gh-102153: Start stripping C0 control and space chars in `urlsplit` (#102508)

`urllib.parse.urlsplit` has already been respecting the WHATWG spec a bit #25595.

This adds more sanitizing to respect the "Remove any leading C0 control or space from input" [rule](https://url.spec.whatwg.org/#url-parsing:~:text=Remove%20any%20leading%20and%20trailing%20C0%20control%20or%20space%20from%20input.) in response to [CVE-2023-24329](https://nvd.nist.gov/vuln/detail/CVE-2023-24329).

---------

Co-authored-by: Gregory P. Smith [Google] <greg@krypto.org>

Doc/library/urllib.parse.rst

@@ -159,6 +159,10 @@ or on combining URL components into a URL string.
       ParseResult(scheme='http', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
                   params='', query='', fragment='')
 
+   .. warning::
+
+      :func:`urlparse` does not perform validation.  See :ref:`URL parsing
+      security <url-parsing-security>` for details.
 
    .. versionchanged:: 3.2
       Added IPv6 URL parsing capabilities.
@@ -324,8 +328,14 @@ or on combining URL components into a URL string.
    ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is
    decomposed before parsing, no error will be raised.
 
-   Following the `WHATWG spec`_ that updates RFC 3986, ASCII newline
-   ``\n``, ``\r`` and tab ``\t`` characters are stripped from the URL.
+   Following some of the `WHATWG spec`_ that updates RFC 3986, leading C0
+   control and space characters are stripped from the URL. ``\n``,
+   ``\r`` and tab ``\t`` characters are removed from the URL at any position.
+
+   .. warning::
+
+      :func:`urlsplit` does not perform validation.  See :ref:`URL parsing
+      security <url-parsing-security>` for details.
 
    .. versionchanged:: 3.6
       Out-of-range port numbers now raise :exc:`ValueError`, instead of
@@ -338,6 +348,9 @@ or on combining URL components into a URL string.
    .. versionchanged:: 3.10
       ASCII newline and tab characters are stripped from the URL.
 
+   .. versionchanged:: 3.12
+      Leading WHATWG C0 control and space characters are stripped from the URL.
+
 .. _WHATWG spec: https://url.spec.whatwg.org/#concept-basic-url-parser
 
 .. function:: urlunsplit(parts)
@@ -414,6 +427,35 @@ or on combining URL components into a URL string.
    or ``scheme://host/path``). If *url* is not a wrapped URL, it is returned
    without changes.
 
+.. _url-parsing-security:
+
+URL parsing security
+--------------------
+
+The :func:`urlsplit` and :func:`urlparse` APIs do not perform **validation** of
+inputs.  They may not raise errors on inputs that other applications consider
+invalid.  They may also succeed on some inputs that might not be considered
+URLs elsewhere.  Their purpose is for practical functionality rather than
+purity.
+
+Instead of raising an exception on unusual input, they may instead return some
+component parts as empty strings. Or components may contain more than perhaps
+they should.
+
+We recommend that users of these APIs where the values may be used anywhere
+with security implications code defensively. Do some verification within your
+code before trusting a returned component part.  Does that ``scheme`` make
+sense?  Is that a sensible ``path``?  Is there anything strange about that
+``hostname``?  etc.
+
+What constitutes a URL is not universally well defined.  Different applications
+have different needs and desired constraints.  For instance the living `WHATWG
+spec`_ describes what user facing web clients such as a web browser require.
+While :rfc:`3986` is more general.  These functions incorporate some aspects of
+both, but cannot be claimed compliant with either.  The APIs and existing user
+code with expectations on specific behaviors predate both standards leading us
+to be very cautious about making API behavior changes.
+
 .. _parsing-ascii-encoded-bytes:
 
 Parsing ASCII Encoded Bytes

Lib/test/test_urlparse.py

@@ -654,6 +654,65 @@ class UrlParseTestCase(unittest.TestCase):
             self.assertEqual(p.scheme, "http")
             self.assertEqual(p.geturl(), "http://www.python.org/javascript:alert('msg')/?query=something#fragment")
 
+    def test_urlsplit_strip_url(self):
+        noise = bytes(range(0, 0x20 + 1))
+        base_url = "http://User:Pass@www.python.org:080/doc/?query=yes#frag"
+
+        url = noise.decode("utf-8") + base_url
+        p = urllib.parse.urlsplit(url)
+        self.assertEqual(p.scheme, "http")
+        self.assertEqual(p.netloc, "User:Pass@www.python.org:080")
+        self.assertEqual(p.path, "/doc/")
+        self.assertEqual(p.query, "query=yes")
+        self.assertEqual(p.fragment, "frag")
+        self.assertEqual(p.username, "User")
+        self.assertEqual(p.password, "Pass")
+        self.assertEqual(p.hostname, "www.python.org")
+        self.assertEqual(p.port, 80)
+        self.assertEqual(p.geturl(), base_url)
+
+        url = noise + base_url.encode("utf-8")
+        p = urllib.parse.urlsplit(url)
+        self.assertEqual(p.scheme, b"http")
+        self.assertEqual(p.netloc, b"User:Pass@www.python.org:080")
+        self.assertEqual(p.path, b"/doc/")
+        self.assertEqual(p.query, b"query=yes")
+        self.assertEqual(p.fragment, b"frag")
+        self.assertEqual(p.username, b"User")
+        self.assertEqual(p.password, b"Pass")
+        self.assertEqual(p.hostname, b"www.python.org")
+        self.assertEqual(p.port, 80)
+        self.assertEqual(p.geturl(), base_url.encode("utf-8"))
+
+        # Test that trailing space is preserved as some applications rely on
+        # this within query strings.
+        query_spaces_url = "https://www.python.org:88/doc/?query=    "
+        p = urllib.parse.urlsplit(noise.decode("utf-8") + query_spaces_url)
+        self.assertEqual(p.scheme, "https")
+        self.assertEqual(p.netloc, "www.python.org:88")
+        self.assertEqual(p.path, "/doc/")
+        self.assertEqual(p.query, "query=    ")
+        self.assertEqual(p.port, 88)
+        self.assertEqual(p.geturl(), query_spaces_url)
+
+        p = urllib.parse.urlsplit("www.pypi.org ")
+        # That "hostname" gets considered a "path" due to the
+        # trailing space and our existing logic...  YUCK...
+        # and re-assembles via geturl aka unurlsplit into the original.
+        # django.core.validators.URLValidator (at least through v3.2) relies on
+        # this, for better or worse, to catch it in a ValidationError via its
+        # regular expressions.
+        # Here we test the basic round trip concept of such a trailing space.
+        self.assertEqual(urllib.parse.urlunsplit(p), "www.pypi.org ")
+
+        # with scheme as cache-key
+        url = "//www.python.org/"
+        scheme = noise.decode("utf-8") + "https" + noise.decode("utf-8")
+        for _ in range(2):
+            p = urllib.parse.urlsplit(url, scheme=scheme)
+            self.assertEqual(p.scheme, "https")
+            self.assertEqual(p.geturl(), "https://www.python.org/")
+
     def test_attributes_bad_port(self):
         """Check handling of invalid ports."""
         for bytes in (False, True):
@@ -661,7 +720,7 @@ class UrlParseTestCase(unittest.TestCase):
                 for port in ("foo", "1.5", "-1", "0x10", "-0", "1_1", " 1", "1 ", "६"):
                     with self.subTest(bytes=bytes, parse=parse, port=port):
                         netloc = "www.example.net:" + port
-                        url = "http://" + netloc
+                        url = "http://" + netloc + "/"
                         if bytes:
                             if netloc.isascii() and port.isascii():
                                 netloc = netloc.encode("ascii")

Lib/urllib/parse.py

@@ -25,6 +25,10 @@ currently not entirely compliant with this RFC due to defacto
 scenarios for parsing, and for backward compatibility purposes, some
 parsing quirks from older RFCs are retained. The testcases in
 test_urlparse.py provides a good indicator of parsing behavior.
+
+The WHATWG URL Parser spec should also be considered.  We are not compliant with
+it either due to existing user code API behavior expectations (Hyrum's Law).
+It serves as a useful guide when making changes.
 """
 
 from collections import namedtuple
@@ -80,6 +84,10 @@ scheme_chars = ('abcdefghijklmnopqrstuvwxyz'
                 '0123456789'
                 '+-.')
 
+# Leading and trailing C0 control and space to be stripped per WHATWG spec.
+# == "".join([chr(i) for i in range(0, 0x20 + 1)])
+_WHATWG_C0_CONTROL_OR_SPACE = '\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f '
+
 # Unsafe bytes to be removed per WHATWG spec
 _UNSAFE_URL_BYTES_TO_REMOVE = ['\t', '\r', '\n']
 
@@ -464,6 +472,10 @@ def urlsplit(url, scheme='', allow_fragments=True):
     """
 
     url, scheme, _coerce_result = _coerce_args(url, scheme)
+    # Only lstrip url as some applications rely on preserving trailing space.
+    # (https://url.spec.whatwg.org/#concept-basic-url-parser would strip both)
+    url = url.lstrip(_WHATWG_C0_CONTROL_OR_SPACE)
+    scheme = scheme.strip(_WHATWG_C0_CONTROL_OR_SPACE)
 
     for b in _UNSAFE_URL_BYTES_TO_REMOVE:
         url = url.replace(b, "")

Misc/NEWS.d/next/Security/2023-03-07-20-59-17.gh-issue-102153.14CLSZ.rst

@@ -0,0 +1,3 @@
+:func:`urllib.parse.urlsplit` now strips leading C0 control and space
+characters following the specification for URLs defined by WHATWG in
+response to CVE-2023-24329. Patch by Illia Volochii.