CVE-2026-50308: Windows 10 1607 NTFS RCE Vulnerability

CVE-2026-50308 Overview

CVE-2026-50308 is an integer underflow vulnerability [CWE-122] in the Windows NTFS file system driver. The flaw allows an unauthorized local attacker to execute code on affected systems by triggering a wraparound condition during NTFS metadata processing. Successful exploitation requires user interaction, typically the mounting or opening of a maliciously crafted NTFS volume or file.

Microsoft published the vulnerability on July 14, 2026, affecting a broad range of Windows client and server releases from Windows Server 2012 through Windows 11 25H2 and Windows Server 2025. The vulnerability carries a CVSS 3.1 score of 7.8 and can lead to full compromise of confidentiality, integrity, and availability on the local host.

Critical Impact
Local code execution through NTFS integer underflow enables attackers to escalate privileges and gain full control of the affected Windows host once a crafted volume or file is processed.

Affected Products

Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
Microsoft Windows 11 (24H2, 25H2, 26H1)
Microsoft Windows Server 2012, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-07-14 - CVE-2026-50308 published to NVD and addressed in Microsoft security update
2026-07-16 - Last updated in NVD database

Technical Details for CVE-2026-50308

Vulnerability Analysis

The vulnerability resides in the NTFS driver's handling of size or length fields during file system metadata parsing. An integer underflow occurs when a value is decremented or subtracted below zero, wrapping around to a large unsigned value. That wrapped value is then used in subsequent length calculations or memory allocations, producing an undersized buffer relative to the data written.

Because CWE-122 (Heap-based Buffer Overflow) is associated with this issue, the underflow ultimately drives an out-of-bounds write on the heap inside the NTFS kernel component. Kernel-mode heap corruption of this class typically allows an attacker to overwrite adjacent pool structures and hijack control flow at the highest privilege level.

Root Cause

The root cause is missing validation of arithmetic operations on unsigned length or offset fields parsed from NTFS on-disk structures. When a crafted value causes a subtraction to underflow, the resulting large integer bypasses subsequent bounds checks and is used to size or index into a kernel pool allocation.

Attack Vector

Exploitation is local and requires user interaction. An attacker crafts a malicious NTFS volume, VHD, or ISO image and induces a user to mount or open it. When the NTFS driver parses the crafted metadata, the underflow triggers heap corruption in kernel context. Common delivery paths include removable media, downloaded disk images, and mounted virtual hard disks from phishing lures.

No public proof-of-concept or in-the-wild exploitation has been reported. The EPSS probability at publication is 0.36%.

Detection Methods for CVE-2026-50308

Indicators of Compromise

Unexpected mounting of VHD, VHDX, or ISO files originating from email attachments, browser downloads, or removable media.
NTFS driver crashes, bugchecks referencing ntfs.sys, or Event ID 41/1001 kernel crash entries following disk image interaction.
Creation of new kernel-level processes or drivers immediately after a user opens an unknown disk image.

Detection Strategies

Monitor Windows Event Logs for Microsoft-Windows-Ntfs errors and kernel pool corruption bugchecks (BSOD codes such as 0x139 KERNEL_SECURITY_CHECK_FAILURE).
Alert on user-initiated mounts of disk image files via Mount-DiskImage, PowerShell, or Explorer double-click actions on attachments.
Deploy EDR behavioral rules that flag privilege escalation chains initiated shortly after disk image mount events.

Monitoring Recommendations

Track process ancestry when explorer.exe or mail clients spawn image-mounting activity followed by kernel-level anomalies.
Ingest kernel crash telemetry into a SIEM to correlate NTFS driver faults across the fleet.
Baseline expected sources of VHD and ISO mounts and alert on deviations, especially from user profile directories.

How to Mitigate CVE-2026-50308

Immediate Actions Required

Apply the July 2026 Microsoft security updates referenced in the Microsoft Security Update Guide for CVE-2026-50308 to all affected Windows client and server systems.
Prioritize patching of multi-user systems, jump hosts, and endpoints that regularly handle external disk images.
Verify patch deployment through configuration management tooling and confirm reboot completion.

Patch Information

Microsoft has released cumulative updates addressing CVE-2026-50308 across all supported Windows 10, Windows 11, and Windows Server versions listed in the affected products. Refer to the Microsoft Security Update Guide for the specific KB article and package for each build.

Workarounds

Block execution and auto-mounting of untrusted VHD, VHDX, and ISO files via Attack Surface Reduction rules and Group Policy.
Restrict standard users' ability to mount disk images by removing the SeManageVolumePrivilege where operationally feasible.
Filter inbound email attachments and web downloads that contain disk image formats until patches are applied.

bash

# Configuration example: block mounting of disk images via Group Policy registry keys
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsExplorer" /v NoUseStoreOpenWith /t REG_DWORD /d 1 /f
reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\Explorer" /v NoAutoplayfornonVolume /t REG_DWORD /d 1 /f