CVE-2026-50412: Windows 10 1607 Privilege Escalation Flaw

CVE-2026-50412 Overview

CVE-2026-50412 is a stack-based buffer overflow vulnerability in the Windows NTFS file system driver. An authorized local attacker can exploit the flaw to elevate privileges on affected systems. Microsoft disclosed the issue through its Security Update Guide, and it affects a broad range of Windows client and server editions from Windows 10 1607 through Windows 11 26H1 and from Windows Server 2012 through Windows Server 2025. The weakness is classified under CWE-121: Stack-based Buffer Overflow. Successful exploitation grants the attacker high impact to confidentiality, integrity, and availability on the compromised host.

Critical Impact
A low-privileged local user can trigger a stack-based buffer overflow in NTFS to gain elevated privileges, potentially achieving SYSTEM-level code execution on unpatched Windows systems.

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-2026-50412 published to the National Vulnerability Database
2026-07-20 - Last updated in NVD database

Technical Details for CVE-2026-50412

Vulnerability Analysis

The vulnerability resides in the New Technology File System (NTFS) driver bundled with Windows. NTFS runs in kernel mode, so any memory corruption in its code paths directly threatens the security boundary between user mode and kernel mode. A stack-based buffer overflow occurs when the driver writes attacker-controlled data past the bounds of a fixed-size stack buffer. This corruption can overwrite adjacent stack variables, saved return addresses, or structured exception handlers.

Because the attack vector is local and requires low privileges, the flaw is well suited for post-compromise privilege escalation. An adversary with initial foothold as a standard user can chain this issue after code execution obtained through phishing, malicious documents, or supply chain compromise.

Root Cause

The root cause is improper bounds checking [CWE-121] in an NTFS routine that processes file system structures on a stack-allocated buffer. When the input length exceeds the buffer capacity, adjacent stack memory is overwritten. Microsoft has not published specific function names, offsets, or the exact metadata field that triggers the overflow. Refer to the Microsoft Security Update Guide entry for CVE-2026-50412 for authoritative details.

Attack Vector

Exploitation requires local access and low privileges but no user interaction. Attackers typically deliver a crafted NTFS volume, image, or file operation that forces the vulnerable code path to parse malformed structures. Mounting a specially crafted VHD or ISO, or performing a targeted file operation against an attacker-controlled NTFS structure, are common exploitation techniques for NTFS memory corruption issues. Success yields kernel-level code execution and full compromise of the host.

Detection Methods for CVE-2026-50412

Indicators of Compromise

Unexpected mounting of virtual hard disk (.vhd, .vhdx) or ISO files by non-administrative users, especially from temporary or user-writable directories
Bug checks (BSODs) referencing ntfs.sys on hosts that lack the July 2026 security update
New SYSTEM-context processes spawned immediately after a low-privileged user session performs disk-image operations

Detection Strategies

Monitor for calls to Win32_DiskImage WMI class and PowerShell cmdlets such as Mount-DiskImage originating from standard user accounts
Correlate NTFS-related kernel crashes (Event ID 1001 with BugcheckCode referencing NTFS) with subsequent privilege changes on the same host
Baseline legitimate use of disk image mounting in the environment and alert on deviations from that baseline

Monitoring Recommendations

Enable kernel-mode crash dump collection and forward ntfs.sys fault telemetry to a centralized analytics platform
Track token elevation events (Windows Security Event ID 4672) that follow unusual file system activity from standard users
Audit creation and deletion of virtual disk files in user profile paths and Downloads folders

How to Mitigate CVE-2026-50412

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-50412 to all affected Windows client and server systems
Prioritize patching multi-user systems, terminal servers, and jump hosts where local users with limited privileges are common
Restrict the ability of non-administrative users to mount disk images through Group Policy or endpoint controls

Patch Information

Microsoft has released cumulative security updates addressing CVE-2026-50412 for all supported Windows versions listed in the affected products section. Consult the Microsoft Security Update Guide for the specific KB article that maps to each Windows build in your environment. Deploy the update through Windows Update, WSUS, Microsoft Intune, or your preferred patch management platform.

Workarounds

Remove or restrict the SeManageVolumePrivilege and disk image mounting rights for standard users where the patch cannot be applied immediately
Enforce application allowlisting to block execution of unknown binaries that could be used to stage local privilege escalation
Disable the automatic mounting of removable media and virtual disks in high-risk environments until patching is complete

bash

# Example: Block standard users from mounting virtual disks via Group Policy setting
# Computer Configuration > Administrative Templates > System > Removable Storage Access
# Set: "All Removable Storage classes: Deny all access" = Enabled
# And apply the following AppLocker rule to block disk image mounts from user paths:
New-AppLockerPolicy -RuleType Path -User "Everyone" -Action Deny -Path "%USERPROFILE%\Downloads\*.vhd*"