Is CVE-2026-40378 in the CISA KEV catalog?

No. CVE-2026-40378 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-40378?

CVE-2026-40378 has a CVSS v3 base score of 7.5 (Important).

What is the EPSS score for CVE-2026-40378?

CVE-2026-40378 has an EPSS score of 0.82% (53th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-40378?

Install KB5099535 for Windows 10 Version 1607. Fixes are available for 20 affected products.

CVE & CISA-KEV Catalog

CVE-2026-40378

HIGH

7.5

CVSS v3

NVD

Description

Memory allocation with excessive size value in Windows Local Security Authority Subsystem Service (LSASS) allows an unauthorized attacker to deny service over a network.

CWE-789

How to fix

Remediation Available

Windows 10 Version 1607Windows

Install:KB5099535Microsoft

Windows 10 Version 1809Windows

Install:KB5099538Microsoft

Windows 10 Version 21H2Windows

Install:KB5099539Microsoft

Windows 10 Version 22H2Windows

Install:KB5099539Microsoft

Windows 11 Version 23H2Windows

Install:KB5099414Microsoft

Windows 11 Version 24H2Windows

Install:KB5101650Microsoft

Windows 11 Version 25H2Windows

Install:KB5101650Microsoft

Windows 11 Version 26H1Windows

Install:KB5095051Microsoft

Windows 11 version 26H1Windows

Install:KB5095051Microsoft

Windows Server 2012Windows

Install:KB5099445Microsoft

Windows Server 2012 (Server Core installation)Windows

Install:KB5099445Microsoft

Windows Server 2012 R2Windows

Install:KB5099444Microsoft

Windows Server 2012 R2 (Server Core installation)Windows

Install:KB5099444Microsoft

Windows Server 2016Windows

Install:KB5099535Microsoft

Windows Server 2016 (Server Core installation)Windows

Install:KB5099535Microsoft

Windows Server 2019Windows

Install:KB5099538Microsoft

Windows Server 2019 (Server Core installation)Windows

Install:KB5099538Microsoft

Windows Server 2022Windows

Install:KB5099540Microsoft

Windows Server 2025Windows

Install:KB5099536Microsoft

Windows Server 2025 (Server Core installation)Windows

Install:KB5099536Microsoft

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C

Exploit Intelligence

0.82%probability of exploitation in 30 days

53rdpercentile

Moderate risk: more likely to be exploited than 53% of all known CVEs.

References

Vendor Advisory1

msrc.microsoft.com

Related Vulnerabilities

Other CWE-789 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2022-30522	High	7.5	90%	-	Fix
CVE-2026-49975	High	7.5	11%	-	Fix
CVE-2025-27533	High	7.5	8.5%	-	Fix
CVE-2017-7651	High	7.5	5.3%	-	Fix
CVE-2021-31811	Medium	5.5	3.4%	-	-
CVE-2021-27906	Medium	5.5	3.3%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-16.