CVE-2026-83586

CVE-2026-83586 is an elevation of privilege vulnerability that affects the Windows Resilient File System (ReFS) Deduplication Service. Disclosed by Microsoft as part of its October 2026 Patch Tuesday updates, the flaw is categorized under weak authentication (CWE-1390). This weakness allows an authorized attacker with local access to exploit the deduplication service and elevate their privileges on the affected system. The vulnerability impacts several versions of Microsoft operating systems, including Windows Server 2025 and multiple releases of Windows 11, such as versions 23H2, 24H2, and 25H2. Microsoft has released security patches to address this issue, and administrators are encouraged to apply the updates to prevent potential local privilege escalation.