Newbie alert: Running into sslv3 alert unexpected message

Hi all,

I try to dig into a https connection (of course). I tried to check if everything is set up the right way and used curl to issue a POST request, which was fine. When the system I try to evaluate issues a CONNECT, I get this error displayed in mitmdump: clientconnect CONNECT
<< Cannot establish TLS with client (sni: TlsException(“SSL handshake error: Error([(‘SSL routines’, ‘ssl3_read_bytes’, ‘sslv3 alert unexpected message’)],)”,) clientdisconnect

I was not able to find much about this message. Could you try to point out how to dig into that? I thought maybe the auto detection went wrong and forced mitmdump to use TLS1.2, but that did not help.
I am running this version:

Mitmproxy version: 2.0.2 (release version)
Python version: 3.6.1
Platform: Darwin-16.6.0-x86_64-i386-64bit
SSL version: OpenSSL 1.1.0f 25 May 2017
Mac version: 10.12.5 (’’, ‘’, ‘’) x86_64


The message you are seeing indicates that your client does not trust mitmproxy’s certificate.

Hm… I thought it might be that. But i double-checked and it seems to trust the cert. I used the burp suite now and this works like a charm. Maybe the software uses some dialect mitmproxy has problems with?