pythongh-114539: Clarify implicit launching of shells by subprocess (p…

…ythonGH-117996)

(cherry picked from commit a4b44d3)

Co-authored-by: Steve Dower <[email protected]>

Doc/library/subprocess.rst

@@ -754,8 +754,8 @@ Exceptions defined in this module all inherit from :exc:`SubprocessError`.
 Security Considerations
 -----------------------
 
-Unlike some other popen functions, this implementation will never
-implicitly call a system shell.  This means that all characters,
+Unlike some other popen functions, this library will not
+implicitly choose to call a system shell.  This means that all characters,
 including shell metacharacters, can safely be passed to child processes.
 If the shell is invoked explicitly, via ``shell=True``, it is the application's
 responsibility to ensure that all whitespace and metacharacters are
@@ -764,6 +764,14 @@ quoted appropriately to avoid
 vulnerabilities. On :ref:`some platforms <shlex-quote-warning>`, it is possible
 to use :func:`shlex.quote` for this escaping.
 
+On Windows, batch files (:file:`*.bat` or :file:`*.cmd`) may be launched by the
+operating system in a system shell regardless of the arguments passed to this
+library. This could result in arguments being parsed according to shell rules,
+but without any escaping added by Python. If you are intentionally launching a
+batch file with arguments from untrusted sources, consider passing
+``shell=True`` to allow Python to escape special characters. See :gh:`114539`
+for additional discussion.
+
 
 Popen Objects
 -------------