EUVD-2026-43874
GHSA-x4m3-34g5-88j8
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local low-privileged attacker (AV:L/PR:L) triggers a kernel-mode heap overflow with no user interaction and low complexity, yielding SYSTEM-level full CIA impact.
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 elevate privileges locally.
AnalysisAI
Local privilege escalation in the Microsoft Windows Resilient File System (ReFS) driver allows an authenticated attacker to run code with SYSTEM-level privileges by triggering a heap-based buffer overflow. The flaw (CVSS 7.8) affects a broad range of Windows 10, Windows 11, and Windows Server 2016-2025 builds and carries high confidentiality, integrity, and availability impact. It is a Microsoft-reported issue with a vendor patch available, and there is no public exploit identified at time of analysis.
Technical ContextAI
ReFS is Microsoft's next-generation file system designed for resilience, large-scale data storage, and integrity checking, used on Storage Spaces, Hyper-V volumes, and data-heavy Windows Server workloads. The root cause is CWE-122 (heap-based buffer overflow): the ReFS driver, which runs in kernel mode, mishandles the size of a data structure allocated on the kernel heap, allowing an attacker-controlled operation to write beyond the bounds of the allocation. Because file-system parsing and metadata handling occur in kernel context, corrupting adjacent heap objects can be leveraged to overwrite control data and hijack execution flow at the highest privilege level. The affected CPE set spans desktop SKUs (Windows 10 1607 through Windows 11 26H1) and server SKUs (Windows Server 2016 through Windows Server 2025, including Server Core installations).
RemediationAI
Apply the Microsoft security update for CVE-2026-50407 (Patch available per vendor advisory; consult the MSRC guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50407 for the exact fixed build number for each affected SKU, as the input does not provide a single fix version). Prioritize deployment on servers and workstations that mount or provision ReFS volumes (Storage Spaces, Hyper-V, backup targets). Where immediate patching is not possible, reduce exposure by restricting the ability of low-privileged and untrusted users to attach, mount, or format ReFS volumes and to run arbitrary local code, since exploitation requires local low-privileged access; avoid mounting attacker-supplied or removable ReFS-formatted media, as parsing crafted ReFS metadata is a plausible trigger - the trade-off is operational friction for legitimate removable-storage and virtualization workflows. These are stopgaps only; the vendor patch is the sole complete fix.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Heap Overflow
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External POC / Exploit Code
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