Uncontrolled Memory Allocation in Microsoft Windows and Windows Server - CVE-2026-40378

Vulnerability identifier: #VU137959

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-40378

CWE-ID: CWE-789

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to memory allocation with excessive size value in Windows Local Security Authority Subsystem Service (LSASS) when handling network requests. A remote attacker can send a specially crafted request to cause a denial of service.

Microsoft Windows
Windows Server

Install security update from vendor's website.

Microsoft Windows - addressed in versions 10 21H2 10.0.19044.7548, 10 22H2 10.0.19045.7548, 10 1607 10.0.14393.9339, 10 1809 10.0.17763.9020, 11 23H2 10.0.22631.7376, 11 24H2 10.0.26100.8875, 11 25H2 10.0.26200.8875, 11 26H1 10.0.28000.2269, 11 26H1 10.0.28000.2525
Windows Server - addressed in versions 2012 R2 6.3.9600.23291, 2012 6.2.9200.26226, 2016 10.0.14393.9339, 2019 10.0.17763.9020, 2022 10.0.20348.5386, 2025 10.0.26100.33158

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2026-40378

• Multiple vulnerabilities in Microsoft Windows