Quick answers
- Is CVE-2026-40401 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-40401 being exploited in the wild.
- How severe is CVE-2026-40401?
- High severity, with a CVSS score of 7.1, published 12 May 2026.
- Which products and versions are affected?
- Microsoft Windows 10 1607, 1809, 21H2, 22H2; Microsoft Windows 11 23H2, 24H2, 25H2, 26H1; Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, 2025, 23H2.
- Is there a fix for CVE-2026-40401?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-40401 attacked?
- It is attacked with local access, in an operating system.
- Am I affected by CVE-2026-40401?
- Check whether you run Microsoft Windows. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A NULL pointer dereference vulnerability (CWE-476) exists in the Windows TCP/IP stack. An unauthorized attacker can exploit this flaw locally to trigger a system crash (Denial of Service). The vulnerability is characterized by a CVSS 3.1 score of 7.1, notably featuring a Scope change (S:C), which often indicates the impact extends beyond the immediate vulnerable component to the entire operating system. Microsoft has released security updates to address this issue across supported versions of Windows 10, 11, and Windows Server.
Affected products
- Microsoft Windows 10 1607, 1809, 21H2, 22H2
- Microsoft Windows 11 23H2, 24H2, 25H2, 26H1
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, 2025, 23H2
Timeline
- 2026-05-12: disclosed
- 2026-05-12: advisory: Microsoft published the security update guide.