From e7b005c05dbdbce967a409abd71641281a8604bf Mon Sep 17 00:00:00 2001
From: Senthil Kumaran <senthil@uthcode.com>
Date: Mon, 15 Feb 2021 11:16:43 -0800
Subject: [PATCH 24/24] [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>

Rebased for Python 2.7 by Michał Górny
---
 Doc/library/cgi.rst                           |  7 +++-
 Doc/library/urlparse.rst                      | 23 ++++++++++-
 Lib/cgi.py                                    | 20 +++++++---
 Lib/test/test_cgi.py                          | 29 +++++++++++---
 Lib/test/test_urlparse.py                     | 38 +++++++++----------
 Lib/urlparse.py                               | 22 ++++++++---
 .../2021-02-14-15-59-16.bpo-42967.YApqDS.rst  |  1 +
 7 files changed, 100 insertions(+), 40 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Security/2021-02-14-15-59-16.bpo-42967.YApqDS.rst

diff --git a/Doc/library/cgi.rst b/Doc/library/cgi.rst
index ecd62c8c01..b85cdd8b61 100644
--- a/Doc/library/cgi.rst
+++ b/Doc/library/cgi.rst
@@ -285,10 +285,10 @@ 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[, environ[, keep_blank_values[, strict_parsing]]])
+.. function:: parse(fp[, environ[, keep_blank_values[, strict_parsing]]], separator="&")
 
    Parse a query in the environment or from a file (the file defaults to
-   ``sys.stdin`` and environment defaults to ``os.environ``).  The *keep_blank_values* and *strict_parsing* parameters are
+   ``sys.stdin`` and environment defaults to ``os.environ``).  The *keep_blank_values*, *strict_parsing* and *separator* parameters are
    passed to :func:`urlparse.parse_qs` unchanged.
 
 
@@ -316,6 +316,9 @@ 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)
 
diff --git a/Doc/library/urlparse.rst b/Doc/library/urlparse.rst
index 0989c88c30..2f8e4c5a44 100644
--- a/Doc/library/urlparse.rst
+++ b/Doc/library/urlparse.rst
@@ -136,7 +136,7 @@ The :mod:`urlparse` module defines the following functions:
       now raise :exc:`ValueError`.
 
 
-.. function:: parse_qs(qs[, keep_blank_values[, strict_parsing[, max_num_fields]]])
+.. function:: parse_qs(qs[, keep_blank_values[, strict_parsing[, max_num_fields]]], separator='&')
 
    Parse a query string given as a string argument (data of type
    :mimetype:`application/x-www-form-urlencoded`).  Data are returned as a
@@ -157,6 +157,9 @@ The :mod:`urlparse` module defines the following functions:
    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.urlencode` function to convert such dictionaries into
    query strings.
 
@@ -166,7 +169,14 @@ The :mod:`urlparse` module defines the following functions:
    .. versionchanged:: 2.7.16
       Added *max_num_fields* parameter.
 
-.. function:: parse_qsl(qs[, keep_blank_values[, strict_parsing[, max_num_fields]]])
+   .. versionchanged:: 2.7.18-gentoo
+      Added *separator* parameter with the default value of ``&``. Earlier
+      Python versions 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[, strict_parsing[, max_num_fields]]], 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
@@ -186,6 +196,9 @@ The :mod:`urlparse` module defines the following functions:
    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.urlencode` function to convert such lists of pairs into
    query strings.
 
@@ -195,6 +208,12 @@ The :mod:`urlparse` module defines the following functions:
    .. versionchanged:: 2.7.16
       Added *max_num_fields* parameter.
 
+   .. versionchanged:: 2.7.18-gentoo
+      Added *separator* parameter with the default value of ``&``. Earlier
+      Python versions 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)
 
    Construct a URL from a tuple as returned by ``urlparse()``. The *parts* argument
diff --git a/Lib/cgi.py b/Lib/cgi.py
index 5b903e0347..9d0848b6b1 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -121,7 +121,8 @@ 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:
@@ -140,6 +141,9 @@ 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
@@ -171,7 +175,8 @@ def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
         else:
             qs = ""
         environ['QUERY_STRING'] = qs    # XXX Shouldn't, really
-    return urlparse.parse_qs(qs, keep_blank_values, strict_parsing)
+    return urlparse.parse_qs(qs, keep_blank_values, strict_parsing,
+                             separator=separator)
 
 
 # parse query string function called from urlparse,
@@ -395,7 +400,7 @@ class FieldStorage:
 
     def __init__(self, fp=None, headers=None, outerboundary="",
                  environ=os.environ, keep_blank_values=0, strict_parsing=0,
-                 max_num_fields=None):
+                 max_num_fields=None, separator='&'):
         """Constructor.  Read multipart/* until last part.
 
         Arguments, all optional:
@@ -430,6 +435,7 @@ 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
@@ -613,7 +619,8 @@ class FieldStorage:
         if self.qs_on_post:
             qs += '&' + self.qs_on_post
         query = urlparse.parse_qsl(qs, self.keep_blank_values,
-                                   self.strict_parsing, self.max_num_fields)
+                                   self.strict_parsing, self.max_num_fields,
+                                   separator=self.separator)
         self.list = [MiniFieldStorage(key, value) for key, value in query]
         self.skip_lines()
 
@@ -629,7 +636,8 @@ class FieldStorage:
             query = urlparse.parse_qsl(self.qs_on_post,
                                        self.keep_blank_values,
                                        self.strict_parsing,
-                                       self.max_num_fields)
+                                       self.max_num_fields,
+                                       separator=self.separator)
             self.list.extend(MiniFieldStorage(key, value)
                              for key, value in query)
             FieldStorageClass = None
@@ -649,7 +657,7 @@ class FieldStorage:
             headers = rfc822.Message(self.fp)
             part = klass(self.fp, headers, ib,
                          environ, keep_blank_values, strict_parsing,
-                         max_num_fields)
+                         max_num_fields, separator=self.separator)
 
             if max_num_fields is not None:
                 max_num_fields -= 1
diff --git a/Lib/test/test_cgi.py b/Lib/test/test_cgi.py
index 743c2afbd4..f414faa23b 100644
--- a/Lib/test/test_cgi.py
+++ b/Lib/test/test_cgi.py
@@ -61,12 +61,9 @@ 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: ''")),
@@ -81,8 +78,6 @@ 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'],
@@ -188,6 +183,30 @@ class CgiTests(unittest.TestCase):
             self.assertEqual(expect[k], v)
         self.assertItemsEqual(expect.values(), d.values())
 
+    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/test/test_urlparse.py b/Lib/test/test_urlparse.py
index 86c4a0595c..0b2107339a 100644
--- a/Lib/test/test_urlparse.py
+++ b/Lib/test/test_urlparse.py
@@ -24,16 +24,20 @@ parse_qsl_test_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')]),
-    (";", []),
-    (";;", []),
-    (";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')]),
+    (b"", []),
+    (b"&", []),
+    (b"&&", []),
+    (b"=", [(b'', b'')]),
+    (b"=a", [(b'', b'a')]),
+    (b"a", [(b'a', b'')]),
+    (b"a=", [(b'a', 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')]),
 ]
 
 parse_qs_test_cases = [
@@ -57,16 +61,10 @@ 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):
diff --git a/Lib/urlparse.py b/Lib/urlparse.py
index 798b467b60..6c32727fce 100644
--- a/Lib/urlparse.py
+++ b/Lib/urlparse.py
@@ -382,7 +382,8 @@ def unquote(s):
             append(item)
     return ''.join(res)
 
-def parse_qs(qs, keep_blank_values=0, strict_parsing=0, max_num_fields=None):
+def parse_qs(qs, keep_blank_values=0, strict_parsing=0, max_num_fields=None,
+             separator='&'):
     """Parse a query given as a string argument.
 
         Arguments:
@@ -402,17 +403,22 @@ def parse_qs(qs, keep_blank_values=0, strict_parsing=0, max_num_fields=None):
 
         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 &.
+
     """
     dict = {}
     for name, value in parse_qsl(qs, keep_blank_values, strict_parsing,
-                                 max_num_fields):
+                                 max_num_fields, separator=separator):
         if name in dict:
             dict[name].append(value)
         else:
             dict[name] = [value]
     return dict
 
-def parse_qsl(qs, keep_blank_values=0, strict_parsing=0, max_num_fields=None):
+def parse_qsl(qs, keep_blank_values=0, strict_parsing=0, max_num_fields=None,
+              separator='&'):
     """Parse a query given as a string argument.
 
     Arguments:
@@ -432,17 +438,23 @@ def parse_qsl(qs, keep_blank_values=0, strict_parsing=0, max_num_fields=None):
     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.
     """
+    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:
diff --git a/Misc/NEWS.d/next/Security/2021-02-14-15-59-16.bpo-42967.YApqDS.rst b/Misc/NEWS.d/next/Security/2021-02-14-15-59-16.bpo-42967.YApqDS.rst
new file mode 100644
index 0000000000..f08489b414
--- /dev/null
+++ b/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.
-- 
2.30.1

