There's no simple workaround for this behavior. All we can reasonably do is document that running a batch script directly has the same security risks as using shell=True. 

CMD doesn't support a file argument. It only supports running a /c or /k command, which can include running multiple commands joined by the &, &&, or || operators. CreateProcess thus executes a .bat or .cmd script by prepending "%ComSpec% /c" to the command line. If %ComSpec% isn't defined, it defaults to "%SystemRoot%\System32\cmd.exe /c".

Environment variables in a command can be escaped in most cases by inserting the "^" escape character after the first "%" character. This disrupts matching the variable name (unless a variable name happens to start with "^"). The escape character itself gets skipped as long as it isn't quoted literally.