CVE-2026-42904: Microsoft Windows 10 21h2

Critical severity, CVSS 9.6. EPSS: 0.5% chance of exploitation in the next 30 days.

Heap-based buffer overflow in Windows TCP/IP allows an unauthorized attacker to elevate privileges over an adjacent network.

Affected products

• Microsoft Windows 10 21h2: before 10.0.19044.7417 (fixed in 10.0.19044.7417)
• Microsoft Windows 10 22h2: before 10.0.19045.7417 (fixed in 10.0.19045.7417)
• Microsoft Windows 11 23h2: before 10.0.22631.7219 (fixed in 10.0.22631.7219)
• Microsoft Windows 11 24h2: before 10.0.26100.8655 (fixed in 10.0.26100.8655)
• Microsoft Windows 11 25h2: before 10.0.26200.8655 (fixed in 10.0.26200.8655)
• Microsoft Windows 11 26h1: before 10.0.28000.2269 (fixed in 10.0.28000.2269)
• Microsoft Windows Server 2022: before 10.0.20348.5256 (fixed in 10.0.20348.5256)
• Microsoft Windows Server 2025: before 10.0.26100.32995 (fixed in 10.0.26100.32995)

Published 2026-06-09. Last modified 2026-07-23.