Setting Nginx to catch all unhandled vhosts

Solution 1:

server_name _; and default_server on the listen configuration are what you are looking for.

Example:

server {

   listen 80 default_server;
   server_name _;

   root /var/www/default; (or wherever)    

}

Solution 2:

If you use SSL, then you need some extra plumbing for a default_server - certificate and key (that can be self-signed).

server {
    server_name _;
    listen 80 default_server;
    listen 443 ssl default_server;
    ssl_certificate <path to cert>;
    ssl_certificate_key <path to key>;
    return 404; # or whatever
}

Nginx will try to accept SSL connection on an IP/port-matching default_server. If such server is missing cert/key, nginx will drop the connection. It won't try other servers. So don't forget cert/key.

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Solution 3:

server {
  listen 80 default_server;
  listen 443 ssl default_server;
  listen [::]:80 default_server;
  listen [::]:443 ssl default_server;

  server_name _;
  root /path/to/default;
}

The entries are for port 80 (HTTP), port 443 (HTTPS), port 80 IPv6, and port 443 IPv6, respectively.

You could consider adding log_not_found off; to avoid adding a log entry for the page not being found.