---
id: CVE-2026-40378
title: >-
  Memory allocation with excessive size value in Windows Local Security
  Authority Subsystem Service (LSASS) allows an unauthorized attacker to deny
  service over a network.
summary: >-
  Memory allocation with excessive size value in Windows Local Security
  Authority Subsystem Service (LSASS) allows an unauthorized attacker to deny
  service over a network.
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-789
vendor: microsoft
product: windows_10_1607
affected:
  - windows_10_1607 < 10.0.14393.9339
  - windows_10_1809 < 10.0.17763.9020
  - windows_10_21h2 < 10.0.19044.7548
  - windows_10_22h2 < 10.0.19045.7548
  - windows_11_23h2 < 10.0.22631.7376
  - windows_11_24h2 < 10.0.26100.8875
  - windows_11_25h2 < 10.0.26200.8875
  - windows_11_26h1 < 10.0.28000.2269
  - windows_server_2012
  - windows_server_2012 = r2
  - windows_server_2016 < 10.0.14393.9339
  - windows_server_2019 < 10.0.17763.9020
  - windows_server_2022 < 10.0.20348.5386
  - windows_server_2025 < 10.0.26100.33158
patched:
  - windows_10_1607 10.0.14393.9339
  - windows_10_1809 10.0.17763.9020
  - windows_10_21h2 10.0.19044.7548
  - windows_10_22h2 10.0.19045.7548
  - windows_11_23h2 10.0.22631.7376
  - windows_11_24h2 10.0.26100.8875
  - windows_11_25h2 10.0.26200.8875
  - windows_11_26h1 10.0.28000.2269
  - windows_server_2016 10.0.14393.9339
  - windows_server_2019 10.0.17763.9020
  - windows_server_2022 10.0.20348.5386
  - windows_server_2025 10.0.26100.33158
published: '2026-07-14'
updated: '2026-07-16'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-40378'
references:
  - url: 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40378'
    label: secure@microsoft.com
tags:
  - nvd
  - cve.org
epss: 0.01174
epssPercentile: 0.66187
ingestedAt: '2026-07-17T13:12:08.602Z'
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-07-14T17:36:13.628087Z'
---

## Overview

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

## Affected

- `windows_10_1607 < 10.0.14393.9339`
- `windows_10_1809 < 10.0.17763.9020`
- `windows_10_21h2 < 10.0.19044.7548`
- `windows_10_22h2 < 10.0.19045.7548`
- `windows_11_23h2 < 10.0.22631.7376`
- `windows_11_24h2 < 10.0.26100.8875`
- `windows_11_25h2 < 10.0.26200.8875`
- `windows_11_26h1 < 10.0.28000.2269`
- `windows_server_2012`
- `windows_server_2012 = r2`
- `windows_server_2016 < 10.0.14393.9339`
- `windows_server_2019 < 10.0.17763.9020`
- `windows_server_2022 < 10.0.20348.5386`
- `windows_server_2025 < 10.0.26100.33158`

## Remediation

Upgrade past the affected range:

- `windows_10_1607 10.0.14393.9339`
- `windows_10_1809 10.0.17763.9020`
- `windows_10_21h2 10.0.19044.7548`
- `windows_10_22h2 10.0.19045.7548`
- `windows_11_23h2 10.0.22631.7376`
- `windows_11_24h2 10.0.26100.8875`
- `windows_11_25h2 10.0.26200.8875`
- `windows_11_26h1 10.0.28000.2269`
- `windows_server_2016 10.0.14393.9339`
- `windows_server_2019 10.0.17763.9020`
- `windows_server_2022 10.0.20348.5386`
- `windows_server_2025 10.0.26100.33158`