# CVE-2026-20840: Microsoft Windows NTFS heap overflow local code execution

Source: https://junglewise.ai/threats/cve-2026-20840-microsoft-windows-ntfs-heap-overflow-local-code-execution  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-01-13. Updated: 2026-07-30  
License: CC BY 4.0 with a link back

CVE-2026-20840 · Severity: high · CVSS 7.8 · Published 2026-01-13

A security vulnerability has been identified in the Windows NTFS file system, which is responsible for how the operating system stores and retrieves files on hard drives. An attacker who already has basic access to a computer could exploit this flaw to gain full control over the system. This could lead to the theft of sensitive data, the installation of malicious software, or a complete disruption of business operations on the affected machine.

Technologies: [Microsoft Windows 11](https://junglewise.ai/threats/technologies/windows-11), [Microsoft Windows Server 2008 R2](https://junglewise.ai/threats/technologies/windows-server-2008-r2), [Microsoft Windows 10](https://junglewise.ai/threats/technologies/windows-10). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-20840 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20840 being exploited in the wild.

**How severe is CVE-2026-20840?** High severity, with a CVSS score of 7.8, published 13 January 2026.

**Which products and versions are affected?** Microsoft Windows 11 22H3, 23H2, 24H2, 25H2; Microsoft Windows Server 2008 R2 Service Pack 1; Microsoft Windows 10 1607, 1809, 21H2, 22H2.

**Is there a fix for CVE-2026-20840?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-20840 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-20840?** Check whether you run Microsoft Windows 11, Microsoft Windows Server 2008 R2 or Microsoft Windows 10 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap-based buffer overflow vulnerability (CWE-122) exists within the Windows NTFS driver. The flaw is triggered when the system improperly handles memory allocation during file system operations, allowing an attacker to overwrite adjacent memory. To exploit this, an attacker must have local access to the system with low-level user privileges. Successful exploitation allows for local privilege escalation and arbitrary code execution in the context of the kernel or a highly privileged service. Microsoft has released security updates to address this issue across multiple versions of Windows and Windows Server.

## Affected products

- Microsoft Windows 10 1607, 1809, 21H2, 22H2
- Microsoft Windows 11 22H3, 23H2, 24H2, 25H2
- Microsoft Windows Server 2008 R2 Service Pack 1

## Timeline

- 2026-01-13: disclosed
- 2026-01-13: advisory

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20840](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20840)

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