EUVD-2026-29669
GHSA-fccq-6qx5-mcj9
Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Local low-priv attacker (AV:L/PR:L) must win a use-after-free race (AC:H) with no user interaction; successful kernel EoP gives full C/I/A impact.
Primary rating from NVD.
CVSS VectorNVD
Lifecycle Timeline
2DescriptionCVE.org
Use after free in Windows SMB Client allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege escalation in the Microsoft Windows SMB Client (mrxsmb/rdbss) driver lets a low-privileged, authenticated user corrupt kernel memory through a use-after-free (CWE-416) and elevate to SYSTEM. The flaw affects a broad range of Windows client and server builds from Windows Server 2012 R2 through Windows 11 25H2/26H1 and Server 2025. There is no public exploit identified at time of analysis, EPSS is very low (0.04%), and CISA SSVC rates exploitation as 'none' - but technical impact is 'total', so it remains a meaningful patch-Tuesday-class local EoP.
Technical ContextAI
The vulnerability is a use-after-free (CWE-416) in the Windows SMB Client, the kernel-mode component (redirector, typically mrxsmb.sys/rdbss.sys) that handles outbound SMB file-sharing connections. A use-after-free occurs when the driver continues to reference a memory object after it has been freed, allowing an attacker who controls subsequent heap allocations to place attacker-influenced data at the dangling pointer's location and hijack kernel execution or corrupt privileged structures. The CPE set confirms this is Microsoft Windows operating-system code (windows_10 1607/1809/21H2/22H2, windows_11 22H3/23H2/24H2/25H2/26H1, and Windows Server 2012 R2 through 2025), meaning the bug lives in the OS SMB stack rather than any third-party product.
RemediationAI
Apply the Microsoft cumulative security update that raises the OS to at least the fixed build for your version, per Vendor-released patch confirmed in the MSRC advisory: Windows 10 1607/Server 2016 to 10.0.14393.9140, Windows 10 1809/Server 2019 to 10.0.17763.8755, Windows 10 21H2/22H2 to 10.0.19044/19045.7291, Windows 11 22H3/23H2 to 10.0.22631.7079, Windows 11 24H2/25H2 to 10.0.26100.8457/26200.8457, Windows 11 26H1 to 10.0.28000.2113, Server 2012 R2 to 6.3.9600.23181, Server 2022 to 10.0.20348.5139, Server 2022 23H2 core to 10.0.25398.2330, and Server 2025 to 10.0.26100.32860. The update guide is at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40410. Because the flaw is in the SMB client redirector, the exploit path requires a local low-privileged account, so as a compensating control until patching restrict interactive/local logon rights and application execution for standard users to shrink the pool of accounts able to trigger the bug; note this does not remove the vulnerable code and only limits who can reach it. There is no need to expose SMB to the network for this local EoP, so firewall changes are not an effective mitigation here.
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Same weakness CWE-416 – Use After Free
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External POC / Exploit Code
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