EUVD-2026-43808
GHSA-hv8x-xmjg-mmxp
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local vector with low privilege required (attacker needs an existing foothold to drive the ReFS heap path), no user interaction, and driver-context code execution yields full C/I/A impact with unchanged scope.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Heap-based buffer overflow in Windows Resilient File System (ReFS) allows an authorized attacker to execute code locally.
AnalysisAI
Local privilege escalation via arbitrary code execution in Microsoft Windows Resilient File System (ReFS) affects a broad range of Windows 10, Windows 11, and Windows Server (2016-2025) builds. An authorized (low-privileged) attacker who can trigger the vulnerable heap allocation path can corrupt heap memory (CWE-122) to run code in the security context of the ReFS driver, yielding full confidentiality, integrity, and availability impact. No public exploit identified at time of analysis, and the flaw is not on the CISA KEV list.
Technical ContextAI
ReFS is Microsoft's copy-on-write file system, positioned for data-integrity and large-volume workloads (Storage Spaces, Hyper-V, backup targets) as an alternative to NTFS; its parsing and metadata-handling logic runs in kernel-mode driver code. The root cause is CWE-122, a heap-based buffer overflow, meaning the driver writes past the bounds of a dynamically allocated buffer - typically due to an unchecked or miscalculated length when processing file-system structures or I/O requests. Because the CVSS scope is Unchanged (S:U) and the vector is local, exploitation happens within the local system's trust boundary rather than crossing into a separate security authority. The CPE set confirms the affected code ships across Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), and Windows Server 2016/2019 (including Server Core), with tags extending coverage to Server 2022 and Server 2025.
RemediationAI
Apply the Microsoft security update for CVE-2026-49793 (Patch available per vendor advisory) via the standard Windows Update / WSUS / Microsoft Update Catalog channel; consult the MSRC guidance at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-49793 for the exact KB and fixed build numbers for each affected OS version, as those were not enumerated in the input data. Because this is a local elevation-of-privilege issue, patching is the definitive fix; where immediate patching is not possible, reduce exposure by tightening who can obtain the low-privilege foothold and interact with ReFS volumes - restrict interactive and service logon rights on systems using ReFS, limit the placement of untrusted or attacker-controllable files (and the mounting of untrusted removable/VHD ReFS images) on ReFS volumes, and prioritize backup/Hyper-V/Storage Spaces hosts that commonly use ReFS. If ReFS is not required on a given host, migrating those workloads to NTFS removes the attack surface entirely, at the cost of losing ReFS integrity-streams and large-volume features; there is no in-product 'disable ReFS' toggle, so this is the practical compensating control until the update is deployed.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today