Almost every program that we run has access to the environment, so nothing stops them from curling our credentials to some nefarious server.
Why don’t we put credentials in files and then pass them to the programs that need them? Maybe coupled with some mechanism that prevents executables from reading any random file except those approved.
What’s the goal?
There are extra steps you can take to try to improve the security against malware, but using environment variables instead of hard coding isn’t really intended for that, I don’t think.
It’s just to stop accidental leaks with stuff like git and other code sharing.