Time-of-Check Time-of-Use Vulnerability in Windows HTTP.sys
CVE-2026-21240

7.8HIGH

Key Information:

Vendor

Microsoft
Status
Windows 10 Version 1809
Windows Server 2019
Windows Server 2019 (server Core Installation)
Windows Server 2022
Vendor
CVE Published:
10 February 2026

What is CVE-2026-21240?

A vulnerability exists in Windows HTTP.sys due to a time-of-check time-of-use (TOCTOU) race condition. This flaw can be exploited by an authorized attacker who could execute a local attack to elevate privileges, potentially gaining unauthorized access to sensitive resources. Users are advised to apply the necessary security updates to mitigate this risk.

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Deploy the Patch

Affected Version(s)

Windows 10 Version 1809 32-bit Systems 10.0.17763.0 < 10.0.17763.8389

Windows 10 Version 21H2 32-bit Systems 10.0.19044.0 < 10.0.19044.6937

Windows 10 Version 22H2 x64-based Systems 10.0.19045.0 < 10.0.19045.6937

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE...
vendor-advisorypatch

CVSS V3.1

Score:
7.8
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Local
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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