CVE-2026-20810: Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-01-13 · updated 2026-07-30
Weakness: CWE-590

Description

Free of memory not on the heap in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

Affected products

Microsoft Windows 10: before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows 10: before 10.0.19044.6809 — fixed in 10.0.19044.6809
Microsoft Windows 10: before 10.0.19045.6809 — fixed in 10.0.19045.6809
Microsoft Windows Server 2019: before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows 10: from 10.0.17763.0 before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows 10: from 10.0.19044.0 before 10.0.19044.6809 — fixed in 10.0.19044.6809
Microsoft Windows 10: from 10.0.19045.0 before 10.0.19045.6809 — fixed in 10.0.19045.6809
Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.8276 — fixed in 10.0.17763.8276

How to fix

Upgrade to a fixed version: Microsoft Windows 10 10.0.17763.8276; Microsoft Windows 10 10.0.19044.6809; Microsoft Windows 10 10.0.19045.6809; Microsoft Windows Server 2019 10.0.17763.8276; Microsoft Windows 10 10.0.17763.8276; Microsoft Windows 10 10.0.19044.6809; Microsoft Windows 10 10.0.19045.6809; Microsoft Windows Server 2019 10.0.17763.8276. Check the vendor advisory for mitigations.

References

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

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