CVE-2025-62454 Overview
CVE-2025-62454 is a heap-based buffer overflow [CWE-122] in the Windows Cloud Files Mini Filter Driver (cldflt.sys). An authenticated local attacker can trigger the overflow to corrupt kernel heap memory and elevate privileges to SYSTEM. Microsoft addressed the flaw in the December 2025 security update cycle.
The vulnerability affects supported Windows 10, Windows 11, and Windows Server releases. Exploitation requires local access and low privileges, but no user interaction. Successful exploitation yields full confidentiality, integrity, and availability impact on the target host.
Critical Impact
A low-privileged local user can execute code in kernel context, taking full control of the affected Windows host and defeating standard user-mode security boundaries.
Affected Products
- Microsoft Windows 10 (1809, 21H2, 22H2)
- Microsoft Windows 11 (23H2, 24H2, 25H2)
- Microsoft Windows Server 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-12-09 - CVE-2025-62454 published to NVD alongside Microsoft's security update
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-62454
Vulnerability Analysis
The Cloud Files Mini Filter Driver (cldflt.sys) implements the kernel-mode component of the Windows Cloud Files API, which backs OneDrive Files On-Demand and other cloud sync providers. The driver processes reparse point data and placeholder metadata supplied through user-mode IOCTLs and filter callbacks.
A heap-based buffer overflow occurs when the driver allocates a kernel pool buffer using one size value while copying attacker-controlled data using a larger, unvalidated length. The out-of-bounds write corrupts adjacent pool memory. Because the corruption happens in kernel space, an attacker can groom the pool to overwrite kernel objects and hijack control flow, resulting in local privilege escalation from a standard user to SYSTEM.
Exploitation is local only and requires the attacker to already hold an authenticated session on the target. No user interaction is needed.
Root Cause
The root cause is missing or incorrect length validation on a size field consumed by the driver's cloud placeholder handling logic. The driver trusts a caller-supplied length when copying into a fixed-size pool allocation, satisfying the classic [CWE-122] heap-based buffer overflow pattern.
Attack Vector
An attacker executes code as a standard user on the target host and issues crafted requests to the Cloud Files filter driver through supported user-mode interfaces such as DeviceIoControl calls or CfApi operations. The malformed request triggers the overflow inside cldflt.sys, corrupts kernel pool memory, and enables privilege escalation.
No public proof-of-concept exploit is listed at time of publication. See the Microsoft Security Update CVE-2025-62454 advisory for vendor detail.
Detection Methods for CVE-2025-62454
Indicators of Compromise
- Unexpected loading or crashes of cldflt.sys in System event logs or WER reports
- Kernel bugchecks referencing pool corruption on hosts where OneDrive or third-party cloud sync clients are used
- New processes running as NT AUTHORITY\SYSTEM spawned from a standard user session shortly after Cloud Files API activity
Detection Strategies
- Alert on token-manipulation and parent-child anomalies where a medium-integrity user process is followed by a SYSTEM-integrity child
- Correlate Microsoft-Windows-CloudFilters operational log entries with subsequent kernel-mode faults
- Deploy behavioral endpoint detection that identifies kernel privilege-escalation primitives such as pool grooming and token swapping
Monitoring Recommendations
- Ensure Windows patch levels for December 2025 are inventoried across all Windows 10, 11, and Server hosts
- Monitor for repeated cldflt.sys faults or DRIVER_VERIFIER_DETECTED_VIOLATION events on endpoints
- Track unexpected installation or execution of cloud-sync client binaries on servers where they are not authorized
How to Mitigate CVE-2025-62454
Immediate Actions Required
- Apply the December 2025 Microsoft security update for every affected Windows 10, Windows 11, and Windows Server SKU listed in the advisory
- Prioritize multi-user hosts, jump servers, and VDI infrastructure where local privilege escalation has the highest blast radius
- Audit local account inventories and remove unnecessary interactive logon rights to reduce the pool of potential attackers
Patch Information
Microsoft released fixes as part of the December 2025 Patch Tuesday cycle. Consult the Microsoft Security Update CVE-2025-62454 guide for the specific KB article that corresponds to each Windows build in scope.
Workarounds
- No official workaround is published by Microsoft; patching is the required remediation
- On systems that do not require cloud file sync, disabling the CldFlt service and removing OneDrive reduces exposure to the vulnerable driver
- Enforce application control (WDAC or AppLocker) to block untrusted binaries that could stage a local exploit
# Query the Cloud Files filter driver state on a Windows host
sc.exe query CldFlt
# Verify December 2025 cumulative update is installed (example for Windows 11)
wmic qfe list brief /format:table | findstr /I "KB"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
