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PatchSiren cyber security CVE debrief

CVE-2026-33099 Microsoft CVE debrief

A vulnerability in the Windows Ancillary Function Driver for WinSock could allow an authorized attacker to elevate privileges locally. Multiple Windows versions are affected, including Windows 10, Windows 11, and Windows Server. This elevation of privilege vulnerability exists due to a use-after-free issue in the Windows Ancillary Function Driver for WinSock. System administrators and security teams should prioritize patching affected versions to prevent potential exploitation. The vulnerability has a high severity score and requires immediate attention.

Vendor
Microsoft
Product
Windows 10 Version 1607
CVSS
HIGH 7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-14
Original CVE updated
2026-10-15
Advisory published
2026-04-14
Advisory updated
2026-10-15

Who should care

System administrators and security teams responsible for Windows systems, especially those with high-risk exposure, should prioritize patching affected versions.

Why it matters

CVE-2026-33099 is a high-severity elevation of privilege vulnerability in the Windows Ancillary Function Driver for WinSock. Affected Windows versions require immediate patching to prevent potential exploitation.

  • Verify and apply patches for affected Windows versions to prevent potential privilege escalation.
  • Assess exposure and prioritize patching for Windows systems with high-risk exposure.
  • Monitor systems for signs of exploitation or anomalous activity.
  • Verify the effectiveness of compensating controls and monitoring.

Technical summary

The vulnerability exists in the Windows Ancillary Function Driver for WinSock, allowing an authorized attacker to elevate privileges locally due to a use-after-free issue. This issue arises when the driver improperly handles memory, leading to potential privilege escalation. Affected Windows versions require immediate patching to prevent potential exploitation. The vulnerability has a high severity score and requires immediate attention.

Defensive priority

Apply patches immediately for affected Windows versions, especially on systems with high-risk exposure.

Recommended defensive actions

  • Apply patches for Windows 10 Version 1607, Windows 10 Version 1809, Windows 10 Version 21H2, Windows 10 Version 22H2, Windows 11 version 23H2, Windows 11 Version 23H2, Windows 11 Version 24H2, Windows 11 Version 25H2,
  • Windows Server 2012, Windows Server 2012 (Server Core installation), Windows Server 2012 R2, Windows Server 2012 R2 (Server Core installation), Windows Server 2016, Windows Server 2016 (Server Core installation), Windows
  • Server 2019, Windows Server 2019 (Server Core installation), Windows Server 2022, Windows Server 2022, 23H2 Edition (Server Core installation)

Evidence notes

The CVE Program and NVD provide official records of the vulnerability. Microsoft has released a patch for the issue. The vulnerability affects multiple Windows versions, including Windows 10, Windows 11, and Windows Server. There is no evidence of exploitation in the wild, but defenders should verify the effectiveness of compensating controls and monitoring. The CVE record was published on 2026-04-14T16:58:39.440Z and has not been modified since then. The official CVE Program record, N

Sources and references

Verified primary and authoritative sources

  • CVE-2026-33099 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-33099

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

  • CVE-2026-33099 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-33099

    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.