CVE-2026-70194: Microsoft Security Advisory CVE-2026-70194 - .NET and Visual Studio Security Feature Bypass Vulnerability

October 13, 2026 (updated October 19, 2026)

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Security. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

.NET 11 post-handshake TLS client authentication can fail to verify the client certificate, allowing mutual-authentication requirements to be bypassed.

References

github.com/advisories/GHSA-fqpq-cx42-9jmm
github.com/dotnet/announcements/issues/464
github.com/dotnet/runtime/issues/135701
github.com/dotnet/runtime/security/advisories/GHSA-fqpq-cx42-9jmm
msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70194
nvd.nist.gov/vuln/detail/CVE-2026-70194

Code Behaviors & Features

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