Severity by source
AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Local trigger with no privileges or interaction (AV:L/AC:L/PR:N/UI:N); kernel crash affects the whole system (S:C, A:H) with no confidentiality or integrity impact.
Primary rating from NVD.
CVSS VectorNVD
Lifecycle Timeline
2DescriptionCVE.org
Null pointer dereference in Windows TCP/IP allows an unauthorized attacker to deny service locally.
AnalysisAI
Local denial of service in Microsoft Windows TCP/IP networking stack allows an unauthorized local attacker to trigger a null pointer dereference (CWE-476), crashing the system or causing broad service disruption. All supported Windows client and server releases from Windows Server 2012 through Windows 11 25H2/26H1 and Server 2025 are affected. Reported by Microsoft, this is a crash/availability issue only - no code execution or data exposure - with no public exploit identified at time of analysis and a very low (0.05%) EPSS exploitation probability.
Technical ContextAI
The flaw resides in the Windows TCP/IP driver (tcpip.sys), the kernel-mode component implementing the IPv4/IPv6 protocol stack. CWE-476 (NULL Pointer Dereference) indicates that some code path processes network or socket state while an expected pointer is null, causing an unhandled access that faults the kernel. Because the fault occurs in kernel context within the shared networking stack, the impact propagates beyond the triggering process - reflected in the CVSS scope-changed (S:C) rating - typically manifesting as a bugcheck (bluescreen) or loss of network processing. The affected CPE set spans the full Windows 10/11 client family and Server 2012 through 2025, confirming the defect lives in long-lived shared TCP/IP code rather than an edition-specific feature.
RemediationAI
Apply the Microsoft security update for CVE-2026-40401, which is available from the vendor; install the fixed cumulative build for your branch as listed in the MSRC advisory (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40401) - for example Windows 11 24H2 at or above 10.0.26100.8457, Windows Server 2025 at or above 10.0.26100.32860, Windows 10 22H2 at or above 10.0.19045.7291, and Windows Server 2019 at or above 10.0.17763.8755. Patch status: Patch available per vendor advisory. Because exploitation requires local access, the strongest compensating control until patching is to restrict interactive and unprivileged local logon on affected hosts (limit who can run code locally, harden RDP/terminal access), which trades some operational convenience for reduced exposure; there is no configuration toggle to disable the core TCP/IP stack, so patching is the definitive fix. Prioritize multi-user and shared/terminal servers where untrusted local users are most likely to trigger the crash.
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Same weakness CWE-476 – NULL Pointer Dereference
View allSame technique Denial Of Service
View allShare
External POC / Exploit Code
Leaving vuln.today
EUVD-2026-29662
GHSA-8788-537q-vr5m