Where to Start?

What I want?

• I wanna install a backdoor/rootkit on a remote server.

What do I have right now:

• this remote server has open ports, I will explain what service is running under this server:

-> It is a node.js application, using a simple code like this: gist.github.com/tedmiston/5935757 (the server code only)

• It is an open source server, as I examined the code, no possibility for buffer overflows (for shellcode execution).
• no other services are running(except from the default open ports)

Question

1. What else can I do to install my backdoor?