[3.9] bpo-43882 - Mention urllib.parse changes in Whats new section. (G…

…H-26276)

* [3.9] bpo-43882 - Mention urllib.parse changes in Whats new section.

* Add the missing section.

Doc/whatsnew/3.9.rst

@@ -1560,3 +1560,17 @@ 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`)
+
+Notable changes in Python 3.9.5
+===============================
+
+urllib.parse
+------------
+
+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 in :mod:`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`)
+