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CVE-2026-20859 Microsoft CVE debrief

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-01-13T18:16:14.810Z and has not been modified since then. The CVE-2026-20859 vulnerability is a use-after-free issue in Windows Kernel-Mode Drivers. This type of vulnerability occurs when a program continues to use a pointer after the memory it points to has been freed or reused. An authorized attacker could exploit this vulnerability to elevate privileges locally. The vulnerability has a CVSS score of 7.8 and is classified as HIGH severity. System administrators and security teams responsible for managing Windows-based systems, particularly those using Windows 11 24H2, Windows 11 25H2, and Windows Server 2025, should be aware of this vulnerability and take steps to mitigate it.

Vendor
Microsoft
Product
Windows 11 Version 24H2
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-01-13
Original CVE updated
2026-07-30
Advisory published
2026-01-13
Advisory updated
2026-07-30

Who should care

System administrators and security teams responsible for managing Windows-based systems, particularly those using Windows 11 24H2, Windows 11 25H2, and Windows Server 2025, should be aware of this vulnerability and take steps to mitigate it.

Technical summary

The CVE-2026-20859 vulnerability is a use-after-free issue in Windows Kernel-Mode Drivers. This type of vulnerability occurs when a program continues to use a pointer after the memory it points to has been freed or reused. An authorized attacker could exploit this vulnerability to elevate privileges locally. The vulnerability has a CVSS score of 7.8 and is classified as HIGH severity.

Defensive priority

This vulnerability allows an authorized attacker to elevate privileges locally, which is a high-risk impact. Affected systems should be prioritized for patching.

Recommended defensive actions

  • Apply patches or updates provided by Microsoft to address the vulnerability in Windows Kernel-Mode Drivers.
  • Ensure that only authorized users have local access to affected systems.
  • Monitor system logs for suspicious activity related to privilege escalation.
  • Consider implementing additional security controls, such as least privilege access and regular vulnerability assessments.

Evidence notes

The CVE-2026-20859 record indicates a use-after-free vulnerability in Windows Kernel-Mode Drivers, which could allow an authorized attacker to elevate privileges locally. The vulnerability has a CVSS score of 7.8 and is classified as HIGH severity. Affected versions include Windows 11 24H2, Windows 11 25H2, and Windows Server 2025.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-20859 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-20859

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-20859 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-20859

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.