Film Question: Cyber-Attack in 1 line of code?

Hi, I am a filmmaker with only a rudimentary understanding of cybersecurity, and I have an unusual technical question for some research I am doing for a script. I apologise in advance if I sound like a complete newbie...

Is there a line of code (say 8 numerical digits or so) that could, in theory, cause significant damage to a government or military infrastructure?

For example, a line of code or a passkey that could disable a fighter jet, cause a military satellite blackout, shut-down powerplants, etc.

I am working on a project that deals with a cyber vulnerability being leaked in a line of code, but I would like to have something that’s at least semi-realistic and not yet-another ‘Hollywood hacker’ cliche.

What is actually ‘theoretically’ possible in a line of digits?

Open to all suggestions! Thanks