CVE-2026-40398
High
Published: 12 May 2026
Published
12 May 2026
Modified
15 May 2026
KEV Added
—
Patch
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CVSS Score v3.1
7.8
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS Score
0.0002
6.5th percentile
Risk Priority
16
60% EPSS · 20% KEV · 20% CVSS
Summary
CVE-2026-40398 is a high-severity Heap-based Buffer Overflow (CWE-122) vulnerability in Microsoft Windows 10 21H2. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 6.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-29660
Vulnerability details
Heap-based buffer overflow in Windows Remote Desktop allows an authorized attacker to elevate privileges locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
Why these techniques?
Heap buffer overflow in Windows Remote Desktop directly enables local privilege escalation via exploitation (T1068).
Confidence: HIGH · MITRE ATT&CK Enterprise v18.1
CVEs Like This One
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CVE-2026-40377Same product: Microsoft Windows 10 1607
CVE-2026-34343Same product: Microsoft Windows 10 1607
CVE-2026-40403Same product: Microsoft Windows 10 1607
CVE-2026-26176Same product: Microsoft Windows 10 1607
CVE-2026-20922Same product: Microsoft Windows 10 1607
CVE-2026-20820Same product: Microsoft Windows 10 1607
Affected Assets
microsoft
windows 10 1607
≤ 10.0.14393.9140 · ≤ 10.0.14393.9140
microsoft
windows 10 1809
≤ 10.0.17763.8755 · ≤ 10.0.17763.8755
microsoft
windows 10 21h2
≤ 10.0.19044.7291 · ≤ 10.0.19044.7291 · ≤ 10.0.19044.7291
microsoft
windows 10 22h2
≤ 10.0.19045.7291 · ≤ 10.0.19045.7291 · ≤ 10.0.19045.7291
microsoft
windows 11 23h2
≤ 10.0.22631.7079 · ≤ 10.0.22631.7079
microsoft
windows 11 24h2
≤ 10.0.26100.8390 · ≤ 10.0.26100.8390
microsoft
windows 11 25h2
≤ 10.0.26200.8390 · ≤ 10.0.26200.8390
microsoft
windows 11 26h1
≤ 10.0.28000.2113 · ≤ 10.0.28000.2113
microsoft
windows server 2012
all versions, r2
microsoft
windows server 2016
≤ 10.0.14393.9140
+4 more product configuration(s) — see NVD for full list
Mitigating Controls
No mitigating controls mapped yet. The per-CVE control annotator has not reached this CVE.