CVE-2025-50170 Overview
CVE-2025-50170 is a local privilege escalation vulnerability in the Windows Cloud Files Mini Filter Driver (cldflt.sys). The flaw stems from improper handling of insufficient permissions or privileges [CWE-280], allowing an authorized local attacker to elevate privileges on affected Windows systems. Microsoft assigned this vulnerability a CVSS 3.1 base score of 7.8. The issue affects a broad range of Windows client and server releases, including Windows 10, Windows 11, and Windows Server 2019 through 2025. Successful exploitation grants attackers high impact on confidentiality, integrity, and availability, effectively enabling SYSTEM-level code execution from a standard user context.
Critical Impact
A locally authenticated attacker can escalate privileges to SYSTEM, gaining full control of the affected Windows host and bypassing standard user isolation boundaries.
Affected Products
- Microsoft Windows 10 (1809, 21H2, 22H2)
- Microsoft Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-08-12 - CVE-2025-50170 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-50170
Vulnerability Analysis
The Windows Cloud Files Mini Filter Driver (cldflt.sys) supports the Cloud Files API used by OneDrive and other cloud sync providers. It brokers filesystem operations between user-mode sync engines and the kernel I/O stack. The driver runs in kernel mode and must validate that requesting processes hold sufficient rights before executing privileged operations on placeholder files, reparse points, and sync-root registrations.
CVE-2025-50170 arises because the driver fails to correctly enforce permission checks on one or more of these code paths. An authorized user who can interact with the driver's IOCTL or filter-callback interface can trigger operations that should be restricted to higher-privileged callers. The result is arbitrary manipulation of kernel-managed state from a low-privileged context.
Root Cause
The root cause maps to CWE-280: Improper Handling of Insufficient Permissions or Privileges. The driver assumes that a caller reaching a particular code path holds the required token privileges or object access rights. When those checks are missing or short-circuited, a standard user can invoke functionality reserved for administrators or SYSTEM.
Attack Vector
Exploitation requires local access and low privileges. No user interaction is needed. An attacker with a valid session sends crafted requests to cldflt.sys, typically through documented cloud-files APIs or direct device I/O, to reach the vulnerable code path. Successful exploitation yields SYSTEM privileges on the local host. Microsoft's advisory does not indicate active exploitation, and no public proof-of-concept is available at this time. See the Microsoft CVE-2025-50170 Advisory for vendor-provided technical context.
Detection Methods for CVE-2025-50170
Indicators of Compromise
- Unexpected loads or crashes of cldflt.sys recorded in the Windows System event log or WER reports.
- Processes owned by standard users spawning child processes with SYSTEM integrity levels shortly after interacting with cloud files APIs.
- Anomalous creation or manipulation of reparse points, placeholder files, or sync roots outside of legitimate OneDrive or cloud sync workflows.
Detection Strategies
- Monitor kernel-mode telemetry for token elevation events where the parent process runs as a non-administrative user.
- Correlate cldflt.sys I/O activity with subsequent privileged process creation using EDR process-lineage data.
- Alert on installation or use of tools that interact directly with the Cloud Files Mini Filter driver outside of known applications such as OneDrive.exe.
Monitoring Recommendations
- Ingest Windows Security event ID 4672 (special privileges assigned) and 4688 (process creation) into your SIEM and baseline normal behavior.
- Track patch compliance for the August 2025 Windows cumulative updates across all endpoints and servers.
- Enable kernel driver load auditing and review any non-Microsoft-signed filter drivers registered against the storage stack.
How to Mitigate CVE-2025-50170
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2025-50170 Advisory to all affected Windows and Windows Server versions.
- Prioritize patching multi-user systems, jump hosts, and terminal servers where local privilege escalation risk is highest.
- Audit local accounts and remove unnecessary interactive logon rights to reduce the population of users who can trigger the flaw.
Patch Information
Microsoft addressed CVE-2025-50170 through the August 2025 Patch Tuesday cumulative updates for Windows 10, Windows 11, and Windows Server 2019 through 2025. Administrators should deploy the corresponding KB update for each supported build via Windows Update, WSUS, or their preferred update management platform. Refer to the vendor advisory for KB numbers per SKU.
Workarounds
- No official workaround is documented by Microsoft; installing the security update is the supported remediation.
- Where patching is delayed, restrict interactive and remote-desktop access to trusted administrators only.
- Disable or uninstall cloud sync clients that depend on cldflt.sys on systems that do not require them, reducing exposure of the driver's attack surface.
# Verify the Cloud Files Mini Filter driver version on a Windows host
Get-Item C:\Windows\System32\drivers\cldflt.sys | Select-Object VersionInfo
# Confirm the August 2025 cumulative update is installed
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 10
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
