EUVD-2026-43979
GHSA-qr4j-65qh-7738
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 kernel UAF with no interaction, yielding SYSTEM control and full C/I/A impact on the same system (S:U).
Primary rating from Vendor (microsoft).
CVSS VectorNVD
Lifecycle Timeline
5DescriptionNVD
Use after free in Windows Kernel allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege escalation in the Windows Kernel affects a broad range of currently supported Windows client and server builds (Windows 10 1809/21H2/22H2, Windows 11 24H2/25H2/26H1, and Windows Server 2019/2022/2025). A use-after-free (CWE-416) in kernel memory lets an already-authenticated local attacker corrupt kernel objects to gain SYSTEM-level privileges. Reported by Microsoft with a patch available; there is no public exploit identified at time of analysis, EPSS is low (0.25%), and SSVC records exploitation status as none.
Technical ContextAI
The flaw resides in the Windows NT kernel (ntoskrnl), the ring-0 core that mediates process/thread scheduling, memory management, object handling, and syscall dispatch for every user-mode process. CWE-416 (Use After Free) means kernel code references a memory object after it has been freed - typically caused by a race, mishandled reference counting, or improper object lifetime management within a kernel dispatch path. An attacker who can reclaim and control the freed allocation (e.g., via pool grooming) can coerce the kernel into using attacker-controlled data as a valid object, yielding arbitrary kernel read/write and ultimately code execution in kernel context. The CPE set confirms the affected surface is the base OS across both 32/64-bit client SKUs and Server Core installations, indicating the vulnerable code path ships in the default kernel of all listed builds.
RemediationAI
Apply the Microsoft cumulative security update that raises the OS to at least the fixed build for your branch: Windows 11 24H2/25H2 to 10.0.26100.8875, Windows 11 26H1 to 10.0.28000.2525, Windows Server 2025 to 10.0.26100.33158, Windows Server 2022 to 10.0.20348.5386, Windows 10 21H2/22H2 to 10.0.19044.7548/10.0.19045.7548, and Windows 10 1809 / Server 2019 to 10.0.17763.9020 (Vendor-released patch confirmed per Microsoft MSRC). The advisory and download links are at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-49167. Because this is a local privilege-escalation with no server-side toggle to disable, there is no direct configuration workaround; compensating controls until patching focus on limiting who can run code locally - enforce least-privilege and remove unnecessary local/interactive logon rights, apply application allowlisting (WDAC/AppLocker) to block unauthorized binaries that would deliver the exploit, and enable attack-surface-reduction and EDR kernel-tamper detection. These controls reduce the pool of attackers who can reach the vulnerable code but do not remove the flaw, so prioritize the update on multi-user hosts (RDS/session hosts, jump boxes) where untrusted users have local execution.
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Same weakness CWE-416 – Use After Free
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External POC / Exploit Code
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