CVE-2026-68851: Windows NTFS Information Disclosure Flaw

CVE-2026-68851 Overview

CVE-2026-68851 is an information disclosure vulnerability in the Windows NTFS file system driver. The flaw is a buffer over-read [CWE-126] that allows an authenticated local attacker to read memory beyond an allocated buffer. Successful exploitation exposes sensitive kernel or file system memory contents to a low-privileged user on the affected system.

Microsoft published the advisory on September 8, 2026. The vulnerability requires local access and low privileges but no user interaction. It affects confidentiality only, with no impact on integrity or availability of the target system.

Critical Impact
Authenticated local attackers can read out-of-bounds memory from the Windows NTFS driver, potentially exposing sensitive data such as kernel pointers, cryptographic material, or contents of other users' files.

Affected Products

Microsoft Windows (NTFS driver component)
Refer to the Microsoft Security Update CVE-2026-68851 advisory for the definitive list of affected Windows versions and builds
Systems using the NTFS file system on affected Windows releases

Discovery Timeline

2026-09-08 - CVE-2026-68851 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-68851

Vulnerability Analysis

The vulnerability resides in the Windows NTFS driver, which manages the on-disk structures used by the New Technology File System. NTFS parses complex metadata records including Master File Table (MFT) entries, attribute headers, and index structures. When the driver reads past the end of an allocated buffer during this parsing, memory contents from adjacent allocations become accessible to the caller.

Because the NTFS driver operates in kernel mode, over-read data may include kernel heap contents, pool allocations, or cached file data belonging to other security contexts. An authorized local user can trigger the condition by supplying a crafted file system artifact—for example, a malformed volume image, a specially prepared file, or targeted I/O control operations against the NTFS driver.

The issue affects confidentiality only. Attackers cannot modify data or crash the system through this flaw alone. However, disclosed memory contents often accelerate follow-on attacks by revealing kernel address layout, tokens, or handles useful for local privilege escalation chains.

Root Cause

The root cause is classified as CWE-126 (Buffer Over-read). The NTFS driver reads beyond the intended buffer boundary, likely due to a missing or incorrect length validation when processing an attribute or record field. The driver trusts a size or offset value from parsed metadata without confirming it fits within the allocated buffer.

Attack Vector

Exploitation requires local access with low privileges. The attacker interacts with the NTFS driver through standard file system APIs, mounted volumes such as VHD or VHDX images, or crafted files on removable media. No user interaction from another account is required.

Because no verified proof-of-concept code is publicly available, technical details on the specific field or code path are limited. See the Microsoft Security Update CVE-2026-68851 advisory for vendor-supplied technical details.

Detection Methods for CVE-2026-68851

Indicators of Compromise

Unexpected mounting of virtual hard disk files (.vhd, .vhdx, .iso) by non-administrative users
Repeated NTFS driver events or crashes in the System event log correlated with a single low-privileged user session
Creation or access of unusual file system artifacts by processes that do not normally perform disk I/O

Detection Strategies

Monitor process behavior for low-privileged users invoking file system control codes (FSCTL_*) or mounting arbitrary disk images
Alert on unsigned or unusual user-mode binaries issuing raw device I/O against NTFS volumes
Correlate kernel-mode exceptions in ntfs.sys with the user context that triggered the operation

Monitoring Recommendations

Enable Windows audit policies for Removable Storage and File System object access
Ingest Sysmon Event ID 9 (RawAccessRead) and Event ID 11 (FileCreate) into a centralized SIEM for behavioral analysis
Track disk image mount operations through Microsoft-Windows-VHDMP event provider logs

How to Mitigate CVE-2026-68851

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-68851 advisory to all affected Windows systems
Prioritize patching multi-user systems, terminal servers, and shared workstations where local users are least trusted
Audit local user accounts and remove unnecessary interactive logon rights

Patch Information

Microsoft has issued a security update addressing the buffer over-read in the NTFS driver. Administrators should consult the Microsoft Security Update CVE-2026-68851 advisory for the specific KB article and build numbers applicable to each supported Windows version. Deploy through Windows Update, Windows Server Update Services (WSUS), or Microsoft Endpoint Configuration Manager.

Workarounds

Restrict the ability of standard users to mount arbitrary disk images or attach removable NTFS volumes via Group Policy
Disable AutoPlay and AutoRun for removable media to reduce unsolicited NTFS parsing of untrusted volumes
Enforce least-privilege principles and application allowlisting to limit which processes can invoke file system control operations

bash

# Configuration example: disable auto-mounting of new volumes via diskpart
diskpart
automount disable
automount scrub
exit