CyberSecBulletin
CVE-2026-40378NVD status: Analyzed

Windows 10 Version 1607: Memory Allocation with Excessive Size Value

Published Updated By the CyberSecBulletin desk

CVE-2026-40378 is a high-severity memory allocation with excessive size value vulnerability in Windows 10 Version 1607 from Microsoft, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 10.0.14393.9339 as the first without the flaw, so updating Windows 10 Version 1607 to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 1.17% chance of exploitation within 30 days, higher than 68% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Windows 10 Version 1607 to 10.0.14393.9339 or a later version.
  2. Update Windows 10 Version 1809 to 10.0.17763.9020 or a later version.
  3. Update Windows 10 Version 21H2 to 10.0.19044.7548 or a later version.
  4. Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
  5. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
MicrosoftWindows 10 Version 160710.0.14393.0 up to, but not including, 10.0.14393.933910.0.14393.9339
MicrosoftWindows 10 Version 180910.0.17763.0 up to, but not including, 10.0.17763.902010.0.17763.9020
MicrosoftWindows 10 Version 21H210.0.19044.0 up to, but not including, 10.0.19044.754810.0.19044.7548
MicrosoftWindows 10 Version 22H210.0.19045.0 up to, but not including, 10.0.19045.754810.0.19045.7548
MicrosoftWindows 11 version 23H210.0.22631.0 up to, but not including, 10.0.22631.737610.0.22631.7376
MicrosoftWindows 11 Version 24H210.0.26100.0 up to, but not including, 10.0.26100.887510.0.26100.8875
MicrosoftWindows 11 Version 25H210.0.26200.0 up to, but not including, 10.0.26200.887510.0.26200.8875
MicrosoftWindows 11 version 26H110.0.28000.0 up to, but not including, 10.0.28000.252510.0.28000.2525
MicrosoftWindows Server 20126.2.9200.0 up to, but not including, 6.2.9200.262266.2.9200.26226
MicrosoftWindows Server 2012 (Server Core installation)6.2.9200.0 up to, but not including, 6.2.9200.262266.2.9200.26226
MicrosoftWindows Server 2012 R26.3.9600.0 up to, but not including, 6.3.9600.232916.3.9600.23291
MicrosoftWindows Server 2012 R2 (Server Core installation)6.3.9600.0 up to, but not including, 6.3.9600.232916.3.9600.23291
MicrosoftWindows Server 201610.0.14393.0 up to, but not including, 10.0.14393.933910.0.14393.9339
MicrosoftWindows Server 2016 (Server Core installation)10.0.14393.0 up to, but not including, 10.0.14393.933910.0.14393.9339
MicrosoftWindows Server 201910.0.17763.0 up to, but not including, 10.0.17763.902010.0.17763.9020
MicrosoftWindows Server 2019 (Server Core installation)10.0.17763.0 up to, but not including, 10.0.17763.902010.0.17763.9020
MicrosoftWindows Server 202210.0.20348.0 up to, but not including, 10.0.20348.538610.0.20348.5386
MicrosoftWindows Server 202510.0.26100.0 up to, but not including, 10.0.26100.3315810.0.26100.33158
MicrosoftWindows Server 2025 (Server Core installation)10.0.26100.0 up to, but not including, 10.0.26100.3315810.0.26100.33158
MicrosoftWindows 10 1607before 10.0.14393.933910.0.14393.9339
MicrosoftWindows 10 1809before 10.0.17763.902010.0.17763.9020
MicrosoftWindows 10 21h2before 10.0.19044.754810.0.19044.7548
MicrosoftWindows 10 22h2before 10.0.19045.754810.0.19045.7548
MicrosoftWindows 11 23h2before 10.0.22631.737610.0.22631.7376
MicrosoftWindows 11 24h2before 10.0.26100.887510.0.26100.8875

Version data comes from the organisation that assigned the CVE; 2 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (microsoft.com).

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Memory Allocation with Excessive Size Value

The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.

How developers prevent this class of flaw

  • Perform adequate input validation against any value that influences the amount of memory that is allocated. Define an appropriate strategy for handling requests that exceed the limit, and consider supporting a configuration option so that the administrator can extend the amount of memory to be used if necessary.
  • Run your program using system-provided resource limits for memory. This might still cause the program to crash or exit, but the impact to the rest of the system will be minimized.

More Memory Allocation with Excessive Size Value vulnerabilities (CWE-789)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Memory Allocation with Excessive Size Value vulnerabilities

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