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 10 Version 21h2
Windows 10 Version 22h2
Windows 11 Version 22h3
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.

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 32-bit 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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