CVE-2026-66802
High CVSS 8.1Published 2026-08-11 ยท last changed 2026-08-20
The fix
Microsoft fixes this in updatesKB5120238, KB5121000, KB5120242, KB5120229, KB5120233, KB5120228. The fixed build differs per Windows version, so the row that matters is the one matching the machine you are looking at.
| Windows version | Fixed in build | Update | Released |
|---|---|---|---|
| Windows 10 Version 1809 for 32-bit Systems | 10.0.17763.9121 | KB5120238 | 2026-09-20 |
| Windows 10 Version 1809 for x64-based Systems | 10.0.17763.9121 | KB5120238 | 2026-09-20 |
| Windows 11 Version 26H1 for ARM64-based Systems | 10.0.28000.2704 | KB5121000 | 2026-09-20 |
| Windows 11 version 26H1 for x64-based Systems | 10.0.28000.2704 | KB5121000 | 2026-09-20 |
| Windows Server 2019 | 10.0.17763.9121 | KB5120238 | 2026-09-20 |
| Windows Server 2019 (Server Core installation) | 10.0.17763.9121 | KB5120238 | 2026-09-20 |
| Windows Server 2022 | 10.0.20348.5499 | KB5120242, KB5120229 | 2026-09-20 |
| Windows Server 2022 (Server Core installation) | 10.0.20348.5499 | KB5120242, KB5120229 | 2026-09-20 |
| Windows Server 2025 | 10.0.26100.33296 | KB5120233, KB5120228 | 2026-09-20 |
| Windows Server 2025 (Server Core installation) | 10.0.26100.33296 | KB5120233, KB5120228 | 2026-09-20 |
Having the KB is not the same as knowing whether a machine has it. Windows updates supersede each other, so the update you installed often covers a fix that shipped in an earlier one. Paste your build into the patch checker and it walks that chain for you.
What it is
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Device Health Attestation (DHA) allows an unauthorized attacker to execute code over a network.
Sources
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H