PT-2026-88138 · Microsoft · Windows+17

CVE-2026-83991

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Published

2026-09-08

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Updated

2026-09-11

CVSS v3.1

5.5

Medium

VectorAV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
🚨 CVE-2026-83991 Windows Cloud Files
GENERIC WRITE: ACCESS DENIED DeleteFileW: ACCESS DENIED CfCreatePlaceholders with supersede: S OK
same file. same token. leaf DACL said no. sync root path did not care. turns a read-only file into a cloud placeholder.
writeup + PoC by karollooool: https://t.co/xjDoEghdeg
#VulnerabilityResearch #ExploitDev #InfoSec

Fix

Missing Authentication

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dbugs@ptsecurity.com

Weakness Enumeration

CWE-306

Related Identifiers

CVE-2026-83991

Affected Products

Windows
Windows 10 Version 1809
Windows 10 Version 21H2
Windows 10 Version 22H2
Windows 11 Version 23H2
Windows 11 Version 24H2
Windows 11 Version 25H2
Windows 11 Version 26H1
Windows Server 2019
Windows Server 2022
Windows Server 2025
Windows 10 1809
Windows 10 21H2
Windows 10 22H2
Windows 11 23H2
Windows 11 24H2
Windows 11 25H2
Windows 11 26H1