CVE-2026-40399

Local privilege escalation via TCP/IP race

Published May 12, 2026 · Updated May 12, 2026

Race condition in Windows TCP/IP in affected Microsoft Windows releases allows local users to elevate privileges through local execution. Windows TCP/IP does not properly synchronize concurrent access to a shared resource, allowing a low-privileged process to win a race. A low-privileged local account and code execution are required; successful exploitation raises the attacker's privileges on the host.

CVSS severity7.8
High
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in Windows TCP/IP in affected Microsoft Windows releases allows local users to elevate privileges through local execution. Windows TCP/IP does not properly synchronize concurrent access to a shared resource, allowing a low-privileged process to win a race. A low-privileged local account and code execution are required; successful exploitation raises the attacker's privileges on the host.

The record

CVE
CVE-2026-40399
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Microsoft
Product
Windows Server 2019
Classifications
CWE-121, T1068
Attack vector
local
Privileges
authenticated

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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=10.0.17763.0 <10.0.17763.8755

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.8755
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 Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.9140
Microsoft · Windows 11, version 24H2version=10.0.26100.0 <10.0.26100.8457
Microsoft · Windows 10 Version 21H2version=10.0.19044.0 <10.0.19044.7291
Microsoft · Windows Server 2022, 23H2 Edition (Server Core installation)version=10.0.25398.0 <10.0.25398.2330
Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.9140
Microsoft · Windows 11 Version 22H3version=10.0.22631.0 <10.0.22631.7079
Microsoft · Windows 10 Version 22H2version=10.0.19045.0 <10.0.19045.7291
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.8755
Microsoft · Windows 11, version 26H1version=10.0.28000.0 <10.0.28000.2113
Microsoft · Windows 11 Version 23H2version=10.0.22631.0 <10.0.22631.7079
Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.9140
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.5139
Microsoft · Windows Server 2025version=10.0.26100.0 <10.0.26100.32860
Microsoft · Windows 10 Version 1809version=10.0.17763.0 <10.0.17763.8755

Published CVSS scores

7.8Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
T1068Exploitation for Privilege Escalation

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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