CVE-2025-62221: Windows 10 Privilege Escalation Flaw

CVE-2025-62221 Overview

CVE-2025-62221 is a use-after-free vulnerability in the Windows Cloud Files Mini Filter Driver that allows an authorized attacker to elevate privileges locally. This kernel-level vulnerability affects a wide range of Microsoft Windows operating systems, including both client and server editions. The Cloud Files Mini Filter Driver (cldflt.sys) is a critical Windows component responsible for managing cloud file synchronization and placeholder files used by OneDrive and other cloud storage providers.

Critical Impact

This vulnerability is actively exploited in the wild and has been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. Local attackers with low-privilege access can leverage this flaw to gain SYSTEM-level privileges, enabling complete system compromise.

Affected Products

• Microsoft Windows 10 1809 (x86 and x64)
• Microsoft Windows 10 21H2
• Microsoft Windows 10 22H2
• Microsoft Windows 11 23H2
• Microsoft Windows 11 24H2
• Microsoft Windows 11 25H2
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022
• Microsoft Windows Server 2022 23H2
• Microsoft Windows Server 2025

Discovery Timeline

• 2025-12-09 - CVE-2025-62221 published to NVD
• 2025-12-10 - Last updated in NVD database

Technical Details for CVE-2025-62221

Vulnerability Analysis

The vulnerability exists within the Windows Cloud Files Mini Filter Driver (cldflt.sys), a kernel-mode file system filter driver that handles cloud file operations. Use-after-free vulnerabilities occur when a program continues to reference memory after it has been freed, potentially allowing an attacker to manipulate the freed memory to gain control of program execution.

In the context of this vulnerability, the Cloud Files Mini Filter Driver fails to properly manage object lifetimes during certain file operations. When specific sequences of cloud file operations are performed, the driver may continue to reference deallocated memory structures. An attacker with local access can craft a series of operations that trigger this condition, ultimately corrupting kernel memory structures to escalate privileges from a standard user context to SYSTEM level.

The local attack vector requires the attacker to already have code execution on the target system, but the low attack complexity and no user interaction requirements make this an attractive target for post-exploitation privilege escalation. The vulnerability affects the confidentiality, integrity, and availability of the system, as successful exploitation grants complete control over the compromised host.

Root Cause

The root cause of CVE-2025-62221 is improper memory management within the Cloud Files Mini Filter Driver (CWE-416: Use After Free). The driver fails to properly validate and manage the lifecycle of internal data structures during cloud file synchronization operations. When certain race conditions or edge cases occur during file placeholder operations, the driver continues to use pointers to memory regions that have been freed, leading to undefined behavior that can be exploited for privilege escalation.

Attack Vector

The exploitation of this vulnerability follows a local privilege escalation attack pattern:

1. Initial Access: The attacker must first gain local code execution on the target Windows system, typically as a low-privileged user
2. Trigger Condition: The attacker performs a series of crafted cloud file operations that manipulate the Cloud Files Mini Filter Driver
3. Memory Corruption: By timing operations precisely, the attacker triggers the use-after-free condition, causing the driver to reference freed memory
4. Privilege Escalation: The attacker leverages kernel memory corruption to elevate from a standard user context to SYSTEM-level privileges
5. Complete Compromise: With SYSTEM privileges, the attacker can perform any action on the system including accessing sensitive data, installing malware, or moving laterally within the network

The vulnerability is particularly concerning because it targets a kernel-mode driver, making successful exploitation extremely powerful. The attacker gains complete control over the operating system, bypassing all user-level security controls.

Detection Methods for CVE-2025-62221

Indicators of Compromise

• Unusual process activity with elevated privileges originating from low-privilege user sessions
• Suspicious access patterns to cloud file placeholders or the cldflt.sys driver
• Kernel crash dumps referencing the Cloud Files Mini Filter Driver
• Evidence of privilege escalation tools or memory exploitation frameworks on the system
• Anomalous system calls targeting the cloud files subsystem

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions to monitor for kernel-mode exploitation attempts
• Enable Windows Defender Exploit Guard with Attack Surface Reduction (ASR) rules
• Monitor for suspicious process creation chains where low-privilege processes spawn high-privilege children
• Implement behavioral detection rules for use-after-free exploitation patterns in kernel drivers
• Configure SentinelOne Singularity to detect and block privilege escalation attempts targeting Windows kernel components

Monitoring Recommendations

• Enable verbose logging for Windows kernel events and driver operations
• Monitor for unusual activity involving cldflt.sys and related cloud file components
• Implement real-time alerting for privilege escalation events on critical systems
• Review Windows Event Logs for signs of kernel exploitation or driver crashes
• Deploy network segmentation to limit lateral movement if a system is compromised

How to Mitigate CVE-2025-62221

Immediate Actions Required

• Apply the latest Microsoft security patches immediately as this vulnerability is actively exploited
• Prioritize patching systems accessible to untrusted users or in multi-tenant environments
• Audit systems for signs of compromise before and after patching
• Implement application whitelisting to limit execution of unauthorized code
• Review and restrict local user privileges following the principle of least privilege

Patch Information

Microsoft has released security updates to address CVE-2025-62221. Organizations should apply the relevant patches from the Microsoft Security Response Center advisory for all affected systems. Given this vulnerability's inclusion in the CISA Known Exploited Vulnerabilities Catalog, federal agencies and organizations following CISA guidance should apply patches within the mandated timeframe.

Patches are available for:

• Windows 10 versions 1809, 21H2, and 22H2
• Windows 11 versions 23H2, 24H2, and 25H2
• Windows Server 2019, 2022, 2022 23H2, and Server 2025

Workarounds

• Restrict local access to systems where patching cannot be immediately performed
• Consider temporarily disabling cloud file synchronization features on high-value targets if business operations permit
• Implement enhanced monitoring for signs of exploitation on systems pending patches
• Use Windows Defender Credential Guard and other virtualization-based security features to limit the impact of privilege escalation
• Deploy network-level isolation for vulnerable systems until patches can be applied

# Verify Cloud Files Mini Filter Driver status
sc query cldflt

# Check current patch level (PowerShell)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10

# Temporarily stop cloud file services if mitigation is required (may impact OneDrive)
net stop CldFlt