CVE-2026-50402 Overview
CVE-2026-50402 is a local privilege escalation vulnerability in the Windows New Technology File System (NTFS) driver. The flaw stems from an incorrect conversion between numeric types, classified under [CWE-126] (Buffer Over-read). An authenticated local attacker can exploit this weakness to elevate privileges on an affected Windows host. Microsoft published guidance for this issue through the Microsoft Security Response Center (MSRC) Update Guide.
Critical Impact
Successful exploitation grants an authorized local attacker elevated privileges on the target system, compromising confidentiality, integrity, and availability of Windows hosts that rely on NTFS.
Affected Products
- Microsoft Windows (NTFS driver component)
- Refer to the Microsoft CVE-2026-50402 Update Guide for the authoritative list of affected builds
- Specific product SKUs and build numbers were not enumerated in the NVD record at time of publication
Discovery Timeline
- 2026-07-14 - CVE-2026-50402 published to the National Vulnerability Database (NVD)
- 2026-07-15 - Last updated in NVD database
Technical Details for CVE-2026-50402
Vulnerability Analysis
The vulnerability resides in the NTFS driver's handling of numeric type conversions. When NTFS converts values between numeric types of different widths or signedness, the operation produces a truncated or misinterpreted value. This corrupted value is then used in subsequent memory or size calculations within kernel context.
Because NTFS runs as a kernel-mode component, any memory safety error in its code path executes with SYSTEM-level privilege. An attacker who can trigger the flawed conversion, typically by supplying a crafted filesystem structure or invoking a specific file operation, can influence kernel decision logic and escalate from a standard user context to SYSTEM.
Root Cause
The root cause is an incorrect conversion between numeric types, mapped to [CWE-126] Buffer Over-read. Numeric conversion errors of this class commonly occur when a signed integer is cast to an unsigned type, or when a wide integer is narrowed without proper bounds validation. The resulting value bypasses length checks that would otherwise prevent an out-of-bounds read within NTFS kernel buffers.
Attack Vector
The attack vector is local and requires low privileges with no user interaction. An attacker who already has the ability to execute code as a standard user, whether through a compromised account, a foothold from another vulnerability, or interactive access, can trigger the vulnerable NTFS code path. Common triggers for NTFS driver flaws include mounting a crafted virtual hard disk (VHD), interacting with malformed filesystem metadata, or issuing specific file system control (FSCTL) requests.
No public proof-of-concept exploit or in-the-wild exploitation has been reported at time of publication. Detailed exploitation mechanics were not disclosed in the referenced advisory. Consult the Microsoft CVE-2026-50402 Update Guide for vendor-provided technical context.
Detection Methods for CVE-2026-50402
Indicators of Compromise
- Unexpected kernel crashes or bug checks (BSOD) referencing ntfs.sys on hosts where users have recently mounted external or virtual volumes
- Creation of new SYSTEM-level processes spawned from a standard user session without a corresponding administrative action
- Attempted or successful mounting of unusual VHD, VHDX, or ISO files from user-writable directories
Detection Strategies
- Monitor Windows Event Log for kernel-mode faults, driver load anomalies, and unexpected privilege assignments (Event ID 4672) tied to non-administrative accounts
- Alert on process lineage where a standard user process is followed by SYSTEM-integrity process creation without a legitimate elevation path
- Track FSCTL and IOCTL activity against \Device\NTFS originating from low-privileged processes
Monitoring Recommendations
- Enable and forward Sysmon process creation, image load, and driver load events to a centralized analytics platform
- Baseline expected VHD/VHDX mount operations per host and alert on deviations
- Correlate NTFS-related kernel errors with subsequent authentication or privilege change events on the same host
How to Mitigate CVE-2026-50402
Immediate Actions Required
- Apply the Microsoft security update for CVE-2026-50402 as published in the Microsoft CVE-2026-50402 Update Guide
- Prioritize patching on multi-user systems, terminal servers, and virtual desktop infrastructure where local user access is broad
- Audit and restrict which accounts can mount arbitrary VHD or VHDX images on managed endpoints
Patch Information
Microsoft has issued guidance through the MSRC portal. Administrators should install the vendor-supplied cumulative or security-only update that references CVE-2026-50402 for their specific Windows build. Verify patch installation by cross-referencing installed KB identifiers against the MSRC advisory.
Workarounds
- No official vendor workaround was documented in the enriched CVE data; patching is the recommended remediation
- Reduce risk by enforcing the principle of least privilege and removing unnecessary local logon rights
- Restrict the SeManageVolumePrivilege and disk-mount capabilities to administrative accounts only
# Verify Windows update status referencing the MSRC advisory
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
# Audit accounts holding volume management rights
secedit /export /cfg C:\\temp\\secpol.cfg
Select-String -Path C:\\temp\\secpol.cfg -Pattern 'SeManageVolumePrivilege'
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
