ssl_reject_handshake breaks other server blocks

[Taco de Wolff]

Thank you Jordan for the response.

Including the SNI information in cURL works, thank you. I wasn't aware this
was so very different from TCP/HTTP2.

The point I was trying to make about the ssl_certificate options to be
mandatory, is that HTTP/2 also requires SSL but recognizes that when
ssl_reject_handshake=on it doesn't need the certificate. For HTTP/3 it
doesn't seem to recognize that it doesn't need the certificate since it
will reject handshakes anyways.

Kind regards,
Taco de Wolff


Op vr 1 mrt 2024 om 05:20 schreef J Carter <jordanc.carter at outlook.com>:

> Hello,
>
> On Wed, 28 Feb 2024 21:45:37 -0300
> Taco de Wolff <tacodewolff at gmail.com> wrote:
>
> > Hi,
> >
> > I've noticed at least in 1.24.0 and 1.25.4 that adding an
> > ssl_reject_handshake to the default server breaks SNI for other
> > servers. Example:
> >
> > ```
> > server {
> >     server_name _;
> >     listen 80 default_server;
> >     listen 443 default_server ssl;
> >     listen 443 default_server quic reuseport;
> >     listen [::]:80 default_server;
> >     listen [::]:443 default_server ssl;
> >     listen [::]:443 default_server quic reuseport;
> >
> >     http2 on;
> >
> >     # SSL
> >     ssl_certificate         /etc/pki/lego/certificates/server.crt;
> >     ssl_certificate_key     /etc/pki/lego/certificates/server.key;
> >     ssl_trusted_certificate /etc/pki/lego/certificates/server.crt;
> >     ssl_reject_handshake on;
> >
> >     return 444;
> > }
> >
> > server {
> >     server_name domain.com;
> >     listen 443 ssl;
> >     listen 443 quic;
> >     listen [::]:443 ssl;
> >     listen [::]:443 quic;
> >
> >     http2 on;
> >
> >     root /srv/www/html;
> >
> >     # SSL
> >     ssl_certificate         /etc/pki/lego/certificates/server.crt;
> >     ssl_certificate_key     /etc/pki/lego/certificates/server.key;
> >     ssl_trusted_certificate /etc/pki/lego/certificates/server.crt;
> >
> >     location / {
> >         try_files /index.html =404;
> >     }
> > }
> > ```
> >
> > There are two remarks for this example:
> > - While enabling HTTP/3 I had to add the ssl_certificate lines to the
> > default server, while using solely HTTP/2 this wasn't necessary. It
> > will throw an error on trying to start Nginx, is that a bug?
>
> TLS is mandatory for HTTP/3 (well, more accurately for QUIC).
>
>
> https://stackoverflow.com/questions/72826710/quic-transfer-protocol-need-not-tls
>
> > - The ssl_reject_handshake in the default server will prevent proper
> > SNI matching for domain.com. If I run `curl https://domain.com/`
> <https://domain.com/> it
> > works fine, but `curl -k -H 'Host: domain.com'
> > https://ipaddress-of-server/` <https://ipaddress-of-server/> does not.
> When I remove
> > ssl_reject_handshake it works as expected
> >
>
> If you curl an IP Address rather than an FQDN, curl will not include
> SNI extension in client hello at all.
>
> ssl_reject_handshake, as the name suggests, rejects TLS handshakes prior
> to completion. Nginx cannot perform secondary search for correct server
> block using host/authority header, as that would require first
> completing handshake, and then parsing host/authority header.
>
> > My intent is to have a default server that responds to non-existing
> > domain names. Preferably it responds with 444, but requests over TLS
> > (such as old domains names with HTST) will throw a security warning
> > that the server's certificates don't match the request's virtual
> > host's domain name (as expected).
> >
>
> return 444; just a special return value that causes nginx to terminate
> connection, nothing get's sent back to the client at all. return
> directives (rewrite module more accurately) runs post TLS handshake
> though. For default server TLS connections with your present
> configuration - it will never get to that point.
>
> Generally ssl_reject_hanshake is preferable for terminating connections
> anyway, as it saves performing heavy TLS handshake.
>
> The return 444 is still relevant for plain text connections that reach
> your default server though, so I'd recommend still keeping it.
>
> > Instead of showing a security warning in the browser I prefer a
> > connection error, which is why I want to employ ssl_reject_handshake.
>
> Your present configuration should work fine then.
>
> > Kind regards,
> > Taco de Wolff
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