SB2026011372 - Multiple vulnerabilities in Microsoft Windows Ancillary Function Driver for WinSock

Description

This security bulletin contains information about 3 vulnerabilities.

1) Free of Memory not on the Heap (CVE-ID: CVE-2026-20810)

CWE-ID: CWE-590 - Free of Memory not on the Heap

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear

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

The vulnerability exists due to free of memory not on the heap issue in Windows Ancillary Function Driver for WinSock. A local user can gain elevated privileges on the system.

2) Type Confusion (CVE-ID: CVE-2026-20860)

CWE-ID: CWE-843 - Type confusion

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear

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

The vulnerability exists due to a type confusion error in Windows Ancillary Function Driver for WinSock. A local user can gain elevated privileges on the system.

3) Time-of-check Time-of-use (TOCTOU) Race Condition (CVE-ID: CVE-2026-20831)

CWE-ID: CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear

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

The vulnerability exists due to a time-of-check, time-of-use (TOCTOU) race condition in Windows Ancillary Function Driver for WinSock. A local user can gain elevated privileges on the target system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20810
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20860
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20831