Brinztech Alert: December 2025 Patch Tuesday: 3 Zero-Days & Actively Exploited Windows Driver Vulnerability

Patch Tuesday Analysis: December 2025

The final Patch Tuesday of 2025 addresses a severe landscape of vulnerabilities across the enterprise stack. Security teams must prioritize CVE-2025-62221, a Windows driver vulnerability confirmed to be under active exploitation in the wild. Additionally, critical Remote Code Execution (RCE) flaws in Microsoft Outlook, SAP, and Fortinet appliances pose significant risks to network perimeters and user endpoints.

Brinztech Analysis:

• The Active Threat (CVE-2025-62221): This Elevation of Privilege (EoP) vulnerability affects the Windows Cloud Files Mini Filter Driver (cldflt.sys).
  • Risk: Attackers who already have limited access to a system (e.g., via malware or a compromised user account) can use this exploit to elevate their privileges to SYSTEM. This allows them to disable security tools, steal credentials, or deploy ransomware widely. Because it is actively exploited, patches must be deployed immediately (0-24 hour window).
• The “Zero-Click” Risks (Outlook/Office): Microsoft patched critical RCE vulnerabilities in Office and Outlook (CVE-2025-62554, 62557, 62562).
  • Vector: These flaws typically allow code execution via the “Preview Pane” or simply by opening a malicious email/document. This makes every employee inbox a potential entry point for attackers.
• Infrastructure Threats (Fortinet & Ivanti):
  • Fortinet (CVE-2025-59718 & 59719): Critical flaws in FortiManager/FortiAnalyzer. Attackers can potentially bypass authentication.
  • Ivanti (CVE-2025-10573): Another critical RCE in Ivanti Connect Secure (VPN), a favorite target for ransomware groups looking for initial access.

Key Cybersecurity Insights

This month’s update highlights the diversity of the modern attack surface:

• Driver-Based Attacks: The exploitation of the Cloud Files driver continues a trend of attackers abusing built-in Windows kernel drivers to bypass EDR (Endpoint Detection & Response) solutions.
• Supply Chain / ERP Risk: The critical SAP vulnerabilities (CVE-2025-42880, etc.) affect BusinessObjects and Commerce platforms. Exploiting these can lead to theft of proprietary business data or disruption of supply chains.
• Authentication Bypass: The Fortinet vulnerabilities are particularly dangerous because they involve SSO (Single Sign-On) mechanisms. If an attacker bypasses SSO, they gain administrative access without needing valid credentials.

Mitigation Strategies

Organizations must triage these updates based on risk of exploitation:

1. Immediate Action (0-24 Hours)

• Patch Windows Clients & Servers: prioritize the fix for CVE-2025-62221 across all assets.
• Fortinet Remediation: Patch FortiManager/FortiAnalyzer immediately. Workaround: If patching is not instantly possible, disable FortiCloud SSO functionality to mitigate the specific authentication bypass vector reported.

2. High Priority (24-48 Hours)

• Update Office 365 / Outlook: Ensure the “Click-to-Run” update channels are pushing the latest Office builds to users to close the RCE gaps (CVE-2025-62554).
• Patch Ivanti VPNs: Verify Ivanti Connect Secure gateways are updated to prevent perimeter breaches.

3. Standard Cycle (Week 1)

• SAP & Adobe: Apply patches to SAP BusinessObjects and Adobe Creative Cloud apps (Illustrator/After Effects) during standard maintenance windows, as these typically require local access or specific user interaction to exploit.

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