Improper Verification of Cryptographic Signature in Microsoft Windows and Windows Server - CVE-2026-85818
Published: October 14, 2026
Vulnerability identifier: #VU155166
CSH Severity: High
CVSS v4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-85818
CWE-ID: CWE-347
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to impersonate a trusted client.
The vulnerability exists due to improper verification of cryptographic signatures in Windows Schannel when handling concurrent resumed TLS connections. A remote attacker can win a race condition and substitute a trusted client certificate without proving possession of its private key to impersonate a trusted client.
User interaction is not required.
Affected software
Microsoft Windows
Windows Server
Windows Server
How to mitigate CVE-2026-85818
Install security update from vendor's website.
Microsoft Windows - addressed in versions 11 23H2 10.0.22631.7652, 11 24H2 10.0.26100.9711, 11 25H2 10.0.26200.9711, 11 26H1 10.0.28000.3231
Windows Server - addressed in versions 2022 10.0.20348.5761, 2025 10.0.26100.33650
Windows Server - addressed in versions 2022 10.0.20348.5761, 2025 10.0.26100.33650