[3.6] bpo-43882 - Mention urllib.parse changes in Whats New section for 3.6.14 (GH-26268)

Co-authored-by: Gregory P. Smith <[email protected]>

Author: orsenthil

Doc/whatsnew/3.6.rst

@@ -2481,3 +2481,10 @@ IPv4 address sent from the remote server when setting up a passive data
 channel.  We reuse the ftp server IP address instead.  For unusual code
 requiring the old behavior, set a ``trust_server_pasv_ipv4_address``
 attribute on your FTP instance to ``True``.  (See :issue:`43285`)
+
+The presence of newline or tab characters in parts of a URL allows for some
+forms of attacks. Following the WHATWG specification that updates RFC 3986,
+ASCII newline ``\n``, ``\r`` and tab ``\t`` characters are stripped from the
+URL by the parser :func:`urllib.parse` preventing such attacks. The removal
+characters are controlled by a new module level variable
+``urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE``. (See :issue:`43882`)