From: Senthil Kumaran <senthil@uthcode.com>
Date: Wed, 24 Feb 2021 20:04:04 -0800
Subject: [3.6] bpo-42967: only use '&' as a query string separator (GH-24297)
  (GH-24532)
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bpo-42967: [security] Address a web cache-poisoning issue reported in
urllib.parse.parse_qsl().

urllib.parse will only us "&" as query string separator by default
instead of both ";" and "&" as allowed in earlier versions. An optional
argument seperator with default value "&" is added to specify the
separator.

Co-authored-by: Éric Araujo <merwok@netwok.org>
Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
Co-authored-by: Adam Goldschmidt <adamgold7@gmail.com>

CVE-2021-23336

Origin: upstream, https://github.com/python/cpython/commit/5c17dfc5d70ce88be99bc5769b91ce79d7a90d61
Bug-cpython: https://bugs.python.org/issue42967
---
 lib-python/3/cgi.py                | 17 ++++++----
 lib-python/3/test/test_cgi.py      | 29 +++++++++++++---
 lib-python/3/test/test_urlparse.py | 68 ++++++++++++++++++++++++++------------
 lib-python/3/urllib/parse.py       | 19 ++++++++---
 4 files changed, 95 insertions(+), 38 deletions(-)

diff --git a/lib-python/3/cgi.py b/lib-python/3/cgi.py
index 56f243e..1483bed 100755
--- a/lib-python/3/cgi.py
+++ b/lib-python/3/cgi.py
@@ -117,7 +117,8 @@ log = initlog           # The current logging function
 # 0 ==> unlimited input
 maxlen = 0
 
-def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
+def parse(fp=None, environ=os.environ, keep_blank_values=0,
+          strict_parsing=0, separator='&'):
     """Parse a query in the environment or from a file (default stdin)
 
         Arguments, all optional:
@@ -136,6 +137,9 @@ def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
         strict_parsing: flag indicating what to do with parsing errors.
             If false (the default), errors are silently ignored.
             If true, errors raise a ValueError exception.
+
+        separator: str. The symbol to use for separating the query arguments.
+            Defaults to &.
     """
     if fp is None:
         fp = sys.stdin
@@ -180,7 +184,7 @@ def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
             qs = ""
         environ['QUERY_STRING'] = qs    # XXX Shouldn't, really
     return urllib.parse.parse_qs(qs, keep_blank_values, strict_parsing,
-                                 encoding=encoding)
+                                 encoding=encoding, separator=separator)
 
 
 # parse query string function called from urlparse,
@@ -405,7 +409,7 @@ class FieldStorage:
     def __init__(self, fp=None, headers=None, outerboundary=b'',
                  environ=os.environ, keep_blank_values=0, strict_parsing=0,
                  limit=None, encoding='utf-8', errors='replace',
-                 max_num_fields=None):
+                 max_num_fields=None, separator='&'):
         """Constructor.  Read multipart/* until last part.
 
         Arguments, all optional:
@@ -453,6 +457,7 @@ class FieldStorage:
         self.keep_blank_values = keep_blank_values
         self.strict_parsing = strict_parsing
         self.max_num_fields = max_num_fields
+        self.separator = separator
         if 'REQUEST_METHOD' in environ:
             method = environ['REQUEST_METHOD'].upper()
         self.qs_on_post = None
@@ -678,7 +683,7 @@ class FieldStorage:
         query = urllib.parse.parse_qsl(
             qs, self.keep_blank_values, self.strict_parsing,
             encoding=self.encoding, errors=self.errors,
-            max_num_fields=self.max_num_fields)
+            max_num_fields=self.max_num_fields, separator=self.separator)
         self.list = [MiniFieldStorage(key, value) for key, value in query]
         self.skip_lines()
 
@@ -694,7 +699,7 @@ class FieldStorage:
             query = urllib.parse.parse_qsl(
                 self.qs_on_post, self.keep_blank_values, self.strict_parsing,
                 encoding=self.encoding, errors=self.errors,
-                max_num_fields=self.max_num_fields)
+                max_num_fields=self.max_num_fields, separator=self.separator)
             self.list.extend(MiniFieldStorage(key, value) for key, value in query)
 
         klass = self.FieldStorageClass or self.__class__
@@ -736,7 +741,7 @@ class FieldStorage:
 
             part = klass(self.fp, headers, ib, environ, keep_blank_values,
                          strict_parsing,self.limit-self.bytes_read,
-                         self.encoding, self.errors, max_num_fields)
+                         self.encoding, self.errors, max_num_fields, self.separator)
 
             if max_num_fields is not None:
                 max_num_fields -= 1
diff --git a/lib-python/3/test/test_cgi.py b/lib-python/3/test/test_cgi.py
index b3e2d4c..b4d5a12 100644
--- a/lib-python/3/test/test_cgi.py
+++ b/lib-python/3/test/test_cgi.py
@@ -55,12 +55,9 @@ parse_strict_test_cases = [
     ("", ValueError("bad query field: ''")),
     ("&", ValueError("bad query field: ''")),
     ("&&", ValueError("bad query field: ''")),
-    (";", ValueError("bad query field: ''")),
-    (";&;", ValueError("bad query field: ''")),
     # Should the next few really be valid?
     ("=", {}),
     ("=&=", {}),
-    ("=;=", {}),
     # This rest seem to make sense
     ("=a", {'': ['a']}),
     ("&=a", ValueError("bad query field: ''")),
@@ -75,8 +72,6 @@ parse_strict_test_cases = [
     ("a=a+b&b=b+c", {'a': ['a b'], 'b': ['b c']}),
     ("a=a+b&a=b+a", {'a': ['a b', 'b a']}),
     ("x=1&y=2.0&z=2-3.%2b0", {'x': ['1'], 'y': ['2.0'], 'z': ['2-3.+0']}),
-    ("x=1;y=2.0&z=2-3.%2b0", {'x': ['1'], 'y': ['2.0'], 'z': ['2-3.+0']}),
-    ("x=1;y=2.0;z=2-3.%2b0", {'x': ['1'], 'y': ['2.0'], 'z': ['2-3.+0']}),
     ("Hbc5161168c542333633315dee1182227:key_store_seqid=400006&cuyer=r&view=bustomer&order_id=0bb2e248638833d48cb7fed300000f1b&expire=964546263&lobale=en-US&kid=130003.300038&ss=env",
      {'Hbc5161168c542333633315dee1182227:key_store_seqid': ['400006'],
       'cuyer': ['r'],
@@ -180,6 +175,30 @@ class CgiTests(unittest.TestCase):
                     else:
                         self.assertEqual(fs.getvalue(key), expect_val[0])
 
+    def test_separator(self):
+        parse_semicolon = [
+            ("x=1;y=2.0", {'x': ['1'], 'y': ['2.0']}),
+            ("x=1;y=2.0;z=2-3.%2b0", {'x': ['1'], 'y': ['2.0'], 'z': ['2-3.+0']}),
+            (";", ValueError("bad query field: ''")),
+            (";;", ValueError("bad query field: ''")),
+            ("=;a", ValueError("bad query field: 'a'")),
+            (";b=a", ValueError("bad query field: ''")),
+            ("b;=a", ValueError("bad query field: 'b'")),
+            ("a=a+b;b=b+c", {'a': ['a b'], 'b': ['b c']}),
+            ("a=a+b;a=b+a", {'a': ['a b', 'b a']}),
+        ]
+        for orig, expect in parse_semicolon:
+            env = {'QUERY_STRING': orig}
+            fs = cgi.FieldStorage(separator=';', environ=env)
+            if isinstance(expect, dict):
+                for key in expect.keys():
+                    expect_val = expect[key]
+                    self.assertIn(key, fs)
+                    if len(expect_val) > 1:
+                        self.assertEqual(fs.getvalue(key), expect_val)
+                    else:
+                        self.assertEqual(fs.getvalue(key), expect_val[0])
+
     def test_log(self):
         cgi.log("Testing")
 
diff --git a/lib-python/3/test/test_urlparse.py b/lib-python/3/test/test_urlparse.py
index 68f633c..e3088b2 100644
--- a/lib-python/3/test/test_urlparse.py
+++ b/lib-python/3/test/test_urlparse.py
@@ -32,16 +32,10 @@ parse_qsl_test_cases = [
     (b"&a=b", [(b'a', b'b')]),
     (b"a=a+b&b=b+c", [(b'a', b'a b'), (b'b', b'b c')]),
     (b"a=1&a=2", [(b'a', b'1'), (b'a', b'2')]),
-    (";", []),
-    (";;", []),
-    (";a=b", [('a', 'b')]),
-    ("a=a+b;b=b+c", [('a', 'a b'), ('b', 'b c')]),
-    ("a=1;a=2", [('a', '1'), ('a', '2')]),
-    (b";", []),
-    (b";;", []),
-    (b";a=b", [(b'a', b'b')]),
-    (b"a=a+b;b=b+c", [(b'a', b'a b'), (b'b', b'b c')]),
-    (b"a=1;a=2", [(b'a', b'1'), (b'a', b'2')]),
+    (";a=b", [(';a', 'b')]),
+    ("a=a+b;b=b+c", [('a', 'a b;b=b c')]),
+    (b";a=b", [(b';a', b'b')]),
+    (b"a=a+b;b=b+c", [(b'a', b'a b;b=b c')]),
 ]
 
 # Each parse_qs testcase is a two-tuple that contains
@@ -68,16 +62,10 @@ parse_qs_test_cases = [
     (b"&a=b", {b'a': [b'b']}),
     (b"a=a+b&b=b+c", {b'a': [b'a b'], b'b': [b'b c']}),
     (b"a=1&a=2", {b'a': [b'1', b'2']}),
-    (";", {}),
-    (";;", {}),
-    (";a=b", {'a': ['b']}),
-    ("a=a+b;b=b+c", {'a': ['a b'], 'b': ['b c']}),
-    ("a=1;a=2", {'a': ['1', '2']}),
-    (b";", {}),
-    (b";;", {}),
-    (b";a=b", {b'a': [b'b']}),
-    (b"a=a+b;b=b+c", {b'a': [b'a b'], b'b': [b'b c']}),
-    (b"a=1;a=2", {b'a': [b'1', b'2']}),
+    (";a=b", {';a': ['b']}),
+    ("a=a+b;b=b+c", {'a': ['a b;b=b c']}),
+    (b";a=b", {b';a': [b'b']}),
+    (b"a=a+b;b=b+c", {b'a':[ b'a b;b=b c']}),
 ]
 
 class UrlParseTestCase(unittest.TestCase):
@@ -884,10 +872,46 @@ class UrlParseTestCase(unittest.TestCase):
     def test_parse_qsl_max_num_fields(self):
         with self.assertRaises(ValueError):
             urllib.parse.parse_qs('&'.join(['a=a']*11), max_num_fields=10)
-        with self.assertRaises(ValueError):
-            urllib.parse.parse_qs(';'.join(['a=a']*11), max_num_fields=10)
         urllib.parse.parse_qs('&'.join(['a=a']*10), max_num_fields=10)
 
+    def test_parse_qs_separator(self):
+        parse_qs_semicolon_cases = [
+            (";", {}),
+            (";;", {}),
+            (";a=b", {'a': ['b']}),
+            ("a=a+b;b=b+c", {'a': ['a b'], 'b': ['b c']}),
+            ("a=1;a=2", {'a': ['1', '2']}),
+            (b";", {}),
+            (b";;", {}),
+            (b";a=b", {b'a': [b'b']}),
+            (b"a=a+b;b=b+c", {b'a': [b'a b'], b'b': [b'b c']}),
+            (b"a=1;a=2", {b'a': [b'1', b'2']}),
+        ]
+        for orig, expect in parse_qs_semicolon_cases:
+            with self.subTest(f"Original: {orig!r}, Expected: {expect!r}"):
+                result = urllib.parse.parse_qs(orig, separator=';')
+                self.assertEqual(result, expect, "Error parsing %r" % orig)
+
+
+    def test_parse_qsl_separator(self):
+        parse_qsl_semicolon_cases = [
+            (";", []),
+            (";;", []),
+            (";a=b", [('a', 'b')]),
+            ("a=a+b;b=b+c", [('a', 'a b'), ('b', 'b c')]),
+            ("a=1;a=2", [('a', '1'), ('a', '2')]),
+            (b";", []),
+            (b";;", []),
+            (b";a=b", [(b'a', b'b')]),
+            (b"a=a+b;b=b+c", [(b'a', b'a b'), (b'b', b'b c')]),
+            (b"a=1;a=2", [(b'a', b'1'), (b'a', b'2')]),
+        ]
+        for orig, expect in parse_qsl_semicolon_cases:
+            with self.subTest(f"Original: {orig!r}, Expected: {expect!r}"):
+                result = urllib.parse.parse_qsl(orig, separator=';')
+                self.assertEqual(result, expect, "Error parsing %r" % orig)
+
+
     def test_urlencode_sequences(self):
         # Other tests incidentally urlencode things; test non-covered cases:
         # Sequence and object values.
diff --git a/lib-python/3/urllib/parse.py b/lib-python/3/urllib/parse.py
index fa8827a..66056bf 100644
--- a/lib-python/3/urllib/parse.py
+++ b/lib-python/3/urllib/parse.py
@@ -644,7 +644,7 @@ def unquote(string, encoding='utf-8', errors='replace'):
 
 
 def parse_qs(qs, keep_blank_values=False, strict_parsing=False,
-             encoding='utf-8', errors='replace', max_num_fields=None):
+             encoding='utf-8', errors='replace', max_num_fields=None, separator='&'):
     """Parse a query given as a string argument.
 
         Arguments:
@@ -668,12 +668,15 @@ def parse_qs(qs, keep_blank_values=False, strict_parsing=False,
         max_num_fields: int. If set, then throws a ValueError if there
             are more than n fields read by parse_qsl().
 
+        separator: str. The symbol to use for separating the query arguments.
+            Defaults to &.
+
         Returns a dictionary.
     """
     parsed_result = {}
     pairs = parse_qsl(qs, keep_blank_values, strict_parsing,
                       encoding=encoding, errors=errors,
-                      max_num_fields=max_num_fields)
+                      max_num_fields=max_num_fields, separator=separator)
     for name, value in pairs:
         if name in parsed_result:
             parsed_result[name].append(value)
@@ -683,7 +686,7 @@ def parse_qs(qs, keep_blank_values=False, strict_parsing=False,
 
 
 def parse_qsl(qs, keep_blank_values=False, strict_parsing=False,
-              encoding='utf-8', errors='replace', max_num_fields=None):
+              encoding='utf-8', errors='replace', max_num_fields=None, separator='&'):
     """Parse a query given as a string argument.
 
         Arguments:
@@ -706,19 +709,25 @@ def parse_qsl(qs, keep_blank_values=False, strict_parsing=False,
         max_num_fields: int. If set, then throws a ValueError
             if there are more than n fields read by parse_qsl().
 
+        separator: str. The symbol to use for separating the query arguments.
+            Defaults to &.
+
         Returns a list, as G-d intended.
     """
     qs, _coerce_result = _coerce_args(qs)
 
+    if not separator or (not isinstance(separator, (str, bytes))):
+        raise ValueError("Separator must be of type string or bytes.")
+
     # If max_num_fields is defined then check that the number of fields
     # is less than max_num_fields. This prevents a memory exhaustion DOS
     # attack via post bodies with many fields.
     if max_num_fields is not None:
-        num_fields = 1 + qs.count('&') + qs.count(';')
+        num_fields = 1 + qs.count(separator)
         if max_num_fields < num_fields:
             raise ValueError('Max number of fields exceeded')
 
-    pairs = [s2 for s1 in qs.split('&') for s2 in s1.split(';')]
+    pairs = [s1 for s1 in qs.split(separator)]
     r = []
     for name_value in pairs:
         if not name_value and not strict_parsing:
