CVE-2026-40378

CVE-2026-40378 is a high-severity vulnerability in Microsoft Windows 10 1607 with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-789.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• EPSS exploit prediction: 1% (54th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-789
• Affected product: Microsoft Windows 10 1607
• Published: 2026-07-14
• Last modified: 2026-07-22

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.

Frequently asked questions

What is CVE-2026-40378?

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

How severe is CVE-2026-40378?

CVE-2026-40378 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-40378 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40378?

CVE-2026-40378 primarily affects Microsoft Windows 10 1607. In total, 24 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-40378?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-40378 published?

CVE-2026-40378 was published on 2026-07-14 and last updated on 2026-07-22.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40378

Affected products (24)

• cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:x86:*
• cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_11_25h2:*:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_11_25h2:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_11_26h1:*:*:*:*:*:*:arm64:*
• cpe:2.3:o:microsoft:windows_11_26h1:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:-:*:x64:*
• cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:-:*:x64:*
• cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:x64:*
• cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:x64:*

More vulnerabilities in Microsoft Windows 10 1607

• CVE-2026-57092 — Critical (CVSS 9.9): Use after free in Windows VMSwitch allows an authorized attacker to elevate privileges over a network.
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• CVE-2026-62893 — Critical (CVSS 9.8): Use after free in Windows Deployment Services allows an unauthorized attacker to execute code over a network.
• CVE-2026-62878 — Critical (CVSS 9.8): Stack-based buffer overflow in Windows DNS allows an unauthorized attacker to execute code over a network.
• CVE-2026-56190 — Critical (CVSS 9.8): Use of uninitialized resource in Windows RDP allows an unauthorized attacker to execute code over a network.
• CVE-2026-56188 — Critical (CVSS 9.8): Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Server Network…

All CVEs affecting Microsoft Windows 10 1607 →

Other CWE-789 vulnerabilities

• CVE-2021-34869 — High (CVSS 8.8): This vulnerability allows local attackers to escalate privileges on affected installations of Parallels Desktop…
• CVE-2021-34868 — High (CVSS 8.8): This vulnerability allows local attackers to escalate privileges on affected installations of Parallels Desktop…
• CVE-2026-69219 — High (CVSS 8.7): The RabbitMQ Java client library allows Java and JVM-based applications to connect to and interact with RabbitMQ nodes.…
• CVE-2026-58067 — High (CVSS 8.7): A vulnerability in Veeam Service Provider Console allowing an unauthenticated attacker to exhaust host memory and cause…
• CVE-2026-14682 — High (CVSS 8.7): In Bouncy Castle for Java before 1.85, Possible OOM from unbounded up-front allocation on a definite-length read. This…
• CVE-2026-12852 — High (CVSS 8.7): In Bouncy Castle for Java before 1.85, MLS wire decoder allocates attacker-declared opaque length before bounds check.

Browse all CWE-789 vulnerabilities →