The remote certificate is invalid according to the validation procedure
.NET doesn't trust the server's certificate
Seen in .NET (AuthenticationException), HttpClient, SslStream, SqlClient, MailKit
The server certificate failed .NET validation; newer versions append the reason, such as UntrustedRoot or RemoteCertificateNameMismatch.
Common causes
- RemoteCertificateChainErrors or UntrustedRoot: a private or corporate CA, or a missing intermediate.
- RemoteCertificateNameMismatch: the certificate does not cover the hostname used.
- The certificate has expired.
- A Linux container without an up-to-date CA store.
How to fix it
- Read the reason after the message and fix that: chain, name or expiry.
- Install the private CA in the OS trust store (update-ca-certificates on Linux, Trusted Root store on Windows).
- Serve the full chain from the server.
Got a different message? Paste it into the error explainer.
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