CVE-2026-50374 Overview
CVE-2026-50374 is a use-after-free vulnerability [CWE-416] in the Windows Cloud Files Mini Filter Driver (cldflt.sys). The flaw allows an authorized attacker with physical access to elevate privileges on affected Windows systems. Microsoft assigned this CVE a medium severity rating, reflecting the physical attack vector requirement that limits remote exploitation. Successful exploitation grants the attacker high impact on confidentiality, integrity, and availability of the target host. The vulnerability affects a broad range of Windows client and server releases, including Windows 10, Windows 11, and Windows Server 2019 through 2025.
Critical Impact
An authorized attacker with physical access can trigger a use-after-free in the Cloud Files Mini Filter Driver to gain elevated privileges on the affected Windows host.
Affected Products
- Microsoft Windows 10 (1809, 21H2, 22H2)
- Microsoft Windows 11 (24H2, 25H2, 26H1)
- Microsoft Windows Server 2019, 2022, and 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-50374 published to NVD
- 2026-07-20 - Last updated in NVD database
Technical Details for CVE-2026-50374
Vulnerability Analysis
The vulnerability resides in the Windows Cloud Files Mini Filter Driver, a kernel-mode component that mediates access to files managed by cloud sync providers such as OneDrive. The driver exposes I/O interfaces that user-mode components invoke to interact with placeholder and hydrated cloud files. A use-after-free condition [CWE-416] occurs when the driver dereferences an object after its backing memory has been released, enabling an attacker to influence the freed allocation.
Because the vulnerable code path executes in kernel context, controlled reuse of the freed object can lead to arbitrary kernel memory corruption. An authorized local user who successfully manipulates the object lifecycle can escalate from a standard user context to SYSTEM. The attack vector is scored as physical, indicating the exploit path requires direct interaction with the device rather than remote or network access.
Root Cause
The root cause is improper synchronization or reference counting on an object managed by cldflt.sys. The driver frees an allocation while another code path retains a stale pointer. Subsequent access to that pointer dereferences memory that may be reclaimed and controlled by the attacker.
Attack Vector
Exploitation requires an authenticated user with physical access to the target device. The attacker triggers a race or state transition in the Cloud Files driver to force premature deallocation of a tracked object. Reallocating the freed region with attacker-controlled data allows kernel pointer or function call hijacking, resulting in privilege escalation to SYSTEM. No user interaction from another account is required.
No public proof-of-concept exploit is available at the time of publication.
Detection Methods for CVE-2026-50374
Indicators of Compromise
- Unexpected bugchecks or kernel crashes referencing cldflt.sys in Windows Error Reporting or minidumps.
- Creation of new SYSTEM-level processes spawned from a session originally owned by a standard user.
- Anomalous loading, unloading, or reconfiguration of the Cloud Files Mini Filter Driver on endpoints without active OneDrive or cloud sync usage.
Detection Strategies
- Monitor kernel crash telemetry for faults in cldflt.sys following interactive logons or physical console activity.
- Correlate token elevation events (Event ID 4672) with the originating user session to identify unauthorized privilege transitions.
- Baseline expected Cloud Files driver activity on managed endpoints and alert on deviations from normal I/O patterns.
Monitoring Recommendations
- Ingest Windows Security, System, and WER logs into a centralized analytics platform to correlate driver faults with logon activity.
- Track physical logon events (Event IDs 4624 type 2 and 4778) on high-value systems and workstations exposed to unattended access.
- Enable kernel-mode driver auditing and file system minifilter telemetry where available.
How to Mitigate CVE-2026-50374
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-50374 Advisory to all affected Windows client and server builds.
- Prioritize patching for endpoints exposed to physical access such as kiosks, shared workstations, and unattended laptops.
- Verify that BitLocker or equivalent full-disk encryption is enforced with pre-boot authentication to raise the cost of physical attacks.
Patch Information
Microsoft has published guidance and security updates for this vulnerability through the Microsoft Security Response Center. Refer to the Microsoft CVE-2026-50374 Advisory for the specific Knowledge Base article, build numbers, and update packages applicable to each Windows release listed under Affected Products.
Workarounds
- Restrict physical access to affected systems using enclosures, port controls, and physical security policies.
- Disable or restrict the Cloud Files Mini Filter Driver on systems that do not use OneDrive or other cloud sync providers, where operationally acceptable.
- Enforce least privilege for interactive users and remove unnecessary local administrator rights to limit post-exploitation impact.
# Configuration example: verify Cloud Files driver status and patch level
sc.exe query cldflt
wmic qfe list brief | findstr /I "KB"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
