EUVD-2026-43899
GHSA-vcff-8fr9-9fhx
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local EoP requiring a low-privileged account (AV:L, PR:L), no user interaction, and a double free yielding SYSTEM code execution gives full C/I/A impact within an unchanged scope.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Double free in Microsoft Brokering File System allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege elevation in the Windows Brokering File System (bfs.sys/brokering component) lets an authenticated low-privileged user corrupt kernel memory via a double free (CWE-415) to gain SYSTEM-level privileges on Windows 11 (24H2, 25H2, 26H1) and Windows Server 2025. A Microsoft-released patch is available. There is no public exploit identified at time of analysis, and the flaw is not listed in CISA KEV; EPSS data was not provided.
Technical ContextAI
The Brokering File System is a Windows kernel-mode component that mediates (brokers) file-system access requests on behalf of sandboxed or lower-integrity processes, enforcing access boundaries between security contexts. The root cause is a double free (CWE-415): the same heap/pool allocation is released twice, which corrupts kernel pool metadata and can be leveraged to overwrite adjacent kernel objects or function pointers, yielding arbitrary kernel-mode code execution or a controlled write primitive. Per the provided CPE data the affected code ships in cpe:2.3:a:microsoft:windows_11_version_24h2, windows_11_version_25h2, windows_11_version_26h1, windows_server_2025, and windows_server_2025 (Server Core installation).
RemediationAI
Apply the Microsoft-released security update for CVE-2026-50361 (Patch available per vendor advisory) via Windows Update or WSUS/SCCM/Autopatch as soon as testing allows; the exact patched build numbers for each affected release are listed in the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50361. No independent standalone workaround is provided in the input data, and because this is a kernel-component double free there is no reliable configuration toggle to disable the Brokering File System; as compensating controls until patching, enforce least privilege to limit the number of interactive/local low-privileged accounts on affected hosts (reducing the pool of would-be local attackers), restrict local and RDP logon rights on Windows Server 2025 systems, and monitor endpoints for unexpected privilege escalation or kernel crashes - with the trade-off that these controls reduce opportunity but do not remove the vulnerable code path.
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Same weakness CWE-415 – Double Free
View allSame technique Information Disclosure
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External POC / Exploit Code
Leaving vuln.today