CVE-2026-50492: Windows ReFS Buffer Overflow Vulnerability

CVE-2026-50492 Overview

CVE-2026-50492 is a heap-based buffer overflow vulnerability in the Windows Resilient File System (ReFS). The flaw allows an unauthorized attacker with physical access to a target system to execute arbitrary code. The vulnerability is tracked under CWE-122 (Heap-based Buffer Overflow) and carries a CVSS 3.1 base score of 6.8. Microsoft published details of the issue on July 14, 2026 through the Microsoft Security Update Guide.

Critical Impact
Successful exploitation gives an attacker the ability to run code on the target system and compromise the confidentiality, integrity, and availability of data on ReFS-formatted volumes.

Affected Products

Microsoft Windows implementations that ship the Resilient File System (ReFS) driver
Windows client and server SKUs that expose ReFS volume mounting to external media
Refer to the Microsoft Security Update Guide for the authoritative list of affected builds

Discovery Timeline

2026-07-14 - CVE-2026-50492 published to NVD
2026-07-14 - Last updated in NVD database

Technical Details for CVE-2026-50492

Vulnerability Analysis

The vulnerability resides in the ReFS driver's handling of on-disk metadata structures. When Windows parses a maliciously crafted ReFS volume, the driver writes past the bounds of a heap-allocated buffer. This corruption occurs in kernel-mode code responsible for interpreting file system structures during volume mount or file access operations.

Because the corruption happens on the heap inside the kernel pool, an attacker can influence adjacent allocations to steer control flow. The end result is arbitrary code execution in the security context of the operating system. Impact scope is limited to the local host, but no authentication or user interaction is required once the attacker connects the malicious media.

Root Cause

The root cause is insufficient validation of length or offset fields inside ReFS on-disk data structures. The driver trusts attacker-controlled values when sizing a destination buffer or copying metadata, allowing a heap overflow classified as [CWE-122]. Vendor advisories from Microsoft do not disclose the specific structure or function affected.

Attack Vector

Exploitation requires physical access to the target machine. An attacker crafts a malicious ReFS-formatted volume, typically on removable storage such as a USB drive or external disk, and connects it to the victim system. When Windows attempts to mount or read the volume, the vulnerable ReFS parsing code triggers the overflow. Public proof-of-concept code is not available and no in-the-wild exploitation has been reported.

No verified exploit code is available. Microsoft's advisory does not include technical exploitation details. See the Microsoft Security Update Guide for vendor guidance.

Detection Methods for CVE-2026-50492

Indicators of Compromise

Unexpected mount events for ReFS-formatted removable media on endpoints that do not normally use ReFS volumes
Kernel-mode crashes or bug checks referencing refs.sys or refsv1.sys shortly after external storage is connected
New or anomalous kernel-level processes or driver loads following a physical device connection event

Detection Strategies

Monitor Windows event logs for Microsoft-Windows-Ntfs and ReFS driver errors correlated with removable media insertion
Alert on kernel bug check events (Event ID 1001) referencing ReFS components
Correlate USB or storage device insertion telemetry with subsequent process creation or privilege changes

Monitoring Recommendations

Enable USB device auditing and forward events to a centralized log platform for correlation
Track file system driver load events and volume mount operations across managed endpoints
Baseline the use of ReFS volumes in the environment so anomalous mounts stand out during triage

How to Mitigate CVE-2026-50492

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update Guide as soon as testing permits
Restrict physical access to endpoints and servers, particularly in shared or public environments
Disable or block unauthorized USB and external storage devices through group policy or endpoint controls

Patch Information

Microsoft has released a security update addressing CVE-2026-50492. Administrators should consult the Microsoft Security Update Guide to identify the specific KB article and build numbers that apply to their Windows versions and deploy the update through Windows Update, WSUS, or their standard patch management pipeline.

Workarounds

Enforce device control policies that block mounting of unknown or unapproved removable storage
Disable ReFS volume auto-mount on systems that do not require ReFS functionality
Apply BitLocker and physical security controls to reduce opportunities for an attacker to attach malicious media

bash

# Example: block removable storage write and execute via Group Policy registry keys
reg add "HKLM\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies" /v WriteProtect /t REG_DWORD /d 1 /f
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\RemovableStorageDevices" /v Deny_All /t REG_DWORD /d 1 /f