CVE-2026-40405Network attack vector

Unauthenticated denial of service via null dereference

Published May 12, 2026 · Updated May 12, 2026

Denial of service in Microsoft Windows TCP/IP allows remote attackers to interrupt affected Windows 11 and Server 2025 systems over a network. The TCP/IP stack dereferences a null pointer while processing attacker-controlled network traffic; Microsoft has not disclosed the specific packet field or code path. No authentication or user interaction is required, and Microsoft has not disclosed whether the interruption causes a hang, crash, or reboot.

CVSS severity7.5
High
EPSS probability1.08%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Microsoft Windows TCP/IP allows remote attackers to interrupt affected Windows 11 and Server 2025 systems over a network. The TCP/IP stack dereferences a null pointer while processing attacker-controlled network traffic; Microsoft has not disclosed the specific packet field or code path. No authentication or user interaction is required, and Microsoft has not disclosed whether the interruption causes a hang, crash, or reboot.

The record

CVE
CVE-2026-40405
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Microsoft
Product
Windows Server 2025 (Server Core installation)
Classifications
CWE-476, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.26100.0 <10.0.26100.32860

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows Server 2025 (Server Core installation)version=10.0.26100.0 <10.0.26100.32860
Microsoft · Windows 11, version 25H2version=10.0.26200.0 <10.0.26200.8457
Microsoft · Windows 11, version 24H2version=10.0.26100.0 <10.0.26100.8457
Microsoft · Windows 11, version 26H1version=10.0.28000.0 <10.0.28000.2113
Microsoft · Windows Server 2025version=10.0.26100.0 <10.0.26100.32860

Published CVSS scores

7.5Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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