TOCTOU Race Condition in Windows WinSock Driver Elevates Privileges

Publication date: 2026-01-13

Last updated on: 2026-01-13

Assigner: Microsoft Corporation

Description

Time-of-check time-of-use (toctou) race condition in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-01-13

Last Modified

2026-01-13

Generated

2026-07-06

AI Q&A

2026-01-14

EPSS Evaluated

2026-07-04

NVD

CVE-2026-20831

Affected Vendors & Products

Vendor	Product	Version / Range
microsoft	windows_ancillary_function_driver_for_winsock	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-367	The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.

Attack-Flow Graph

Executive Summary

This vulnerability is a time-of-check time-of-use (toctou) race condition in the Windows Ancillary Function Driver for WinSock. It allows an authorized attacker to elevate their privileges locally by exploiting the timing issue between checking a condition and using the resource. [1]

Impact Analysis

The vulnerability can allow an authorized attacker to elevate their privileges on the affected Windows system locally. This means the attacker could gain higher-level access than intended, potentially leading to unauthorized actions or control over the system. [1]

Mitigation Strategies

Apply the security updates provided by Microsoft for this vulnerability as soon as possible to mitigate the elevation of privilege risk caused by the toctou race condition in the Windows Ancillary Function Driver for WinSock. [1]

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