SSL Handshake failed with OpenSSL error - SSL_ERROR_SSL.

The surrounding chain reads "The SSL connection could not be established" → "Authentication failed, see inner exception." → this message → the OpenSSL reason (for example "error:0A000410:SSL routines::sslv3 alert handshake failure" with OpenSSL 3.0, "ssl/tls alert handshake failure" with 3.3+). On Windows (Schannel) and macOS (Apple's TLS stack) .NET reports such failures with platform-specific messages instead.

.NET on Linux (SslStream over OpenSSL) — inner exception carrying the OpenSSL reason

What it means

On Linux, .NET's SslStream runs on the system OpenSSL, and the handshake failed inside OpenSSL with SSL_ERROR_SSL. This line is a container; the next inner exception (Interop+Crypto+OpenSslCryptographicException) carries the actual OpenSSL reason, such as an alert from the server or a refused protocol version.

Why it happens

• No common cipher suite or protocol version

  common

  Legacy servers with RSA key exchange, 3DES or TLS 1.0/1.1 only; the OpenSSL reason shows the alert the server sent.

• The server required a client certificate

  occasional

  TLS 1.2 mutual-TLS servers answer a missing certificate with a handshake_failure alert.

• The system OpenSSL policy forbids what the server needs

  occasional

  Distribution defaults (security level 2, TLS 1.2 minimum) apply to .NET on Linux too; the same app may work on Windows and fail in a Linux container.

How to fix it

1. 1.

   Read the OpenSSL reason in the innermost exception

   The error:0A… code and text identify the problem; map it as shown.

   Interop+Crypto+OpenSslCryptographicException: error:0A000410:SSL routines::sslv3 alert handshake failure
         -> the server rejected the offered suites/versions (or wants a client certificate)
   error:0A00042E:SSL routines::tlsv1 alert protocol version   -> the server only speaks TLS 1.0/1.1
   error:0A00018A:SSL routines::dh key too small              -> the server uses 1024-bit DH

2. 2.

   Compare server and client capabilities

   Enumerate the server's suites and the local OpenSSL defaults.

   nmap --script ssl-enum-ciphers -p 443 legacy.example.com     # what the server offers
   openssl ciphers -v 'DEFAULT' | head                            # what this system's OpenSSL offers

3. 3.

   Fix the server, not the client policy

   Modernise the server's TLS configuration; relax the client's OpenSSL policy only as a narrow, temporary exception.

   Server side: enable TLS 1.2/1.3 with ECDHE + AES-GCM (or ChaCha20) suites. Lowering the
   system-wide OpenSSL policy (CipherString=DEFAULT@SECLEVEL=1 in openssl.cnf) affects every
   application on the host and should only be a short-lived exception for an isolated legacy peer.

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