CVE-2025-62457: Windows 10 1809 Privilege Escalation Flaw

CVE-2025-62457 Overview

CVE-2025-62457 is an out-of-bounds read vulnerability in the Windows Cloud Files Mini Filter Driver (cldflt.sys). An authorized local attacker can exploit the flaw to elevate privileges on affected Windows systems. Microsoft published the advisory on December 9, 2025, and the issue affects a broad range of Windows client and server releases, including Windows 10, Windows 11, and Windows Server versions from 2019 through 2025. The weakness is classified under CWE-125: Out-of-bounds Read.

Critical Impact
Successful exploitation grants attackers elevated privileges on the local system, enabling full compromise of confidentiality, integrity, and availability.

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-2025-62457 published to NVD
2025-12-09 - Microsoft releases security update for CVE-2025-62457
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-62457

Vulnerability Analysis

The vulnerability resides in the Windows Cloud Files Mini Filter Driver, the kernel-mode component that backs the Cloud Files API used by OneDrive and other cloud sync providers. The driver reads data past the bounds of an allocated buffer when processing attacker-influenced input. An authorized user on the system can trigger this out-of-bounds read from user mode and leverage the resulting kernel-memory disclosure or corruption to escalate privileges.

Exploitation requires the attacker to already hold a valid local account, which lowers the barrier for post-compromise activity such as malware execution under a low-privilege user or a compromised service account. Because the flaw sits in a kernel-mode filter driver, successful exploitation yields SYSTEM-level access, allowing installation of persistence mechanisms, disabling of security tooling, and lateral movement.

Root Cause

The root cause is missing or insufficient bounds checking on a buffer accessed within cldflt.sys. When the driver processes a request routed through the Cloud Files filter, it reads memory beyond the intended range, exposing adjacent kernel data or corrupting driver state.

Attack Vector

The attack vector is local. An attacker with authenticated access invokes the vulnerable code path from user mode, likely through crafted I/O control requests or file operations against a cloud-backed placeholder. No user interaction is required beyond execution of the attacker's tool. Microsoft has not published exploit details, and no public proof-of-concept is currently available. See the Microsoft Security Update Guide for CVE-2025-62457 for vendor guidance.

The vulnerability manifests inside the Cloud Files Mini Filter Driver during buffer handling. Refer to the vendor advisory for authoritative technical details.

Detection Methods for CVE-2025-62457

Indicators of Compromise

Unexpected crashes, bug checks, or kernel memory faults referencing cldflt.sys in Windows Event Log or minidumps.
New or unknown processes running with SYSTEM privileges after being spawned by a standard user session.
Unusual invocation of Cloud Files APIs by processes that do not typically interact with OneDrive or cloud sync placeholders.

Detection Strategies

Monitor process ancestry for privilege transitions where a standard user token spawns a SYSTEM-integrity process.
Track loading and abnormal use of cldflt.sys through kernel telemetry and Sysmon Event ID 6 (driver loaded) and Event ID 1 (process create).
Correlate local logon events with subsequent token elevation to detect exploitation attempts against low-privilege accounts.

Monitoring Recommendations

Ingest Windows kernel and driver crash telemetry into a centralized SIEM for pattern analysis across the fleet.
Alert on repeated cldflt.sys faults from the same host or user, which may indicate exploit development or brute-force triggering.
Baseline normal Cloud Files activity per endpoint and flag deviations from processes outside OneDrive or approved sync clients.

How to Mitigate CVE-2025-62457

Immediate Actions Required

Apply the December 2025 Microsoft security update for CVE-2025-62457 to all affected Windows client and server systems.
Prioritize patching on multi-user systems, terminal servers, and endpoints where non-administrative users have interactive access.
Audit local accounts and remove unnecessary standard user privileges to reduce the population of potential attackers.

Patch Information

Microsoft released a security update on December 9, 2025 addressing the out-of-bounds read in cldflt.sys. Administrators should consult the Microsoft Security Update Guide for CVE-2025-62457 to identify the correct KB article for each Windows build and deploy via Windows Update, WSUS, or Microsoft Update Catalog.

Workarounds

No official workaround has been published by Microsoft; patching is the supported remediation.
Where patching must be delayed, restrict interactive and remote logon rights for non-administrative users on affected systems.
Disable the Cloud Files feature or the OneDrive sync client on systems that do not require cloud file placeholders, reducing reachable attack surface in cldflt.sys.

bash

# Verify installed updates on a Windows host
wmic qfe list brief /format:table

# Example: disable OneDrive sync client where cloud files are not required
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\OneDrive" /v DisableFileSyncNGSC /t REG_DWORD /d 1 /f