one of the places where organizations can still do more to shore up their security posture and put themselves in a good place”. – Tyler Reguly, Associate Director, Security R&D, Fortra. 

Learn more about Fortra: Fortra Releases New AI Models, Threat Hunting, and Intelligence Features.

Conclusion 

This December Patch Tuesday may feel lighter, but its message is clear: act fast on the exploited flaw, reinforce defenses against silent email-based threats, and give security teams the breathing room they’ve earned. With focused attention on high-impact vulnerabilities and smarter planning for 2026, organizations can move into the new year more prepared and more resilient.

FAQs

1. Why should CVE-2025-62221 be patched first?

It is already being used by attackers and grants high-level access, making it the most urgent item this month.

2. Why are Office Preview Pane vulnerabilities significant?

They can be triggered when content appears in the Preview Pane, without requiring a user to fully open or interact with the file.

3. Should enterprises treat “exploitation less likely” vulnerabilities as high priority?

Yes, when the attack path involves automated preview features or common workflows.

4. What’s the main takeaway from December’s patch cycle for CISOs?

Strengthen email-based defenses and prioritize vulnerabilities that enable silent or low-interaction exploitation.

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