CVE-2026-21240

Published: Feb 10, 2026

Modified: May 11, 2026

PUBLISHED

CVSS v3.1

7.8

HIGH

Time-of-check time-of-use (toctou) race condition in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.

Vendor	Product	Versions
Microsoft	Windows 10 Version 1809	affected `10.0.17763.0 - < 10.0.17763.8389`
Microsoft	Windows 10 Version 21H2	affected `10.0.19044.0 - < 10.0.19044.6937`
Microsoft	Windows 10 Version 22H2	affected `10.0.19045.0 - < 10.0.19045.6937`
Microsoft	Windows 11 version 22H3	affected `10.0.22631.0 - < 10.0.22631.6649`
Microsoft	Windows 11 Version 23H2	affected `10.0.22631.0 - < 10.0.22631.6649`
Microsoft	Windows 11 Version 24H2	affected `10.0.26100.0 - < 10.0.26100.7840`
Microsoft	Windows 11 Version 25H2	affected `10.0.26200.0 - < 10.0.26200.7840`
Microsoft	Windows 11 version 26H1	affected `10.0.28000.0 - < 10.0.28000.1575`
Microsoft	Windows 11 Version 26H1	affected `10.0.28000.0 - < 10.0.28000.1575`
Microsoft	Windows Server 2019	affected `10.0.17763.0 - < 10.0.17763.8389`
Microsoft	Windows Server 2019 (Server Core installation)	affected `10.0.17763.0 - < 10.0.17763.8389`
Microsoft	Windows Server 2022	affected `10.0.20348.0 - < 10.0.20348.4773`
Microsoft	Windows Server 2022, 23H2 Edition (Server Core installation)	affected `10.0.25398.0 - < 10.0.25398.2149`
Microsoft	Windows Server 2025	affected `10.0.26100.0 - < 10.0.26100.32370`
Microsoft	Windows Server 2025 (Server Core installation)	affected `10.0.26100.0 - < 10.0.26100.32370`

CVSS v3.1 Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

vendor-advisory

patch

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