EUVD-2026-44077
GHSA-2926-79wg-c74j
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local authenticated user (AV:L/PR:L) triggers a low-complexity use-after-free to reach SYSTEM, giving full C/I/A impact with no scope change.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Use after free in Microsoft Brokering File System allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege escalation in the Windows Brokering File System affects Windows 11 24H2/25H2/26H1 and Windows Server 2025, where a use-after-free (CWE-416) lets an already-authenticated local user corrupt memory to elevate to higher privileges (typically SYSTEM). Microsoft has released a patch and rates it 7.8 (High). There is no public exploit identified at time of analysis and it is not listed in CISA KEV.
Technical ContextAI
The Brokering File System (bfs) is a Windows broker component that mediates file-system operations across security or integrity boundaries on behalf of less-privileged callers. The root cause is CWE-416, use-after-free: an object is freed while a dangling reference remains reachable, and subsequent operations on that stale pointer allow controlled reuse of the freed allocation. In a brokering component that runs at higher privilege than its callers, reclaiming and grooming the freed object lets an attacker overwrite function pointers or object state to hijack execution or corrupt security-relevant data. The affected CPEs enumerate current-branch client and server builds - Windows 11 version 24H2, 25H2, 26H1, Windows Server 2025 and its Server Core installation - indicating the vulnerable code is in the modern Windows servicing branch rather than legacy releases.
RemediationAI
Apply the Microsoft security update for CVE-2026-50458 - patch available per vendor advisory (Microsoft-reported) at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50458; deploy the corresponding cumulative update / KB for your specific build (Windows 11 24H2, 25H2, 26H1, Windows Server 2025 including Server Core) via Windows Update, WSUS, or Intune as the primary and definitive fix. The provided input does not list an exact fixed build number, so identify the KB for your OS version from the MSRC page before deployment. No official pre-patch workaround is published for this component; because exploitation requires local authenticated access, the practical compensating controls are to reduce local footholds - enforce least privilege so untrusted users cannot run code interactively, restrict who can log on locally and via RDP, and prioritize patching on multi-user, terminal server, or internet-facing hosts where an attacker is most likely to gain an initial low-privilege shell. These controls only shrink the attack surface and do not remediate the underlying use-after-free, so patching remains mandatory.
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Same weakness CWE-416 – Use After Free
View allSame technique Denial Of Service
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External POC / Exploit Code
Leaving vuln.today