# CVE-2026-20820: Microsoft Windows CLFS Driver heap overflow privilege escalation

Source: https://junglewise.ai/threats/cve-2026-20820-microsoft-windows-clfs-driver-heap-overflow-privilege-escalation  
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-2026-20820 · Severity: high · CVSS 7.8 · Published 2026-01-13

A security vulnerability has been identified in the Windows Common Log File System (CLFS) Driver, a component that manages data logging for the operating system. An attacker who already has basic access to a computer could exploit this flaw to gain full administrative control over the system. This could allow them to view sensitive data, install malicious software, or disrupt business operations.

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-2026-20820 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20820 being exploited in the wild.

**How severe is CVE-2026-20820?** 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-2026-20820?** 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-2026-20820 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-20820?** 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 in the Windows Common Log File System (CLFS) driver. The flaw is triggered when the driver improperly handles objects in memory, allowing a locally authenticated attacker with low privileges to execute code with SYSTEM-level permissions. The attack vector is local, requiring the attacker to run a specially crafted application on the target machine. Microsoft has released security updates to address this issue across various 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-2026-20820](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20820)

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