Vulnerability in Microsoft Windows 10 1809
CVE-2026-21240
Time-of-check time-of-use (toctou) race condition in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.
Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.003 (18.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 18.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.000
Affected products
- Microsoft Windows 10 1809
- Microsoft Windows 10 21h2
- Microsoft Windows 10 22h2
- Microsoft Windows 10 Version 1809 — versions 10.0.17763.0
- Microsoft Windows 10 Version 21h2 — versions 10.0.19044.0
- Microsoft Windows 10 Version 22h2 — versions 10.0.19045.0
- Microsoft Windows 11 23h2
- Microsoft Windows 11 24h2
- Microsoft Windows 11 25h2
- Microsoft Windows 11 Version 22h3 — versions 10.0.22631.0
Weakness classification (CWE)
References
- Windows HTTP.sys Elevation of Privilege Vulnerability (vendor-advisory, patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-21240?
- CVE-2026-21240 is a high-severity vulnerability in Microsoft Windows 10 1809, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 7.8/10. Published 2026-02-10.
- How severe is CVE-2026-21240?
- High severity. CVSS v3 base score is 7.8 out of 10.