Attackers make automated scans of servers, collect details about software they are running and then attack software versions that are known to be vulnerable.
A simple way to guard against this when hosting Ghost with Nginx is to quit advertising when you version of Nginx you are running. The steps involved are at this link. By default, Nginx will include an HTTP header with every reply that includes which Nginx version and operating system it is running on.
After the change, it will simply share “nginx”.