CVE-2026-56186
High CVSS 8.1Published 2026-07-14 ยท last changed 2026-07-22
The fix
Microsoft fixes this in updatesKB5099535, KB5099538, KB5099539, KB5101650, KB5101649, KB5099445, KB5099444, KB5099540, KB5099536. 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 1607 for 32-bit Systems | 10.0.14393.9339 | KB5099535 | 2026-09-20 |
| Windows 10 Version 1607 for x64-based Systems | 10.0.14393.9339 | KB5099535 | 2026-09-20 |
| Windows 10 Version 1809 for 32-bit Systems | 10.0.17763.9020 | KB5099538 | 2026-09-20 |
| Windows 10 Version 1809 for x64-based Systems | 10.0.17763.9020 | KB5099538 | 2026-09-20 |
| Windows 10 Version 21H2 for 32-bit Systems | 10.0.19044.7548 | KB5099539 | 2026-09-20 |
| Windows 10 Version 21H2 for ARM64-based Systems | 10.0.19044.7548 | KB5099539 | 2026-09-20 |
| Windows 10 Version 21H2 for x64-based Systems | 10.0.19044.7548 | KB5099539 | 2026-09-20 |
| Windows 10 Version 22H2 for 32-bit Systems | 10.0.19045.7548 | KB5099539 | 2026-09-20 |
| Windows 10 Version 22H2 for ARM64-based Systems | 10.0.19045.7548 | KB5099539 | 2026-09-20 |
| Windows 10 Version 22H2 for x64-based Systems | 10.0.19045.7548 | KB5099539 | 2026-09-20 |
| Windows 11 Version 24H2 for ARM64-based Systems | 10.0.26100.8875 | KB5101650 | 2026-09-20 |
| Windows 11 Version 24H2 for x64-based Systems | 10.0.26100.8875 | KB5101650 | 2026-09-20 |
| Windows 11 Version 25H2 for ARM64-based Systems | 10.0.26200.8875 | KB5101650 | 2026-09-20 |
| Windows 11 Version 25H2 for x64-based Systems | 10.0.26200.8875 | KB5101650 | 2026-09-20 |
| Windows 11 Version 26H1 for ARM64-based Systems | 10.0.28000.2525 | KB5101649 | 2026-09-20 |
| Windows 11 version 26H1 for x64-based Systems | 10.0.28000.2525 | KB5101649 | 2026-09-20 |
| Windows Server 2012 | 6.2.9200.26226 | KB5099445 | 2026-09-20 |
| Windows Server 2012 R2 | 6.3.9600.23291 | KB5099444 | 2026-09-20 |
| Windows Server 2012 R2 (Server Core installation) | 6.3.9600.23291 | KB5099444 | 2026-09-20 |
| Windows Server 2012 (Server Core installation) | 6.2.9200.26226 | KB5099445 | 2026-09-20 |
| Windows Server 2016 | 10.0.14393.9339 | KB5099535 | 2026-09-20 |
| Windows Server 2016 (Server Core installation) | 10.0.14393.9339 | KB5099535 | 2026-09-20 |
| Windows Server 2019 | 10.0.17763.9020 | KB5099538 | 2026-09-20 |
| Windows Server 2019 (Server Core installation) | 10.0.17763.9020 | KB5099538 | 2026-09-20 |
| Windows Server 2022 | 10.0.20348.5386 | KB5099540 | 2026-09-20 |
| Windows Server 2025 | 10.0.26100.33158 | KB5099536 | 2026-09-20 |
| Windows Server 2025 (Server Core installation) | 10.0.26100.33158 | KB5099536 | 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
Out-of-bounds read in Windows Schannel allows an authorized attacker to disclose information over a network.
Sources
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H