How can i block on Nginx an attack like the code below?

Question

The error shows up in error.log and the server suffers from multiple requests like this one.

FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 127.0.0.1, server: "attacker's ip", request: "GET /random characters.php HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "my server ip"

Kindly asking for help.