CVE-2026-62713: Windows 10 1809 Privilege Escalation Flaw

CVE-2026-62713 Overview

CVE-2026-62713 is a heap-based buffer overflow [CWE-122] in the Windows Cloud Files Mini Filter Driver (cldflt.sys). An authorized local attacker can trigger the overflow to corrupt kernel memory and elevate privileges to SYSTEM. The flaw affects a broad range of Windows client and server releases, including Windows 10, Windows 11, and Windows Server 2019 through 2025. Microsoft published the advisory on 2026-08-11 and updated it on 2026-08-13. Exploitation requires local access and low privileges, and it does not require user interaction. No public proof-of-concept or in-the-wild exploitation has been reported at the time of publication.

Critical Impact
Successful exploitation grants kernel-level code execution, allowing an attacker to escape user-mode restrictions, disable security controls, and take full control of the affected host.

Affected Products

Microsoft Windows 10 (versions 1809, 21H2, 22H2) on x86, x64, and ARM64
Microsoft Windows 11 (versions 23H2, 24H2, 25H2, 26H1) on x64 and ARM64
Microsoft Windows Server 2019, Windows Server 2022, and Windows Server 2025

Discovery Timeline

2026-08-11 - CVE-2026-62713 published to NVD and Microsoft advisory released
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-62713

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 points, placeholder files, and cloud-sync IOCTLs on behalf of user-mode sync engines. A heap-based buffer overflow in this driver allows a local attacker with standard user privileges to write outside the bounds of a pool allocation. Because the overflow occurs inside a kernel filter driver, corruption of adjacent pool memory can be steered into arbitrary kernel read/write and, ultimately, code execution in ring 0.

Root Cause

The issue is classified under [CWE-122] Heap-based Buffer Overflow. The driver allocates a kernel pool buffer sized according to attacker-influenced input, then copies data into that buffer without correctly validating the destination length against the actual copy size. When the computed length is smaller than the data written, adjacent pool objects are overwritten. Microsoft has not published the specific field or IOCTL involved.

Attack Vector

An attacker running code as a standard user issues crafted requests to the Cloud Files driver, either through the documented cloud filter API (CfConnectSyncRoot, CfReportProviderProgress, and related calls) or by sending IOCTLs directly to the driver device object. The malicious request contains parameters that cause the vulnerable code path to under-allocate a heap buffer while copying attacker-controlled data of a larger size. The resulting pool corruption is shaped to overwrite kernel objects and pivot to SYSTEM-level execution. The attack vector is local (AV:L), and no user interaction is required.

No verified public exploit code is available. See the Microsoft CVE-2026-62713 Advisory for vendor technical details.

Detection Methods for CVE-2026-62713

Indicators of Compromise

Unexpected loads or crashes of cldflt.sys recorded in System event logs or WER crash dumps.
Standard user processes opening handles to \Device\CldFlt and issuing unusual DeviceIoControl sequences immediately before a privilege change.
New SYSTEM-level processes spawned from parents running under a non-privileged user token shortly after Cloud Files activity.

Detection Strategies

Hunt for unsigned or unusual binaries interacting with the Cloud Files driver interface, especially from user-writable directories such as %TEMP% and %APPDATA%.
Correlate kernel bugchecks referencing cldflt.sys (BAD_POOL_HEADER, KERNEL_MODE_HEAP_CORRUPTION) with recent process creation events on the same host.
Alert on token manipulation and integrity-level changes on processes that did not start elevated, a common post-exploitation signal for local privilege escalation.

Monitoring Recommendations

Ingest Sysmon Event IDs 1, 10, and 11 alongside Windows kernel event logs into a central data lake for correlation across hosts.
Track patch state of cldflt.sys across the fleet and flag endpoints running pre-patch file versions.
Baseline legitimate Cloud Files consumers (OneDrive, third-party sync providers) and alert on any other process invoking cloud filter APIs.

How to Mitigate CVE-2026-62713

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-62713 Advisory to all affected Windows 10, Windows 11, and Windows Server systems.
Prioritize patching multi-user systems, jump hosts, and VDI infrastructure where local privilege escalation has the highest blast radius.
Restrict interactive and remote logon rights for standard users on servers that do not require them.

Patch Information

Microsoft has released cumulative updates addressing CVE-2026-62713 for Windows 10 1809/21H2/22H2, Windows 11 23H2/24H2/25H2/26H1, and Windows Server 2019/2022/2025. Refer to the vendor advisory for the specific KB article and file version of cldflt.sys that corresponds to each supported build.

Workarounds

If patching must be delayed, disable the Cloud Files Filter Driver on systems that do not use OneDrive Files On-Demand or other cloud sync providers by stopping the CldFlt service and setting its start type to disabled.
Uninstall or disable OneDrive on servers and administrative workstations where it is not required for business operations.
Enforce application control (Windows Defender Application Control or AppLocker) to block untrusted binaries from executing in user-writable paths, reducing the ability to deliver an exploit.

bash

# Temporarily disable the Cloud Files Mini Filter Driver (requires reboot)
# Only use on systems that do not depend on OneDrive Files On-Demand
sc.exe config CldFlt start= disabled
sc.exe stop CldFlt