From daad2c482c91de32d8305abbccc76a5de8b3a8be Mon Sep 17 00:00:00 2001

From: Steve Dower <steve.dower@microsoft.com>

Date: Thu, 7 Mar 2019 09:08:18 -0800

Subject: [PATCH] bpo-36216: Add check for characters in netloc that normalize

 to separators (GH-12201)

---

 Doc/library/urllib.parse.rst                  | 18 +++++++++++++++

 Lib/test/test_urlparse.py                     | 23 +++++++++++++++++++

 Lib/urllib/parse.py                           | 17 ++++++++++++++

 .../2019-03-06-09-38-40.bpo-36216.6q1m4a.rst  |  3 +++

 4 files changed, 61 insertions(+)

 create mode 100644 Misc/NEWS.d/next/Security/2019-03-06-09-38-40.bpo-36216.6q1m4a.rst

diff --git a/Doc/library/urllib.parse.rst b/Doc/library/urllib.parse.rst

index 0c8f0f607314..b565e1edd321 100644

--- a/Doc/library/urllib.parse.rst

+++ b/Doc/library/urllib.parse.rst

@@ -124,6 +124,11 @@ or on combining URL components into a URL string.

    Unmatched square brackets in the :attr:`netloc` attribute will raise a

    :exc:`ValueError`.

+   Characters in the :attr:`netloc` attribute that decompose under NFKC

+   normalization (as used by the IDNA encoding) into any of ``/``, ``?``,

+   ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is

+   decomposed before parsing, no error will be raised.

+

    .. versionchanged:: 3.2

       Added IPv6 URL parsing capabilities.

@@ -136,6 +141,10 @@ or on combining URL components into a URL string.

       Out-of-range port numbers now raise :exc:`ValueError`, instead of

       returning :const:`None`.

+   .. versionchanged:: 3.7.3

+      Characters that affect netloc parsing under NFKC normalization will

+      now raise :exc:`ValueError`.

+

 .. function:: parse_qs(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None)

@@ -257,10 +266,19 @@ or on combining URL components into a URL string.

    Unmatched square brackets in the :attr:`netloc` attribute will raise a

    :exc:`ValueError`.

+   Characters in the :attr:`netloc` attribute that decompose under NFKC

+   normalization (as used by the IDNA encoding) into any of ``/``, ``?``,

+   ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is

+   decomposed before parsing, no error will be raised.

+

    .. versionchanged:: 3.6

       Out-of-range port numbers now raise :exc:`ValueError`, instead of

       returning :const:`None`.

+   .. versionchanged:: 3.7.3

+      Characters that affect netloc parsing under NFKC normalization will

+      now raise :exc:`ValueError`.

+

 .. function:: urlunsplit(parts)

diff --git a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py

index be50b47603aa..e6638aee2244 100644

--- a/Lib/test/test_urlparse.py

+++ b/Lib/test/test_urlparse.py

@@ -1,3 +1,5 @@

+import sys

+import unicodedata

 import unittest

 import urllib.parse

@@ -984,6 +986,27 @@ def test_all(self):

                 expected.append(name)

         self.assertCountEqual(urllib.parse.__all__, expected)

+    def test_urlsplit_normalization(self):

+        # Certain characters should never occur in the netloc,

+        # including under normalization.

+        # Ensure that ALL of them are detected and cause an error

+        illegal_chars = '/:#?@'

+        hex_chars = {'{:04X}'.format(ord(c)) for c in illegal_chars}

+        denorm_chars = [

+            c for c in map(chr, range(128, sys.maxunicode))

+            if (hex_chars & set(unicodedata.decomposition(c).split()))

+            and c not in illegal_chars

+        ]

+        # Sanity check that we found at least one such character

+        self.assertIn('\u2100', denorm_chars)

+        self.assertIn('\uFF03', denorm_chars)

+

+        for scheme in ["http", "https", "ftp"]:

+            for c in denorm_chars:

+                url = "{}://netloc{}false.netloc/path".format(scheme, c)

+                with self.subTest(url=url, char='{:04X}'.format(ord(c))):

+                    with self.assertRaises(ValueError):

+                        urllib.parse.urlsplit(url)

 class Utility_Tests(unittest.TestCase):

     """Testcase to test the various utility functions in the urllib."""

diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py

index f691ab74f87f..39c5d6a80824 100644

--- a/Lib/urllib/parse.py

+++ b/Lib/urllib/parse.py

@@ -391,6 +391,21 @@ def _splitnetloc(url, start=0):

             delim = min(delim, wdelim)     # use earliest delim position

     return url[start:delim], url[delim:]   # return (domain, rest)

+def _checknetloc(netloc):

+    if not netloc or netloc.isascii():

+        return

+    # looking for characters like \u2100 that expand to 'a/c'

+    # IDNA uses NFKC equivalence, so normalize for this check

+    import unicodedata

+    netloc2 = unicodedata.normalize('NFKC', netloc)

+    if netloc == netloc2:

+        return

+    _, _, netloc = netloc.rpartition('@') # anything to the left of '@' is okay

+    for c in '/?#@:':

+        if c in netloc2:

+            raise ValueError("netloc '" + netloc2 + "' contains invalid " +

+                             "characters under NFKC normalization")

+

 def urlsplit(url, scheme='', allow_fragments=True):

     """Parse a URL into 5 components:

     <scheme>://<netloc>/<path>?<query>#<fragment>

@@ -419,6 +434,7 @@ def urlsplit(url, scheme='', allow_fragments=True):

                 url, fragment = url.split('#', 1)

             if '?' in url:

                 url, query = url.split('?', 1)

+            _checknetloc(netloc)

             v = SplitResult('http', netloc, url, query, fragment)

             _parse_cache[key] = v

             return _coerce_result(v)

@@ -442,6 +458,7 @@ def urlsplit(url, scheme='', allow_fragments=True):

         url, fragment = url.split('#', 1)

     if '?' in url:

         url, query = url.split('?', 1)

+    _checknetloc(netloc)

     v = SplitResult(scheme, netloc, url, query, fragment)

     _parse_cache[key] = v

     return _coerce_result(v)

diff --git a/Misc/NEWS.d/next/Security/2019-03-06-09-38-40.bpo-36216.6q1m4a.rst b/Misc/NEWS.d/next/Security/2019-03-06-09-38-40.bpo-36216.6q1m4a.rst

new file mode 100644

index 000000000000..5546394157f9

--- /dev/null

+++ b/Misc/NEWS.d/next/Security/2019-03-06-09-38-40.bpo-36216.6q1m4a.rst

@@ -0,0 +1,3 @@

+Changes urlsplit() to raise ValueError when the URL contains characters that

+decompose under IDNA encoding (NFKC-normalization) into characters that

+affect how the URL is parsed.