CVE-2026-21240 Windows HTTP.sys Elevation of Privilege Vulnerability
A local attacker can exploit a race condition in Windows HTTP.sys to elevate privileges on affected Windows systems.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-21240?
CVE-2026-21240 is a high-severity vulnerability in Microsoft Windows 10 1809, published on 10 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Time-of-check time-of-use (toctou) race condition in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.
Weakness: CWE-367
Which versions are affected by CVE-2026-21240?
It affects 10 products.
Products include Microsoft Windows 10 1809, Microsoft Windows 10 21h2, Microsoft Windows 10 22h2, Microsoft Windows 11 23h2, Microsoft Windows 11 24h2, Microsoft Windows 11 25h2 and 4 more.
How do I fix CVE-2026-21240?
No fix has been published for CVE-2026-21240 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-21240 being exploited?
There is no known exploitation of CVE-2026-21240 in the wild and no public exploit code.
Other vulnerabilities in Microsoft Windows 10 1809
- CVE-2024-29988 Microsoft SmartScreen Prompt Security Feature Bypass
- CVE-2024-21412 Microsoft Windows Internet Shortcut Files Security Feature Bypass
- CVE-2025-62221 Microsoft Windows Use After Free
- CVE-2025-30400 Microsoft Windows DWM Core Library Use-After-Free
- CVE-2024-21338 Microsoft Windows Kernel Exposed IOCTL with Insufficient Access Control
Sources
Also known as GHSA-56fh-gxc8-3p64.