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CVE-2026-20831 Microsoft CVE debrief

CVE-2026-20831 is a time-of-check time-of-use (toctou) race condition vulnerability in the Windows Ancillary Function Driver for WinSock. This vulnerability allows an authorized attacker to elevate privileges locally. The CVE record was published on 2026-01-13T18:16:10.977Z and has not been modified since then. Affected product deployments should be reviewed for potential exposure. The vulnerability has a CVSS score of 7.8 and is classified as HIGH severity. Windows system administrators and security teams should review the official advisory for mitigation guidance.

Vendor
Microsoft
Product
Windows 10 Version 1607
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

Windows system administrators, security teams, and users with local access to Windows systems should be aware of this vulnerability and take steps to patch affected systems. Affected operator teams should review the official advisory for mitigation guidance and prioritize patching for Windows systems. Vulnerability management and security teams should monitor systems for potential exploitation attempts.

Technical summary

CVE-2026-20831 is a time-of-check time-of-use (toctou) race condition vulnerability in the Windows Ancillary Function Driver for WinSock. This vulnerability allows an authorized attacker to elevate privileges locally. The vulnerability has a CVSS score of 7.8 and is classified as HIGH severity. Affected Windows systems should be prioritized for patching. Microsoft has provided a Vendor Advisory for mitigation.

Defensive priority

This vulnerability allows an authorized attacker to elevate privileges locally, which can have a significant impact on the security of a Windows system. Affected users should prioritize patching.

Recommended defensive actions

  • Apply patches from Microsoft as soon as possible
  • Ensure Windows systems are up to date with the latest security updates
  • Monitor systems for potential exploitation attempts
  • Review and update access controls to limit local privilege escalation
  • Review compensating controls for exposed systems while remediation is scheduled and verified

Evidence notes

The CVE-2026-20831 record indicates a time-of-check time-of-use (toctou) race condition in Windows Ancillary Function Driver for WinSock. According to the NVD, this vulnerability has a CVSS score of 7.8 and is classified as HIGH severity. Microsoft has provided a Vendor Advisory for mitigation.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-20831 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-20831

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

  • CVE-2026-20831 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-20831

    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.