CVE-2026-83586

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Authentication Bypass in Windows ReFS Deduplication Service

Publication date: 2026-10-13

Last updated on: 2026-10-13

Assigner: Microsoft Corporation

Description

Weak authentication in Windows Resilient File System (ReFS) Deduplication Service allows an authorized attacker to elevate privileges locally.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-13

Last Modified

2026-10-13

Generated

2026-10-19

AI Q&A

2026-10-14

EPSS Evaluated

2026-10-18

NVD

CVE-2026-83586

EUVD

EUVD-2026-99424

Affected Vendors & Products

Vendor	Product	Version / Range
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 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-1390	The product uses an authentication mechanism to restrict access to specific users or identities, but the mechanism does not sufficiently prove that the claimed identity is correct.

Attack-Flow Graph

Executive Summary

This vulnerability involves weak authentication in the Windows Resilient File System (ReFS) Deduplication Service. An authorized attacker can exploit this to elevate their privileges locally on a vulnerable system.

Impact Analysis

An attacker with local access could gain higher privileges, potentially allowing them to install programs, view or delete data, or create new accounts with full user rights.

Compliance Impact

This vulnerability allows local privilege escalation due to weak authentication in the ReFS Deduplication Service. For compliance standards like GDPR or HIPAA, which require strict access controls and data protection, this flaw could enable unauthorized users to gain elevated privileges, potentially leading to unauthorized access to sensitive data. This may result in non-compliance with data protection requirements.

Mitigation Strategies

Apply the latest security updates from Microsoft to patch the weak authentication in the ReFS Deduplication Service. Monitor Microsoft's advisory for updates and ensure all affected Windows versions are updated.

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