CVE-2026-84009

Undergoing Analysis Undergoing Analysis - In Progress

Windows Projected File System TOCTOU Race Condition

Publication date: 2026-10-13

Last updated on: 2026-10-16

Assigner: Microsoft Corporation

Description

Time-of-check time-of-use (toctou) race condition in Windows Projected File System allows an authorized attacker to perform tampering locally.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-13

Last Modified

2026-10-16

Generated

2026-10-19

AI Q&A

2026-10-14

EPSS Evaluated

2026-10-18

NVD

CVE-2026-84009

EUVD

EUVD-2026-99446

Affected Vendors & Products

Vendor	Product	Version / Range
Microsoft	Windows	10 Version 1809 10.0.17763.0
Microsoft	Windows	10 Version 21H2 10.0.19044.0
Microsoft	Windows	10 Version 22H2 10.0.19045.0
Microsoft	Windows	11 version 23H2 10.0.22631.0
Microsoft	Windows	11 Version 23H2 10.0.22631.0
Microsoft	Windows	11 Version 24H2 10.0.26100.0
Microsoft	Windows	11 Version 25H2 10.0.26200.0
Microsoft	Windows	11 version 26H1 10.0.28000.0
Microsoft	Windows	11 Version 26H2 10.0.26300.0
Microsoft	Windows	Server 2019 10.0.17763.0
Microsoft	Windows	Server 2019 (Server Core installation) 10.0.17763.0
Microsoft	Windows	Server 2022 10.0.20348.0
Microsoft	Windows	Server 2025 10.0.26100.0
Microsoft	Windows	Server 2025 (Server Core installation) 10.0.26100.0

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 is a time-of-check time-of-use (TOCTOU) race condition in the Windows Projected File System. It allows an authorized local attacker to tamper with files or data by exploiting a timing issue between when a file is checked and when it is used.

Impact Analysis

An attacker with local access could modify files or data during the race condition window, potentially leading to unauthorized changes, data corruption, or system instability. This requires the attacker to already have some level of access to the system.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by allowing unauthorized tampering of files through a race condition. Local tampering risks data integrity, which is critical for maintaining compliance with these regulations.

Mitigation Strategies

Apply the latest security updates from Microsoft to patch the Windows Projected File System vulnerability. Monitor Microsoft's security advisories for updates and disable unnecessary services if required.

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