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CVE-2026-21240

HighCVSS 7.0/10Last modified Jun 17, 2026

Description

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

Metrics

CVSS 3.1 7.0/10CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness enumeration

Affected software

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

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21240Vendor Advisory

Timeline

Published: Feb 10, 2026
Last modified: Jun 17, 2026
NVD status: Analyzed

Related CVEs from 2026

CVE-2026-212417.0Use after free in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.CVE-2026-212427.0Use after free in Windows Subsystem for Linux allows an authorized attacker to elevate privileges locally.CVE-2026-212437.5Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a netw CVE-2026-212447.3Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to execute code locally.CVE-2026-212457.8Heap-based buffer overflow in Windows Kernel allows an authorized attacker to elevate privileges locally.CVE-2026-212467.8Heap-based buffer overflow in Microsoft Graphics Component allows an authorized attacker to elevate privileges locally.CVE-2026-212477.3Improper input validation in Windows Hyper-V allows an authorized attacker to execute code locally.CVE-2026-212487.3Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to execute code locally.CVE-2026-212493.3External control of file name or path in Windows NTLM allows an unauthorized attacker to perform spoofing locally.CVE-2026-212507.8Untrusted pointer dereference in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.CVE-2026-212517.8Use after free in Windows Cluster Client Failover allows an authorized attacker to elevate privileges locally.CVE-2026-212537.0Use after free in Mailslot File System allows an authorized attacker to elevate privileges locally.

CVE-2026-21240: High severity, CVSS 7.0 | Vulnix