CVE-2026-34345: Microsoft Windows Ancillary Function Driver type confusion privilege escalation

CVE-2026-34345 · Severity: high · CVSS 7 · Published 2026-05-12

A security vulnerability exists in a core Windows networking component responsible for handling socket connections. 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 bypass security restrictions, access sensitive data, or install malicious software.

Technologies: Microsoft Windows 11, Microsoft Windows Ancillary Function Driver for WinSock, Microsoft Windows 10, Microsoft Windows Server 2016, Microsoft Windows Server 2019. Vendors: Microsoft.

Quick answers

Is CVE-2026-34345 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-34345 being exploited in the wild.
How severe is CVE-2026-34345?
High severity, with a CVSS score of 7, published 12 May 2026.
Which products and versions are affected?
Microsoft Windows 11 23H2, 24H2, 25H2, 26H1; Microsoft Windows 10 1607, 1809, 21H2, 22H2.
Is there a fix for CVE-2026-34345?
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-2026-34345 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-34345?
Check whether you run Microsoft Windows 11, Microsoft Windows Ancillary Function Driver for WinSock, Microsoft Windows 10 or one of the others listed 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 type confusion vulnerability exists in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw stems from the driver accessing a resource using an incompatible type, which can be triggered through specific local IOCTL requests. While the advisory also mentions race conditions (CWE-362) and use-after-free (CWE-416) in its change history, the primary root cause is identified as type confusion. An attacker with low-privileged local access can exploit this to execute code in kernel mode, leading to a full local privilege escalation (LPE) to SYSTEM. Microsoft has released security updates to address this issue across supported versions of Windows and Windows Server.

Affected products

  • Microsoft Windows 10 1607, 1809, 21H2, 22H2
  • Microsoft Windows 11 23H2, 24H2, 25H2, 26H1
  • Microsoft Windows Server 2016
  • Microsoft Windows Server 2019

Timeline

  • 2026-05-12: disclosed: Initial disclosure by Microsoft
  • 2026-05-12: advisory: MSRC advisory published
  • 2026-06-01: other: Description updated from race condition to type confusion

References

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