Ssl-default-server-curves completely ignored

Help!
1

Hi there,

I am sure I am doing something horribly wrong, but I just cannot find out what. I am trying to disable X25519MLKEM768 key exchanges for the backend connections to reduce the overhead of the connection. As such I am running with the following configuration on haproxy docker images haproxytech/haproxy:debian-3.4.5 as well as haproxy:3.4.5:

global
    ssl-default-server-curves secp384r1
    ssl-default-server-options ssl-min-ver TLSv1.3 no-tls-tickets
    
defaults
    mode                    http
    log                     global
    option                  httplog
    option                  dontlognull
    timeout client 1s
    timeout connect 1s
    timeout server 1s

frontend main
    bind *:8080
    default_backend             app
    
frontend test
    bind *:4040
    http-request return status 200 content-type text/plain string OK\n

backend app
    default-server ssl verify none no-sni-auto no-check-sni-auto curves secp384r1
    server test1 127.0.0.1:4040

ssl-default-server-curves secp384r1 is used on purpose for demonstration purposes. Now when connecting via HTTP to port 8080 haproxy tries to make a SSL connection to port 4040. It obviously fails because the backend is not SSL aware but the important part is in the “Client Hello” TLS message that haproxy sends:

image
image1450×539 140 KB

As you can see the key_share still uses X25519MLKEM768. No matter what I try, I cannot get haproxy to send a non pqc aware key exchange.

Any ideas what I am doing wrong?

Thanks,
Florian

2

Uff, it seems to work if I put curves … on the server line, but not when used in default-server or the global options. Sounds like a bug?