Looking for a way to keep a heritage Rails 3.2 app running securely without upgrading

For context - I recently heard a podcast with Eileen Uchitelle where she said that Github had gradually upgraded from Rails 3.2 to 5.1 over the course of the past year or so. While they were using 3.2, they had to patch any known security issues themselves as that version had been EOL'd for quite a while now (ie. at the end of 2015 or so).

My question is, does anybody know if Github open sources these patches for Rails 3.2 at all? I'm basically looking for a way keep a heritage Rails 3.2 app running securely.

I am aware that it is an option to buy this service from a company like railslts but I want to keep that as a last resort for now.