CVE-2026-56175: Windows NTFS Privilege Escalation Flaw

CVE-2026-56175 Overview

CVE-2026-56175 is a heap-based buffer overflow vulnerability in the Windows New Technology File System (NTFS) driver. An authenticated local attacker can exploit the flaw to elevate privileges on the affected system. The weakness is classified under [CWE-122] (Heap-based Buffer Overflow) and carries a CVSS 3.1 base score of 7.8. Successful exploitation grants an attacker high impact to confidentiality, integrity, and availability, typically resulting in SYSTEM-level code execution. Microsoft addressed the issue through the standard security update channel. No public proof-of-concept code is available, and the vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

Critical Impact
Local, authenticated attackers can trigger a heap overflow in the NTFS driver to escalate from a standard user context to SYSTEM, obtaining full control of the host.

Affected Products

Microsoft Windows (NTFS driver component)
Windows client and server editions that ship the affected NTFS driver
Refer to the Microsoft Security Update Guide for the full list of build numbers and KB identifiers

Discovery Timeline

2026-07-14 - CVE-2026-56175 published to the National Vulnerability Database (NVD)
2026-07-15 - NVD record last modified

Technical Details for CVE-2026-56175

Vulnerability Analysis

The vulnerability resides in the NTFS driver (ntfs.sys), which handles on-disk file system structures for Windows. A heap-based buffer overflow occurs when the driver writes past the bounds of a dynamically allocated pool buffer. Because NTFS parsing runs in kernel mode, corrupting adjacent pool memory allows an attacker to influence kernel data structures. An attacker who gains the ability to overwrite kernel objects can pivot to arbitrary code execution at ring 0. The flaw requires local access and low-privileged authentication, but no user interaction is needed to trigger the vulnerable code path.

Root Cause

The root cause is improper validation of size or length parameters during NTFS metadata processing. When the driver allocates a heap buffer sized according to attacker-influenced input, and subsequently copies data without enforcing the original allocation bounds, it writes beyond the buffer. This class of defect is tracked as [CWE-122] Heap-based Buffer Overflow.

Attack Vector

Exploitation requires local access with valid credentials. A common trigger pattern for NTFS heap overflows involves mounting or accessing a crafted volume, such as a malicious VHD or removable disk image, or invoking a file system operation that causes the driver to parse attacker-controlled structures. Successful exploitation upgrades a standard user session to SYSTEM privileges, enabling installation of persistent implants, credential theft, and lateral movement.

No verified public exploit code is currently available. Technical details are described in prose per the referenced Microsoft Security Update Guide entry.

Detection Methods for CVE-2026-56175

Indicators of Compromise

Unexpected mounting of virtual hard disk (.vhd, .vhdx) or ISO files from user-writable locations
System crashes or bug checks referencing ntfs.sys in MEMORY.DMP or Windows Event Log entries with source BugCheck
Creation of new SYSTEM-context processes spawned from unprivileged parent processes shortly after file system operations

Detection Strategies

Monitor kernel pool corruption indicators through Windows Error Reporting and crash telemetry to identify exploitation attempts that fail
Correlate file system driver crashes with subsequent privilege escalation events, such as new services or scheduled tasks created by non-admin users
Apply behavioral analytics that flag suspicious sequences of disk image mounts followed by token manipulation or process injection

Monitoring Recommendations

Enable and forward Sysmon event IDs 1 (process create), 11 (file create), and 13 (registry set) to a central log repository for retrospective hunting
Audit use of Mount-DiskImage, Mount-VHD, and low-level DeviceIoControl calls targeting the NTFS driver by non-administrative accounts
Track kernel-mode bug checks with stop codes commonly associated with pool corruption, including 0x19 (BAD_POOL_HEADER) and 0xC2 (BAD_POOL_CALLER)

How to Mitigate CVE-2026-56175

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-56175 to all affected Windows hosts
Prioritize patching of multi-user systems, terminal servers, and jump hosts where low-privilege accounts are common
Restrict the ability of standard users to mount arbitrary disk images and connect removable media

Patch Information

Microsoft has released a security update addressing CVE-2026-56175. Administrators should consult the Microsoft Security Update Guide entry for the specific KB numbers and cumulative update packages that apply to each Windows build. Deploy the update through Windows Update, Windows Server Update Services (WSUS), Microsoft Intune, or an equivalent enterprise patch management workflow.

Workarounds

Where immediate patching is not feasible, apply Group Policy restrictions that prevent non-administrative users from mounting VHD or ISO files
Enforce least-privilege access so that unauthenticated or guest accounts cannot obtain the local logon rights required for exploitation
Enable Windows Defender Attack Surface Reduction (ASR) rules and kernel-mode code integrity policies to raise the difficulty of post-exploitation activity

bash

# Example: disable automatic mounting of new volumes for standard users (run as admin)
mountvol /N

# Example: query installed updates to confirm patch presence
wmic qfe list brief | findstr /I "KB"