SB2026021069 - Multiple vulnerabilities in Microsoft Windows Ancillary Function Driver for WinSock

Description

This security bulletin contains information about 3 secuirty vulnerabilities.

1) Use-after-free (CVE-ID: CVE-2026-21241)

The vulnerability allows a local user to compromise vulnerable system.

The vulnerability exists due to a use-after-free error in Windows Ancillary Function Driver for WinSock. A local user can gain elevated privileges on the target system.

2) Heap-based buffer overflow (CVE-ID: CVE-2026-21236)

The vulnerability allows a local user to escalate privileges on the target system.

The vulnerability exists due to a boundary error in Windows Ancillary Function Driver for WinSock. A local user can pass specially crafted data to the application, trigger a heap-based buffer overflow and gain elevated privileges on the target system.

3) Improper access control (CVE-ID: CVE-2026-21238)

The vulnerability allows a local user to gain unauthorized access to otherwise restricted functionality.

The vulnerability exists due to improper access restrictions in Windows Ancillary Function Driver for WinSock. A local user can bypass implemented security restrictions and gain elevated privileges on the target system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21241
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21236
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21238