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bpo-36384: Leading zeros in IPv4 addresses are no longer tolerated (GH-25099)
Reverts commit e653d4d and makes parsing even more strict. Like socket.inet_pton() any leading zero is now treated as invalid input. Signed-off-by: Christian Heimes <christian@python.org> Co-authored-by: Łukasz Langa <lukasz@langa.pl>
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6 files changed

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‎Doc/library/ipaddress.rst‎

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@@ -104,8 +104,7 @@ write code that handles both IP versions correctly. Address objects are
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1. A string in decimal-dot notation, consisting of four decimal integers in
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the inclusive range 0--255, separated by dots (e.g. ``192.168.0.1``). Each
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integer represents an octet (byte) in the address. Leading zeroes are
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tolerated only for values less than 8 (as there is no ambiguity
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between the decimal and octal interpretations of such strings).
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not tolerated to prevent confusion with octal notation.
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2. An integer that fits into 32 bits.
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3. An integer packed into a :class:`bytes` object of length 4 (most
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significant octet first).
@@ -117,6 +116,22 @@ write code that handles both IP versions correctly. Address objects are
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>>> ipaddress.IPv4Address(b'\xC0\xA8\x00\x01')
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IPv4Address('192.168.0.1')
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.. versionchanged:: 3.8
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Leading zeros are tolerated, even in ambiguous cases that look like
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octal notation.
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.. versionchanged:: 3.10
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Leading zeros are no longer tolerated and are treated as an error.
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IPv4 address strings are now parsed as strict as glibc
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:func:`~socket.inet_pton`.
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.. versionchanged:: 3.9.5
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The above change was also included in Python 3.9 starting with
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version 3.9.5.
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.. attribute:: version
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The appropriate version number: ``4`` for IPv4, ``6`` for IPv6.

‎Doc/tools/susp-ignored.csv‎

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@@ -149,8 +149,8 @@ library/ipaddress,,:db8,>>> ipaddress.IPv6Address('2001:db8::1000')
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library/ipaddress,,::,>>> ipaddress.IPv6Address('2001:db8::1000')
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library/ipaddress,,:db8,'2001:db8::1000'
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library/ipaddress,,::,'2001:db8::1000'
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library/ipaddress,231,:db8,">>> f'{ipaddress.IPv6Address(""2001:db8::1000""):s}'"
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library/ipaddress,231,::,">>> f'{ipaddress.IPv6Address(""2001:db8::1000""):s}'"
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library/ipaddress,,:db8,">>> f'{ipaddress.IPv6Address(""2001:db8::1000""):s}'"
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library/ipaddress,,::,">>> f'{ipaddress.IPv6Address(""2001:db8::1000""):s}'"
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library/ipaddress,,::,IPv6Address('ff02::5678%1')
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library/ipaddress,,::,fe80::1234
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library/ipaddress,,:db8,">>> ipaddress.ip_address(""2001:db8::1"").reverse_pointer"

‎Doc/whatsnew/3.9.rst‎

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@@ -537,6 +537,10 @@ Scoped IPv6 addresses can be parsed using :class:`ipaddress.IPv6Address`.
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If present, scope zone ID is available through the :attr:`~ipaddress.IPv6Address.scope_id` attribute.
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(Contributed by Oleksandr Pavliuk in :issue:`34788`.)
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Starting with Python 3.9.5 the :mod:`ipaddress` module no longer
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accepts any leading zeros in IPv4 address strings.
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(Contributed by Christian Heimes in :issue:`36384`).
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math
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----
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@@ -1114,6 +1118,14 @@ Changes in the Python API
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compatible classes that don't inherit from those mentioned types.
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(Contributed by Roger Aiudi in :issue:`34775`).
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* Starting with Python 3.9.5 the :mod:`ipaddress` module no longer
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accepts any leading zeros in IPv4 address strings. Leading zeros are
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ambiguous and interpreted as octal notation by some libraries. For example
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the legacy function :func:`socket.inet_aton` treats leading zeros as octal
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notatation. glibc implementation of modern :func:`~socket.inet_pton` does
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not accept any leading zeros.
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(Contributed by Christian Heimes in :issue:`36384`).
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* :func:`codecs.lookup` now normalizes the encoding name the same way as
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:func:`encodings.normalize_encoding`, except that :func:`codecs.lookup` also
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converts the name to lower case. For example, ``"latex+latin1"`` encoding

‎Lib/ipaddress.py‎

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@@ -1223,6 +1223,11 @@ def _parse_octet(cls, octet_str):
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if len(octet_str) > 3:
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msg = "At most 3 characters permitted in %r"
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raise ValueError(msg % octet_str)
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# Handle leading zeros as strict as glibc's inet_pton()
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# See security bug bpo-36384
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if octet_str != '0' and octet_str[0] == '0':
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msg = "Leading zeros are not permitted in %r"
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raise ValueError(msg % octet_str)
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# Convert to integer (we know digits are legal)
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octet_int = int(octet_str, 10)
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if octet_int > 255:

‎Lib/test/test_ipaddress.py‎

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@@ -96,10 +96,23 @@ def pickle_test(self, addr):
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class CommonTestMixin_v4(CommonTestMixin):
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def test_leading_zeros(self):
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self.assertInstancesEqual("000.000.000.000", "0.0.0.0")
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self.assertInstancesEqual("192.168.000.001", "192.168.0.1")
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self.assertInstancesEqual("016.016.016.016", "16.16.16.16")
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self.assertInstancesEqual("001.000.008.016", "1.0.8.16")
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# bpo-36384: no leading zeros to avoid ambiguity with octal notation
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msg = "Leading zeros are not permitted in '\d+'"
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addresses = [
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"000.000.000.000",
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"192.168.000.001",
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"016.016.016.016",
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"192.168.000.001",
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"001.000.008.016",
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"01.2.3.40",
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"1.02.3.40",
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"1.2.03.40",
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"1.2.3.040",
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]
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for address in addresses:
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with self.subTest(address=address):
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with self.assertAddressError(msg):
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self.factory(address)
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def test_int(self):
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self.assertInstancesEqual(0, "0.0.0.0")

‎Misc/NEWS.d/next/Security/2021-03-30-16-29-51.bpo-36384.sCAmLs.rst‎

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:mod:`ipaddress` module no longer accepts any leading zeros in IPv4 address
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strings. Leading zeros are ambiguous and interpreted as octal notation by
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some libraries. For example the legacy function :func:`socket.inet_aton`
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treats leading zeros as octal notatation. glibc implementation of modern
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:func:`~socket.inet_pton` does not accept any leading zeros. For a while
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the :mod:`ipaddress` module used to accept ambiguous leading zeros.

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