[kevincox]

That isn't the problem. It is completely possible to process untrusted data in a batch script. (Even if it likely isn't the best tool for the job) the problem is that the method of getting that untrusted data to a batch script is incredibly complex and was being done wrong by a number of programming languages.

For example imagine that I have a shell script to write an entry to a guestbook. Maybe I call it from my webapp like this:

    # webapp.py
    subprocess.run(['guestbook', untrusted_msg])

On Linux this is perfectly fine. I can then write my guestbook script like

    #!/bin/bash
    echo "$1" >> guestbook.txt

As far as I am aware there are no security issues here. The user can pass whatever they want as the message and other than some mess in the `guestbook.txt` file they can't cause any harm.

However this doesn't work well on Windows because in order to escape the arguments you need to know how the `guestbook` program parses its arguments. Right now basically all languages assume that the caller will use `CommandLineToArgvW`. However if `guestbook` is a batch file a different parsing mechanism is used and remote code execution can occur before the batch script even starts executing.

Basically in order to properly escape the arguments the caller needs to know what is being called. The current APIs don't have a way to know this so they can't do it right in all cases.