[3.6] bpo-42967: only use '&' as a query string separator (GH-24297) (GH-24532)

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>

Author: 4 people

Doc/library/cgi.rst

@@ -277,13 +277,12 @@ These are useful if you want more control, or if you want to employ some of the
 algorithms implemented in this module in other circumstances.
 
 
-.. function:: parse(fp=None, environ=os.environ, keep_blank_values=False, strict_parsing=False)
+.. function:: parse(fp=None, environ=os.environ, keep_blank_values=False, strict_parsing=False, separator="&")
 
  Parse a query in the environment or from a file (the file defaults to
- ``sys.stdin``). The *keep_blank_values* and *strict_parsing* parameters are
+ ``sys.stdin``). The *keep_blank_values*, *strict_parsing* and *separator* parameters are
  passed to :func:`urllib.parse.parse_qs` unchanged.
 
-
 .. function:: parse_qs(qs, keep_blank_values=False, strict_parsing=False)
 
  This function is deprecated in this module. Use :func:`urllib.parse.parse_qs`
@@ -308,6 +307,9 @@ algorithms implemented in this module in other circumstances.
  Note that this does not parse nested multipart parts --- use
  :class:`FieldStorage` for that.
 
+ .. versionchanged:: 3.6.13
+ Added the *separator* parameter.
+
 
 .. function:: parse_header(string)
 

Doc/library/urllib.parse.rst

@@ -143,7 +143,7 @@ or on combining URL components into a URL string.
  now raise :exc:`ValueError`.
 
 
-.. function:: parse_qs(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None)
+.. function:: parse_qs(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None, separator='&')
 
  Parse a query string given as a string argument (data of type
  :mimetype:`application/x-www-form-urlencoded`). Data are returned as a
@@ -168,6 +168,9 @@ or on combining URL components into a URL string.
  read. If set, then throws a :exc:`ValueError` if there are more than
  *max_num_fields* fields read.
 
+ The optional argument *separator* is the symbol to use for separating the
+ query arguments. It defaults to ``&``.
+
  Use the :func:`urllib.parse.urlencode` function (with the ``doseq``
  parameter set to ``True``) to convert such dictionaries into query
  strings.
@@ -179,8 +182,14 @@ or on combining URL components into a URL string.
  .. versionchanged:: 3.6.8
  Added *max_num_fields* parameter.
 
+ .. versionchanged:: 3.6.13
+ Added *separator* parameter with the default value of ``&``. Python
+ versions earlier than Python 3.6.13 allowed using both ``;`` and ``&`` as
+ query parameter separator. This has been changed to allow only a single
+ separator key, with ``&`` as the default separator.
+
 
-.. function:: parse_qsl(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None)
+.. function:: parse_qsl(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None, separator='&')
 
  Parse a query string given as a string argument (data of type
  :mimetype:`application/x-www-form-urlencoded`). Data are returned as a list of
@@ -204,6 +213,9 @@ or on combining URL components into a URL string.
  read. If set, then throws a :exc:`ValueError` if there are more than
  *max_num_fields* fields read.
 
+ The optional argument *separator* is the symbol to use for separating the
+ query arguments. It defaults to ``&``.
+
  Use the :func:`urllib.parse.urlencode` function to convert such lists of pairs into
  query strings.
 
@@ -213,6 +225,12 @@ or on combining URL components into a URL string.
  .. versionchanged:: 3.6.8
  Added *max_num_fields* parameter.
 
+ .. versionchanged:: 3.6.13
+ Added *separator* parameter with the default value of ``&``. Python
+ versions earlier than Python 3.6.13 allowed using both ``;`` and ``&`` as
+ query parameter separator. This has been changed to allow only a single
+ separator key, with ``&`` as the default separator.
+
 
 .. function:: urlunparse(parts)
 

Doc/whatsnew/3.6.rst

@@ -2459,3 +2459,16 @@ because of the behavior of the socket option ``SO_REUSEADDR`` in UDP. For more
 details, see the documentation for ``loop.create_datagram_endpoint()``.
 (Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in
 :issue:`37228`.)
+
+Notable changes in Python 3.6.13
+================================
+
+Earlier Python versions allowed using both ``;`` and ``&`` as
+query parameter separators in :func:`urllib.parse.parse_qs` and
+:func:`urllib.parse.parse_qsl`. Due to security concerns, and to conform with
+newer W3C recommendations, this has been changed to allow only a single
+separator key, with ``&`` as the default. This change also affects
+:func:`cgi.parse` and :func:`cgi.parse_multipart` as they use the affected
+functions internally. For more details, please see their respective
+documentation.
+(Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in :issue:`42967`.)

Lib/cgi.py

@@ -117,7 +117,8 @@ def closelog():
 # 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 @@ def __init__(self, fp=None, headers=None, outerboundary=b'',
  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 @@ def read_urlencoded(self):
  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 @@ def read_multi(self, environ, keep_blank_values, strict_parsing):
  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 @@ def read_multi(self, environ, keep_blank_values, strict_parsing):
 
  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

Lib/test/test_cgi.py

@@ -55,12 +55,9 @@ def do_test(buf, method):
  ("", 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 @@ def do_test(buf, method):
  ("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 @@ def test_strict(self):
  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")
 

Lib/test/test_urlparse.py

@@ -32,16 +32,10 @@
  (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 @@
  (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 @@ def test_parse_qsl_encoding(self):
  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.

Lib/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:

Misc/NEWS.d/next/Security/2021-02-14-15-59-16.bpo-42967.YApqDS.rst

@@ -0,0 +1 @@
+Fix web cache poisoning vulnerability by defaulting the query args separator to ``&``, and allowing the user to choose a custom separator.