CVE-2026-49797: Windows 10 1607 Buffer Overflow Flaw

CVE-2026-49797 Overview

CVE-2026-49797 is a heap-based buffer overflow [CWE-122] in the Windows New Technology File System (NTFS) driver. The flaw allows an unauthorized local attacker to execute arbitrary code on the affected system when a user interacts with a crafted file or volume. Microsoft published the advisory on 2026-07-14, and it affects a broad range of Windows client and Windows Server versions still in mainstream support. Successful exploitation requires local access and user interaction, but yields high impact to confidentiality, integrity, and availability.

Critical Impact
Attackers who convince a user to mount or open a crafted NTFS volume can corrupt heap memory in kernel or driver context and execute arbitrary code on the local host.

Affected Products

Microsoft Windows 10 (versions 1607, 1809, 21H2, 22H2) across x86, x64, and ARM64
Microsoft Windows 11 (versions 24H2, 25H2, 26H1) across x64 and ARM64
Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-07-14 - CVE-2026-49797 published to the National Vulnerability Database (NVD)
2026-07-14 - Microsoft publishes the Microsoft CVE-2026-49797 Update advisory
2026-07-16 - Last updated in the NVD database

Technical Details for CVE-2026-49797

Vulnerability Analysis

The vulnerability resides in the NTFS driver's handling of on-disk file system structures. When the driver parses attributes from a maliciously crafted NTFS volume, it writes past the bounds of a heap allocation. This corruption can overwrite adjacent kernel pool objects and, when combined with a controlled allocation layout, provides a path to arbitrary code execution in a privileged context. The attack requires local access and user interaction, typically achieved by convincing a user to open, mount, or browse a crafted virtual hard disk (VHD/VHDX) or removable volume.

Root Cause

The root cause is classified as a heap-based buffer overflow [CWE-122]. The NTFS driver allocates a destination buffer using size assumptions derived from untrusted on-disk metadata. When attribute lengths, run lists, or record offsets exceed those assumptions, the driver copies more data than the buffer can hold, corrupting adjacent heap memory.

Attack Vector

The attack vector is local and requires user interaction. A common exploitation path involves distributing a crafted .vhd or .vhdx file through email, download links, or removable media. When the user double-clicks the file, Windows automatically mounts it and the NTFS driver parses its metadata, triggering the overflow. Since parsing occurs in a privileged driver context, successful exploitation can yield SYSTEM-level code execution.

// No public proof-of-concept code is available for CVE-2026-49797.
// The vulnerability is triggered by NTFS metadata parsing on a
// crafted volume; refer to the Microsoft advisory for details.

Detection Methods for CVE-2026-49797

Indicators of Compromise

Unexpected mounting of .vhd or .vhdx files from user download or temp directories
Kernel-mode crashes or bugchecks referencing ntfs.sys shortly after volume mount events
Creation of new SYSTEM-context processes immediately following a file mount or removable media insertion

Detection Strategies

Monitor Windows event logs for VHDMP and Disk mount events originating from non-standard file paths
Alert on ntfs.sys crashes and pool corruption bugchecks (for example, BAD_POOL_HEADER, KERNEL_MODE_HEAP_CORRUPTION) recorded in Event ID 1001
Correlate volume mount events with subsequent privilege escalation or unusual child process creation from explorer.exe or dllhost.exe

Monitoring Recommendations

Track file writes and mounts of virtual disk images across endpoints using EDR telemetry
Baseline normal use of virtual hard disk files in your environment and alert on deviations
Ingest Windows kernel and driver crash telemetry into the security data lake for retrospective hunting

How to Mitigate CVE-2026-49797

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-49797 advisory to all affected Windows client and Server systems
Prioritize patching on multi-user systems, terminal servers, and endpoints where users routinely handle untrusted files
Restrict the ability of standard users to mount virtual disk images from untrusted sources

Patch Information

Microsoft has released security updates addressing CVE-2026-49797 for all supported affected products, including Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), and Windows Server 2012 through 2025. Consult the Microsoft Security Response Center advisory for the specific KB article and package that matches each Windows build and architecture.

Workarounds

Block execution and automatic mounting of .vhd and .vhdx files delivered via email or web downloads using attachment filters and Group Policy
Disable the Virtual Disk service on systems that do not require virtual disk mounting functionality
Enforce Attack Surface Reduction rules to block untrusted removable media and script-based volume mounting

bash

# Example: disable the Virtual Disk service on systems that do not need it
sc.exe config vds start= disabled
sc.exe stop vds

# Example: block .vhdx files in a Group Policy File System Access rule
# (adapt to your endpoint management tooling)
New-Item -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Explorer' -Force
Set-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\Explorer' \
  -Name 'NoAutoplayfornonVolume' -Value 1 -Type DWord