curl: (35) error:1408F10B:SSL routines:ssl3_get_record:wrong version number

Question

When I try to connect to any server (e.g. google.com) using curl (or libcurl) I get the error message:

curl: (35) error:1408F10B:SSL routines:ssl3_get_record:wrong version number

Verbose output:

$ curl www.google.com --verbose  
* Rebuilt URL to: www.google.com/  
* Uses proxy env variable no_proxy == 'localhost,127.0.0.1,localaddress,.localdomain.com'  
* Uses proxy env variable http_proxy == 'https://proxy.in.tum.de:8080'  
*   Trying 131.159.0.2...  
* TCP_NODELAY set  
* Connected to proxy.in.tum.de (131.159.0.2) port 8080 (#0)  
* successfully set certificate verify locations:  
*   CAfile: /etc/ssl/certs/ca-certificates.crt  
  CApath: none  
* TLSv1.3 (OUT), TLS handshake, Client hello (1):  
* error:1408F10B:SSL routines:ssl3_get_record:wrong version number  
* Closing connection 0  
curl: (35) error:1408F10B:SSL routines:ssl3_get_record:wrong version number'  

For some reason curl seems to use TLSv1.3 even if I force it to use TLSv1.2 with the command --tlsv1.2 (it will still print TLSv1.3 (OUT), ..." I am using the newest version of both Curl and OpenSSL :

$ curl -V  
curl 7.61.0-DEV (x86_64-pc-linux-gnu) libcurl/7.61.0-DEV OpenSSL/1.1.1 zlib/1.2.8  
Release-Date: [unreleased]  
Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp smb smbs smtp smtps telnet tftp  
Features: AsynchDNS IPv6 Largefile NTLM NTLM_WB SSL libz TLS-SRP UnixSockets HTTPS-proxy  

I think this is a problem related to my installation of the programms. Can somebody explain to me what this error message means?

Answer 1

* Uses proxy env variable http_proxy == 'https://proxy.in.tum.de:8080'   
                                         ^^^^^

The https:// is wrong, it should be http://. The proxy itself should be accessed by HTTP and not HTTPS even though the target URL is HTTPS. The proxy will nevertheless properly handle HTTPS connection and keep the end-to-end encryption. See HTTP CONNECT method for details how this is done.