CyberSecBulletin
CVE-2026-40399NVD status: Modified

Windows 10 Version 1607: Stack-based Buffer Overflow

Published Updated By the CyberSecBulletin desk

CVE-2026-40399 is a high-severity stack-based buffer overflow vulnerability in Windows 10 Version 1607 from Microsoft, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists version 10.0.14393.9140 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 0.33% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Windows 10 Version 1607 to 10.0.14393.9140 or a later version.
  2. Update Windows 10 Version 1809 to 10.0.17763.8755 or a later version.
  3. Update Windows 10 Version 21H2 to 10.0.19044.7291 or a later version.
  4. Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
MicrosoftWindows 10 Version 160710.0.14393.0 up to, but not including, 10.0.14393.914010.0.14393.9140
MicrosoftWindows 10 Version 180910.0.17763.0 up to, but not including, 10.0.17763.875510.0.17763.8755
MicrosoftWindows 10 Version 21H210.0.19044.0 up to, but not including, 10.0.19044.729110.0.19044.7291
MicrosoftWindows 10 Version 22H210.0.19045.0 up to, but not including, 10.0.19045.741710.0.19045.7417
MicrosoftWindows 11 version 23H210.0.22631.0 up to, but not including, 10.0.22631.7079; 10.0.22631.0 up to, but not including, 10.0.22631.721910.0.22631.7079, 10.0.22631.7219
MicrosoftWindows 11 Version 24H210.0.26100.0 up to, but not including, 10.0.26100.845710.0.26100.8457
MicrosoftWindows 11 Version 25H210.0.26200.0 up to, but not including, 10.0.26200.845710.0.26200.8457
MicrosoftWindows 11 version 26H110.0.28000.0 up to, but not including, 10.0.28000.211310.0.28000.2113
MicrosoftWindows Server 201610.0.14393.0 up to, but not including, 10.0.14393.914010.0.14393.9140
MicrosoftWindows Server 2016 (Server Core installation)10.0.14393.0 up to, but not including, 10.0.14393.914010.0.14393.9140
MicrosoftWindows Server 201910.0.17763.0 up to, but not including, 10.0.17763.875510.0.17763.8755
MicrosoftWindows Server 2019 (Server Core installation)10.0.17763.0 up to, but not including, 10.0.17763.875510.0.17763.8755
MicrosoftWindows Server 202210.0.20348.0 up to, but not including, 10.0.20348.513910.0.20348.5139
MicrosoftWindows Server 2022, 23H2 Edition (Server Core installation)10.0.25398.0 up to, but not including, 10.0.25398.233010.0.25398.2330
MicrosoftWindows Server 202510.0.26100.0 up to, but not including, 10.0.26100.3286010.0.26100.32860
MicrosoftWindows Server 2025 (Server Core installation)10.0.26100.0 up to, but not including, 10.0.26100.3286010.0.26100.32860
MicrosoftWindows 10 1607before 10.0.14393.914010.0.14393.9140
MicrosoftWindows 10 1809before 10.0.17763.875510.0.17763.8755
MicrosoftWindows 10 21h2before 10.0.19044.729110.0.19044.7291
MicrosoftWindows 10 22h2before 10.0.19045.729110.0.19045.7291
MicrosoftWindows 11 23h2before 10.0.22631.707910.0.22631.7079
MicrosoftWindows 11 24h2before 10.0.26100.839010.0.26100.8390
MicrosoftWindows 11 25h2before 10.0.26200.839010.0.26200.8390
MicrosoftWindows 11 26h1before 10.0.28000.211310.0.28000.2113
MicrosoftWindows Server 2022 23h2before 10.0.25398.233010.0.25398.2330

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

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

Official description

Concurrent execution using shared resource with improper synchronization ('race condition') in Windows TCP/IP allows an authorized attacker to elevate privileges locally.

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

The underlying weakness: Stack-based Buffer Overflow

The product writes past the end of a buffer that was allocated on the stack.

How developers prevent this class of flaw

  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
  • Use an abstraction library to abstract away risky APIs. Not a complete solution.
  • Implement and perform bounds checking on input.

More Stack-based Buffer Overflow vulnerabilities (CWE-121)

Timeline

  1. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  2. CVE record published.
  3. Record last changed materially (score, affected products, status or references).

References

Recent Stack-based Buffer Overflow vulnerabilities

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