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CVE-2026-83991 is an Important-rated missing-authentication vulnerability in the Windows Cloud Files Mini Filter Driver. The driver does not enforce authentication for a critical function, allowing an authorized local attacker to perform tampering against affected functionality or data.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (1 hidden).
This four-file repository contains a standalone Windows local proof of concept for CVE-2026-83991, a Cloud Files minifilter authorization flaw. The primary implementation is main_poc.c; build.bat compiles it with MinGW-w64 GCC or MSVC, while README.md documents the access-control model, reproduction process, and expected results. The C program creates a fresh test directory and file, grants directory-level create/write authority, then applies a protected DACL to the existing file that allows only read access. Using a restricted token, it first establishes that direct GENERIC_WRITE and DeleteFileW operations fail. It then dynamically uses the Cloud Files API to register/connect the parent as a sync root and calls CfCreatePlaceholders with supersede semantics against the existing filename. Successful exploitation is identified by a successful per-entry result, creation USN, reparse-point attribute, and the Cloud Files tag 0x9000001A; it also compares file IDs to determine whether the original object was converted in place. The code contains no remote networking, shell, persistence, or command-execution payload; its capability is local integrity-impacting file-state tampering.
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7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A missing-authentication vulnerability in the Windows Cloud Files Mini Filter Driver that enables an authorized local attacker to tamper with a critical function.
An Important tampering vulnerability in the Windows Cloud Files Mini Filter Driver.
An Important tampering vulnerability in Windows Cloud Files Mini Filter Driver.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.