What is the CVSS score of CVE-2026-40406?

CVE-2026-40406 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 0.1%.

Which versions of Windows TCP/IP are affected by CVE-2026-40406?

A Windows TCP/IP stack vulnerability (CVE-2026-40406) enables remote, unauthenticated attackers to read sensitive memory contents across all supported Windows versions (Windows 10, 11, and Server…. A patch is available.

How to fix or mitigate CVE-2026-40406?

Within 24 hours, download the vendor patch from Microsoft and begin deployment testing in non-production environments to verify compatibility with Windows 10 (1607 and later), Windows 11, and Windows Server (2012 through 2025). Within 7 days, deploy the patch to all production Windows systems using your standard change management process, prioritizing internet-facing systems and services that handle sensitive data. By 30 days, complete patch rollout across all affected Windows systems organization-wide and verify full deployment via automated compliance scanning.

Windows TCP/IP CVE-2026-40406

EUVD-2026-29666 HIGH

Use After Free (CWE-416)

2026-05-12 microsoft

GHSA-37x6-37vf-qf3r

Denial Of Service Use After Free Memory Corruption Microsoft Windows Server 2012 Windows Server 2016 Windows Server 2019 Windows Server 2022 Windows Server 2025 Windows 10 Version 1607 Windows 10 Version 1809 Windows 10 Version 21H2 Windows 10 Version 22H2 Windows Server 2016 Server Core Installation Windows Server 2019 Server Core Installation Windows 11 Version 22H3 Windows 11 Version 23H2 Windows 11 Version 24H2 Windows 11 Version 25H2 Windows 11 Version 26H1 Windows Server 2022 23H2 Edition Server Core Installation Windows Server 2025 Server Core Installation Windows Server 2012 Server Core Installation Windows Server 2012 R2 Windows Server 2012 R2 Server Core Installation

7.5

CVSS 3.1 · NVD

Temporal: 6.5

Severity by source

NVD PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CIRCL (temporal)

6.5 MEDIUM

cvss

vuln.today AI

7.5 HIGH

Network-reachable, unauthenticated, no user interaction against the core TCP/IP stack with confidentiality-only impact (memory disclosure), so C:H and I:N/A:N.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from NVD.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 22:04 vuln.today

CVE Published

May 12, 2026 - 16:58 nvd

HIGH 7.5

DescriptionCVE.org

Use after free in Windows TCP/IP allows an unauthorized attacker to disclose information over a network.

AnalysisAI

Information disclosure in the Windows TCP/IP networking stack allows a remote, unauthenticated attacker to read sensitive memory contents over the network by triggering a use-after-free condition. All supported Windows client and server releases (Windows 10 1607 through Windows 11 26H1, and Windows Server 2012 through 2025) are affected. Microsoft-reported with no public exploit identified at time of analysis; EPSS is low (0.06%, 19th percentile) and CISA SSVC records exploitation status as none.

Technical ContextAI

The flaw resides in the Windows TCP/IP driver (tcpip.sys), the kernel-mode component that implements IPv4/IPv6, TCP, UDP and related network protocol processing for the entire Windows family. The root cause is CWE-416 (Use After Free): a memory object involved in network packet processing is freed but subsequently referenced, and because attacker-influenced network input reaches this path, the stale memory can be read back. CPE data confirms the affected component spans Windows 10 (1607/1809/21H2/22H2), Windows 11 (22H3/23H2/24H2/25H2/26H1) and Windows Server 2012/2016/2019/2022/2025, indicating a defect in shared core networking code rather than an edition-specific feature.

RemediationAI

Patch available per vendor advisory: apply the Microsoft security update that raises the affected component to at least the fixed build for your release (for example Windows 11 24H2 to 10.0.26100.8457, Windows Server 2025 to 10.0.26100.32860, Windows Server 2019 to 10.0.17763.8755, Windows 10 22H2 to 10.0.19045.7291) via Windows Update or WSUS, per https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40406. Because the vulnerability is reachable over the network in the core TCP/IP stack, there is no clean feature toggle to disable it; as compensating controls until patching, restrict inbound network exposure with host and perimeter firewalls to limit which sources can reach the affected hosts, segment internet-facing and management interfaces, and monitor for anomalous inbound traffic - noting these controls reduce but do not eliminate exposure and may disrupt legitimate connectivity if over-scoped. Additional advisory context is available at https://vuldb.com/vuln/363197 and https://nvd.nist.gov/vuln/detail/CVE-2026-40406.