CVE-2026-3006: Kernel Race Condition Privilege Escalation

CVE-2026-3006 Overview

CVE-2026-3006 is a race condition vulnerability [CWE-362] that can trigger a kernel heap overflow in the affected software. The references point to WinFsp release v2.2B1, indicating the Windows File System Proxy driver is the impacted component. Successful exploitation allows a local attacker with low privileges to escalate to SYSTEM-level access on the affected host. The flaw is tracked in CSA Security Alert AL-2026-043 and was published to the National Vulnerability Database on April 27, 2026.

Critical Impact
A local attacker who wins the race window can corrupt kernel heap memory and obtain SYSTEM privileges, fully compromising the affected Windows host.

Affected Products

WinFsp (Windows File System Proxy) kernel driver
Versions prior to v2.2B1 (per vendor release notes)
Windows hosts running vulnerable WinFsp installations

Discovery Timeline

2026-04-27 - CVE-2026-3006 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-3006

Vulnerability Analysis

The vulnerability is a race condition [CWE-362] in the WinFsp kernel driver. Concurrent operations access a shared kernel object without proper synchronization. When two threads interleave at the unprotected code path, the driver writes beyond an allocated kernel pool buffer. This produces a kernel heap overflow inside the Windows non-paged or paged pool. The corrupted pool memory can be shaped to overwrite adjacent kernel objects, function pointers, or token structures. The attack vector is local and requires low privileges, but the attack complexity is high because the attacker must reliably win a narrow timing window.

Root Cause

The root cause is missing or insufficient locking around a shared resource in the WinFsp driver. A time-of-check to time-of-use (TOCTOU) gap permits two threads to operate on the same kernel allocation simultaneously. One thread frees or resizes the buffer while another writes to it, producing the overflow condition.

Attack Vector

An authenticated local user spawns multiple threads issuing concurrent I/O requests against the WinFsp driver. By repeatedly triggering the racy code path, the attacker eventually corrupts adjacent pool memory. Targeted overwrites of kernel structures, such as process tokens, replace the attacker's token with one belonging to SYSTEM. The vulnerability is not exploitable remotely and requires no user interaction.

No public proof-of-concept exploit is available. See the GitHub WinFsp Release v2.2B1 notes and the CSA Security Alert AL-2026-043 for additional technical context.

Detection Methods for CVE-2026-3006

Indicators of Compromise

Unexpected SYSTEM-level child processes spawned from a low-privilege user session interacting with WinFsp-mounted volumes.
Kernel bug checks (BSOD) referencing pool corruption, such as BAD_POOL_HEADER (0x19) or DRIVER_VERIFIER_DETECTED_VIOLATION, on hosts running vulnerable WinFsp builds.
Presence of WinFsp driver binaries with versions earlier than v2.2B1 on production endpoints.

Detection Strategies

Inventory all hosts running WinFsp and verify the driver version against v2.2B1 or later using endpoint telemetry.
Enable Driver Verifier with pool tracking on test systems to surface heap corruption originating in the WinFsp driver.
Hunt for processes with sudden token elevation, particularly user processes whose effective SID changes to S-1-5-18 (SYSTEM) without a legitimate elevation path.

Monitoring Recommendations

Forward Windows kernel crash dumps and Event ID 1001 (BugCheck) entries to a centralized SIEM for triage.
Monitor process creation events (Event ID 4688 / Sysmon Event ID 1) for SYSTEM processes parented by interactive user sessions.
Track loading of the WinFsp driver image and correlate against the approved patched version baseline.

How to Mitigate CVE-2026-3006

Immediate Actions Required

Upgrade all WinFsp installations to release v2.2B1 or later as published on the vendor's GitHub releases page.
Restrict local interactive logon on servers where WinFsp is installed to reduce the attack surface for local privilege escalation.
Audit which applications depend on WinFsp and coordinate patch testing with those application owners before broad deployment.

Patch Information

The vendor fix is delivered in the WinFsp v2.2B1 release. Administrators should download the signed installer, validate the package signature, and deploy through standard software distribution tooling. Refer to the CSA Security Alert AL-2026-043 for advisory details.

Workarounds

Uninstall WinFsp on hosts where it is not actively required until the patch can be applied.
Limit access to WinFsp-backed filesystems to trusted, high-integrity user accounts only.
Enable Windows Defender Application Control or AppLocker policies that block unauthorized local binaries from launching, reducing the practical ability of an attacker to stage exploit code.

bash

# Verify installed WinFsp driver version on Windows (PowerShell)
Get-ItemProperty -Path 'HKLM:\SOFTWARE\WOW6432Node\WinFsp' |
    Select-Object -Property Version

# Confirm the driver file version
Get-Item 'C:\Program Files (x86)\WinFsp\bin\winfsp-x64.sys' |
    Select-Object -ExpandProperty VersionInfo