CVE-2026-62796 Overview
CVE-2026-62796 is an out-of-bounds read vulnerability in the Windows NTFS file system driver. An authorized local attacker can exploit the flaw to read memory beyond intended buffer boundaries and disclose sensitive information. The vulnerability is tracked under [CWE-125] (Out-of-bounds Read) and affects a broad range of Windows client and server operating systems. Microsoft published the advisory on August 11, 2026, and rated the issue medium severity with a CVSS 3.1 base score of 5.5. Exploitation requires local access and low privileges, but no user interaction. Successful exploitation impacts confidentiality only, with no direct effect on integrity or availability.
Critical Impact
An authenticated local attacker can read uninitialized or adjacent NTFS memory contents, potentially exposing sensitive kernel or file system data useful for further privilege escalation chains.
Affected Products
- Microsoft Windows 10 (versions 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (versions 23H2, 24H2, 25H2, 26H1)
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-08-11 - CVE-2026-62796 published to NVD
- 2026-08-13 - Last updated in NVD database
Technical Details for CVE-2026-62796
Vulnerability Analysis
The vulnerability resides in the NTFS driver (ntfs.sys), which handles file system operations on NTFS-formatted volumes. When processing certain file system structures, the driver reads memory outside the bounds of an allocated buffer. This out-of-bounds read exposes adjacent kernel memory contents to the caller. Because NTFS runs in kernel context, the disclosed data can include pointers, tokens, or file system metadata belonging to unrelated processes. The current EPSS estimate places the probability of exploitation in the near term at 0.32%, reflecting a lower likelihood of opportunistic attacks. Nonetheless, information disclosure primitives in kernel components are frequently combined with memory corruption bugs to defeat mitigations such as Kernel Address Space Layout Randomization (KASLR).
Root Cause
The root cause is missing or insufficient bounds validation on a length or offset field within an NTFS on-disk or in-memory structure. When the driver trusts an attacker-influenced size value, it reads past the end of the source buffer. This is a classic [CWE-125] pattern in file system parsers that consume untrusted metadata.
Attack Vector
Exploitation requires local access to the target system with low-privilege user credentials. An attacker triggers the vulnerable code path by presenting a crafted NTFS volume, image, or file system artifact, then invoking an operation that causes the NTFS driver to parse the malformed structure. Mountable virtual hard disks (VHD/VHDX) and removable media are common delivery mechanisms for local NTFS parsing bugs. See the Microsoft CVE-2026-62796 Advisory for full technical guidance.
No public proof-of-concept exploit is currently available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2026-62796
Indicators of Compromise
- Unexpected mounting of VHD, VHDX, or ISO images by non-administrative users on endpoints or servers.
- Repeated NTFS driver errors or ntfs.sys bug checks in the Windows Event Log around user-initiated volume operations.
- Presence of malformed NTFS image files in user-writable directories or temporary paths.
Detection Strategies
- Monitor process activity for local users invoking PowerShell, diskpart, or Mount-DiskImage to attach disk images from untrusted sources.
- Correlate file system driver telemetry with subsequent privilege escalation attempts on the same host within a short time window.
- Alert on kernel-mode read faults originating in ntfs.sys that follow user-initiated mount or file access operations.
Monitoring Recommendations
- Enable Windows Defender Application Control or AppLocker policies that restrict which users can mount disk images.
- Ingest Windows Security, System, and Sysmon logs into a centralized SIEM to correlate mount events with subsequent anomalous behavior.
- Baseline normal NTFS driver behavior per host to detect deviations that may indicate exploitation attempts.
How to Mitigate CVE-2026-62796
Immediate Actions Required
- Apply the Microsoft security updates referenced in the MSRC advisory for CVE-2026-62796 to all affected Windows client and server systems.
- Prioritize patching multi-user systems, terminal servers, and hosts where low-privilege interactive logons are permitted.
- Audit local user privileges and remove unnecessary rights to mount file systems or attach virtual disks.
Patch Information
Microsoft released fixes as part of the August 2026 security update cycle. Administrators should deploy the cumulative update corresponding to each affected Windows build and confirm installation with Get-HotFix or Windows Update reporting in their patch management platform.
Workarounds
- Restrict the ability to mount virtual hard disks and removable media through Group Policy on systems that do not require it.
- Disable auto-mount of removable volumes using mountvol /N where operational requirements permit.
- Limit interactive local logon rights to trusted administrative accounts on sensitive servers until patches are deployed.
# Configuration example: disable automatic mounting of new volumes
mountvol /N
# Verify installed updates on a Windows host
Get-HotFix | Sort-Object -Property InstalledOn -Descending
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
