I’ve often thought that it is impossible to 100% secure any software that accepts user input.

I wonder if it can be proven?

  def __main__():
    said = input("say something\r\n")
    print(said)

    Equivalent to eval(raw_input(prompt)).

There's no promise that legacy software is safe. There's only a promise it exists, works, gets the job done and releases updates.

... except for software written in Rust, obviously.