CVE-2024-56374

@@ -30,7 +30,7 @@
 )
 from django.utils.duration import duration_microseconds, duration_string
 from django.utils.functional import Promise, cached_property
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.itercompat import is_iterable
 from django.utils.text import capfirst
 from django.utils.translation import gettext_lazy as _
@@ -2220,7 +2220,7 @@ def __init__(
             invalid_error_message,
         ) = validators.ip_address_validators(protocol, unpack_ipv4)
         self.default_error_messages["invalid"] = invalid_error_message
-        kwargs["max_length"] = 39
+        kwargs["max_length"] = MAX_IPV6_ADDRESS_LENGTH
         super().__init__(verbose_name, name, *args, **kwargs)
 
     def check(self, **kwargs):
@@ -2247,7 +2247,7 @@ def deconstruct(self):
             kwargs["unpack_ipv4"] = self.unpack_ipv4
         if self.protocol != "both":
             kwargs["protocol"] = self.protocol
-        if kwargs.get("max_length") == 39:
+        if kwargs.get("max_length") == self.max_length:
             del kwargs["max_length"]
         return name, path, args, kwargs
 

@@ -46,7 +46,7 @@
 from django.utils.dateparse import parse_datetime, parse_duration
 from django.utils.deprecation import RemovedInDjango60Warning
 from django.utils.duration import duration_string
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.regex_helper import _lazy_re_compile
 from django.utils.translation import gettext_lazy as _
 from django.utils.translation import ngettext_lazy
@@ -1295,14 +1295,17 @@ def __init__(self, *, protocol="both", unpack_ipv4=False, **kwargs):
         self.default_validators = validators.ip_address_validators(
             protocol, unpack_ipv4
         )[0]
+        kwargs.setdefault("max_length", MAX_IPV6_ADDRESS_LENGTH)
         super().__init__(**kwargs)
 
     def to_python(self, value):
         if value in self.empty_values:
             return ""
         value = value.strip()
         if value and ":" in value:
-            return clean_ipv6_address(value, self.unpack_ipv4)
+            return clean_ipv6_address(
+                value, self.unpack_ipv4, max_length=self.max_length
+            )
         return value
 
 

@@ -3,9 +3,22 @@
 from django.core.exceptions import ValidationError
 from django.utils.translation import gettext_lazy as _
 
+MAX_IPV6_ADDRESS_LENGTH = 39
+
+
+def _ipv6_address_from_str(ip_str, max_length=MAX_IPV6_ADDRESS_LENGTH):
+    if len(ip_str) > max_length:
+        raise ValueError(
+            f"Unable to convert {ip_str} to an IPv6 address (value too long)."
+        )
+    return ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+
 
 def clean_ipv6_address(
-    ip_str, unpack_ipv4=False, error_message=_("This is not a valid IPv6 address.")
+    ip_str,
+    unpack_ipv4=False,
+    error_message=_("This is not a valid IPv6 address."),
+    max_length=MAX_IPV6_ADDRESS_LENGTH,
 ):
     """
     Clean an IPv6 address string.
@@ -24,7 +37,7 @@ def clean_ipv6_address(
     Return a compressed IPv6 address or the same value.
     """
     try:
-        addr = ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+        addr = _ipv6_address_from_str(ip_str, max_length)
     except ValueError:
         raise ValidationError(error_message, code="invalid")
 
@@ -41,7 +54,7 @@ def is_valid_ipv6_address(ip_str):
     Return whether or not the `ip_str` string is a valid IPv6 address.
     """
     try:
-        ipaddress.IPv6Address(ip_str)
+        _ipv6_address_from_str(ip_str)
     except ValueError:
         return False
     return True

@@ -774,15 +774,15 @@ For each field, we describe the default widget used if you don't specify
     * Empty value: ``''`` (an empty string)
     * Normalizes to: A string. IPv6 addresses are normalized as described below.
     * Validates that the given value is a valid IP address.
-    * Error message keys: ``required``, ``invalid``
+    * Error message keys: ``required``, ``invalid``, ``max_length``
 
     The IPv6 address normalization follows :rfc:`4291#section-2.2` section 2.2,
     including using the IPv4 format suggested in paragraph 3 of that section, like
     ``::ffff:192.0.2.0``. For example, ``2001:0::0:01`` would be normalized to
     ``2001::1``, and ``::ffff:0a0a:0a0a`` to ``::ffff:10.10.10.10``. All characters
     are converted to lowercase.
 
-    Takes two optional arguments:
+    Takes three optional arguments:
 
     .. attribute:: protocol
 
@@ -797,6 +797,15 @@ For each field, we describe the default widget used if you don't specify
         ``192.0.2.1``. Default is disabled. Can only be used
         when ``protocol`` is set to ``'both'``.
 
+    .. attribute:: max_length
+
+        Defaults to 39, and behaves the same way as it does for
+        :class:`CharField`.
+
+    .. versionchanged:: 4.2.18
+
+        The default value for ``max_length`` was set to 39 characters.
+
 ``ImageField``
 --------------
 

@@ -5,3 +5,15 @@ Django 4.2.18 release notes
 *January 14, 2025*
 
 Django 4.2.18 fixes a security issue with severity "moderate" in 4.2.17.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -5,3 +5,15 @@ Django 5.0.11 release notes
 *January 14, 2025*
 
 Django 5.0.11 fixes a security issue with severity "moderate" in 5.0.10.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -1,6 +1,7 @@
 from django.core.exceptions import ValidationError
 from django.forms import GenericIPAddressField
 from django.test import SimpleTestCase
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH
 
 
 class GenericIPAddressFieldTest(SimpleTestCase):
@@ -125,6 +126,35 @@ def test_generic_ipaddress_as_ipv6_only(self):
         ):
             f.clean("1:2")
 
+    def test_generic_ipaddress_max_length_custom(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+        f = GenericIPAddressField(max_length=len(addr))
+        f.clean(addr)
+
+    def test_generic_ipaddress_max_length_validation_error(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+
+        cases = [
+            ({}, MAX_IPV6_ADDRESS_LENGTH),  # Default value.
+            ({"max_length": len(addr) - 1}, len(addr) - 1),
+        ]
+        for kwargs, max_length in cases:
+            max_length_plus_one = max_length + 1
+            msg = (
+                f"Ensure this value has at most {max_length} characters (it has "
+                f"{max_length_plus_one}).'"
+            )
+            with self.subTest(max_length=max_length):
+                f = GenericIPAddressField(**kwargs)
+                with self.assertRaisesMessage(ValidationError, msg):
+                    f.clean("x" * max_length_plus_one)
+                with self.assertRaisesMessage(
+                    ValidationError, "This is not a valid IPv6 address."
+                ):
+                    f.clean(addr)
+
     def test_generic_ipaddress_as_generic_not_required(self):
         f = GenericIPAddressField(required=False)
         self.assertEqual(f.clean(""), "")
@@ -150,7 +180,8 @@ def test_generic_ipaddress_as_generic_not_required(self):
             f.clean(" fe80::223:6cff:fe8a:2e8a "), "fe80::223:6cff:fe8a:2e8a"
         )
         self.assertEqual(
-            f.clean(" 2a02::223:6cff:fe8a:2e8a "), "2a02::223:6cff:fe8a:2e8a"
+            f.clean(" " * MAX_IPV6_ADDRESS_LENGTH + " 2a02::223:6cff:fe8a:2e8a "),
+            "2a02::223:6cff:fe8a:2e8a",
         )
         with self.assertRaisesMessage(
             ValidationError, "'This is not a valid IPv6 address.'"

@@ -1,9 +1,16 @@
-import unittest
+import traceback
+from io import StringIO
 
-from django.utils.ipv6 import clean_ipv6_address, is_valid_ipv6_address
+from django.core.exceptions import ValidationError
+from django.test import SimpleTestCase
+from django.utils.ipv6 import (
+    MAX_IPV6_ADDRESS_LENGTH,
+    clean_ipv6_address,
+    is_valid_ipv6_address,
+)
 
 
-class TestUtilsIPv6(unittest.TestCase):
+class TestUtilsIPv6(SimpleTestCase):
     def test_validates_correct_plain_address(self):
         self.assertTrue(is_valid_ipv6_address("fe80::223:6cff:fe8a:2e8a"))
         self.assertTrue(is_valid_ipv6_address("2a02::223:6cff:fe8a:2e8a"))
@@ -64,3 +71,21 @@ def test_unpacks_ipv4(self):
         self.assertEqual(
             clean_ipv6_address("::ffff:18.52.18.52", unpack_ipv4=True), "18.52.18.52"
         )
+
+    def test_address_too_long(self):
+        addresses = [
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228",  # IPv4-mapped IPv6 address
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228%123456",  # % scope/zone
+            "fe80::223:6cff:fe8a:2e8a:1234:5678:00000",  # MAX_IPV6_ADDRESS_LENGTH + 1
+        ]
+        msg = "This is the error message."
+        value_error_msg = "Unable to convert %s to an IPv6 address (value too long)."
+        for addr in addresses:
+            with self.subTest(addr=addr):
+                self.assertGreater(len(addr), MAX_IPV6_ADDRESS_LENGTH)
+                self.assertEqual(is_valid_ipv6_address(addr), False)
+                with self.assertRaisesMessage(ValidationError, msg) as ctx:
+                    clean_ipv6_address(addr, error_message=msg)
+                exception_traceback = StringIO()
+                traceback.print_exception(ctx.exception, file=exception_traceback)
+                self.assertIn(value_error_msg % addr, exception_traceback.getvalue())

@@ -25,7 +25,7 @@
 )
 from django.utils.duration import duration_microseconds, duration_string
 from django.utils.functional import Promise, cached_property
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.itercompat import is_iterable
 from django.utils.text import capfirst
 from django.utils.translation import gettext_lazy as _
@@ -2160,7 +2160,7 @@ def __init__(
             invalid_error_message,
         ) = validators.ip_address_validators(protocol, unpack_ipv4)
         self.default_error_messages["invalid"] = invalid_error_message
-        kwargs["max_length"] = 39
+        kwargs["max_length"] = MAX_IPV6_ADDRESS_LENGTH
         super().__init__(verbose_name, name, *args, **kwargs)
 
     def check(self, **kwargs):
@@ -2187,7 +2187,7 @@ def deconstruct(self):
             kwargs["unpack_ipv4"] = self.unpack_ipv4
         if self.protocol != "both":
             kwargs["protocol"] = self.protocol
-        if kwargs.get("max_length") == 39:
+        if kwargs.get("max_length") == self.max_length:
             del kwargs["max_length"]
         return name, path, args, kwargs
 

@@ -42,7 +42,7 @@
 from django.utils import formats
 from django.utils.dateparse import parse_datetime, parse_duration
 from django.utils.duration import duration_string
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.regex_helper import _lazy_re_compile
 from django.utils.translation import gettext_lazy as _
 from django.utils.translation import ngettext_lazy
@@ -1284,14 +1284,17 @@ def __init__(self, *, protocol="both", unpack_ipv4=False, **kwargs):
         self.default_validators = validators.ip_address_validators(
             protocol, unpack_ipv4
         )[0]
+        kwargs.setdefault("max_length", MAX_IPV6_ADDRESS_LENGTH)
         super().__init__(**kwargs)
 
     def to_python(self, value):
         if value in self.empty_values:
             return ""
         value = value.strip()
         if value and ":" in value:
-            return clean_ipv6_address(value, self.unpack_ipv4)
+            return clean_ipv6_address(
+                value, self.unpack_ipv4, max_length=self.max_length
+            )
         return value
 
 

@@ -3,9 +3,22 @@
 from django.core.exceptions import ValidationError
 from django.utils.translation import gettext_lazy as _
 
+MAX_IPV6_ADDRESS_LENGTH = 39
+
+
+def _ipv6_address_from_str(ip_str, max_length=MAX_IPV6_ADDRESS_LENGTH):
+    if len(ip_str) > max_length:
+        raise ValueError(
+            f"Unable to convert {ip_str} to an IPv6 address (value too long)."
+        )
+    return ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+
 
 def clean_ipv6_address(
-    ip_str, unpack_ipv4=False, error_message=_("This is not a valid IPv6 address.")
+    ip_str,
+    unpack_ipv4=False,
+    error_message=_("This is not a valid IPv6 address."),
+    max_length=MAX_IPV6_ADDRESS_LENGTH,
 ):
     """
     Clean an IPv6 address string.
@@ -24,7 +37,7 @@ def clean_ipv6_address(
     Return a compressed IPv6 address or the same value.
     """
     try:
-        addr = ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+        addr = _ipv6_address_from_str(ip_str, max_length)
     except ValueError:
         raise ValidationError(error_message, code="invalid")
 
@@ -41,7 +54,7 @@ def is_valid_ipv6_address(ip_str):
     Return whether or not the `ip_str` string is a valid IPv6 address.
     """
     try:
-        ipaddress.IPv6Address(ip_str)
+        _ipv6_address_from_str(ip_str)
     except ValueError:
         return False
     return True

@@ -719,15 +719,15 @@ For each field, we describe the default widget used if you don't specify
     * Empty value: ``''`` (an empty string)
     * Normalizes to: A string. IPv6 addresses are normalized as described below.
     * Validates that the given value is a valid IP address.
-    * Error message keys: ``required``, ``invalid``
+    * Error message keys: ``required``, ``invalid``, ``max_length``
 
     The IPv6 address normalization follows :rfc:`4291#section-2.2` section 2.2,
     including using the IPv4 format suggested in paragraph 3 of that section, like
     ``::ffff:192.0.2.0``. For example, ``2001:0::0:01`` would be normalized to
     ``2001::1``, and ``::ffff:0a0a:0a0a`` to ``::ffff:10.10.10.10``. All characters
     are converted to lowercase.
 
-    Takes two optional arguments:
+    Takes three optional arguments:
 
     .. attribute:: protocol
 
@@ -742,6 +742,15 @@ For each field, we describe the default widget used if you don't specify
         ``192.0.2.1``. Default is disabled. Can only be used
         when ``protocol`` is set to ``'both'``.
 
+    .. attribute:: max_length
+
+        Defaults to 39, and behaves the same way as it does for
+        :class:`CharField`.
+
+    .. versionchanged:: 4.2.18
+
+        The default value for ``max_length`` was set to 39 characters.
+
 ``ImageField``
 --------------
 

@@ -5,3 +5,15 @@ Django 4.2.18 release notes
 *January 14, 2025*
 
 Django 4.2.18 fixes a security issue with severity "moderate" in 4.2.17.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -1,6 +1,7 @@
 from django.core.exceptions import ValidationError
 from django.forms import GenericIPAddressField
 from django.test import SimpleTestCase
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH
 
 
 class GenericIPAddressFieldTest(SimpleTestCase):
@@ -125,6 +126,35 @@ def test_generic_ipaddress_as_ipv6_only(self):
         ):
             f.clean("1:2")
 
+    def test_generic_ipaddress_max_length_custom(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+        f = GenericIPAddressField(max_length=len(addr))
+        f.clean(addr)
+
+    def test_generic_ipaddress_max_length_validation_error(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+
+        cases = [
+            ({}, MAX_IPV6_ADDRESS_LENGTH),  # Default value.
+            ({"max_length": len(addr) - 1}, len(addr) - 1),
+        ]
+        for kwargs, max_length in cases:
+            max_length_plus_one = max_length + 1
+            msg = (
+                f"Ensure this value has at most {max_length} characters (it has "
+                f"{max_length_plus_one}).'"
+            )
+            with self.subTest(max_length=max_length):
+                f = GenericIPAddressField(**kwargs)
+                with self.assertRaisesMessage(ValidationError, msg):
+                    f.clean("x" * max_length_plus_one)
+                with self.assertRaisesMessage(
+                    ValidationError, "This is not a valid IPv6 address."
+                ):
+                    f.clean(addr)
+
     def test_generic_ipaddress_as_generic_not_required(self):
         f = GenericIPAddressField(required=False)
         self.assertEqual(f.clean(""), "")
@@ -150,7 +180,8 @@ def test_generic_ipaddress_as_generic_not_required(self):
             f.clean(" fe80::223:6cff:fe8a:2e8a "), "fe80::223:6cff:fe8a:2e8a"
         )
         self.assertEqual(
-            f.clean(" 2a02::223:6cff:fe8a:2e8a "), "2a02::223:6cff:fe8a:2e8a"
+            f.clean(" " * MAX_IPV6_ADDRESS_LENGTH + " 2a02::223:6cff:fe8a:2e8a "),
+            "2a02::223:6cff:fe8a:2e8a",
         )
         with self.assertRaisesMessage(
             ValidationError, "'This is not a valid IPv6 address.'"

@@ -1,9 +1,17 @@
-import unittest
+import traceback
+from io import StringIO
 
-from django.utils.ipv6 import clean_ipv6_address, is_valid_ipv6_address
+from django.core.exceptions import ValidationError
+from django.test import SimpleTestCase
+from django.utils.ipv6 import (
+    MAX_IPV6_ADDRESS_LENGTH,
+    clean_ipv6_address,
+    is_valid_ipv6_address,
+)
+from django.utils.version import PY310
 
 
-class TestUtilsIPv6(unittest.TestCase):
+class TestUtilsIPv6(SimpleTestCase):
     def test_validates_correct_plain_address(self):
         self.assertTrue(is_valid_ipv6_address("fe80::223:6cff:fe8a:2e8a"))
         self.assertTrue(is_valid_ipv6_address("2a02::223:6cff:fe8a:2e8a"))
@@ -64,3 +72,29 @@ def test_unpacks_ipv4(self):
         self.assertEqual(
             clean_ipv6_address("::ffff:18.52.18.52", unpack_ipv4=True), "18.52.18.52"
         )
+
+    def test_address_too_long(self):
+        addresses = [
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228",  # IPv4-mapped IPv6 address
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228%123456",  # % scope/zone
+            "fe80::223:6cff:fe8a:2e8a:1234:5678:00000",  # MAX_IPV6_ADDRESS_LENGTH + 1
+        ]
+        msg = "This is the error message."
+        value_error_msg = "Unable to convert %s to an IPv6 address (value too long)."
+        for addr in addresses:
+            with self.subTest(addr=addr):
+                self.assertGreater(len(addr), MAX_IPV6_ADDRESS_LENGTH)
+                self.assertEqual(is_valid_ipv6_address(addr), False)
+                with self.assertRaisesMessage(ValidationError, msg) as ctx:
+                    clean_ipv6_address(addr, error_message=msg)
+                exception_traceback = StringIO()
+                if PY310:
+                    traceback.print_exception(ctx.exception, file=exception_traceback)
+                else:
+                    traceback.print_exception(
+                        type(ctx.exception),
+                        value=ctx.exception,
+                        tb=ctx.exception.__traceback__,
+                        file=exception_traceback,
+                    )
+                self.assertIn(value_error_msg % addr, exception_traceback.getvalue())

@@ -32,7 +32,7 @@
 )
 from django.utils.duration import duration_microseconds, duration_string
 from django.utils.functional import Promise, cached_property
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.text import capfirst
 from django.utils.translation import gettext_lazy as _
 
@@ -2233,7 +2233,7 @@ def __init__(
         self.default_validators = validators.ip_address_validators(
             protocol, unpack_ipv4
         )
-        kwargs["max_length"] = 39
+        kwargs["max_length"] = MAX_IPV6_ADDRESS_LENGTH
         super().__init__(verbose_name, name, *args, **kwargs)
 
     def check(self, **kwargs):
@@ -2260,7 +2260,7 @@ def deconstruct(self):
             kwargs["unpack_ipv4"] = self.unpack_ipv4
         if self.protocol != "both":
             kwargs["protocol"] = self.protocol
-        if kwargs.get("max_length") == 39:
+        if kwargs.get("max_length") == self.max_length:
             del kwargs["max_length"]
         return name, path, args, kwargs
 

@@ -46,7 +46,7 @@
 from django.utils.dateparse import parse_datetime, parse_duration
 from django.utils.deprecation import RemovedInDjango60Warning
 from django.utils.duration import duration_string
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.regex_helper import _lazy_re_compile
 from django.utils.translation import gettext_lazy as _
 from django.utils.translation import ngettext_lazy
@@ -1303,14 +1303,17 @@ def __init__(self, *, protocol="both", unpack_ipv4=False, **kwargs):
         self.default_validators = validators.ip_address_validators(
             protocol, unpack_ipv4
         )
+        kwargs.setdefault("max_length", MAX_IPV6_ADDRESS_LENGTH)
         super().__init__(**kwargs)
 
     def to_python(self, value):
         if value in self.empty_values:
             return ""
         value = value.strip()
         if value and ":" in value:
-            return clean_ipv6_address(value, self.unpack_ipv4)
+            return clean_ipv6_address(
+                value, self.unpack_ipv4, max_length=self.max_length
+            )
         return value
 
 

@@ -3,9 +3,22 @@
 from django.core.exceptions import ValidationError
 from django.utils.translation import gettext_lazy as _
 
+MAX_IPV6_ADDRESS_LENGTH = 39
+
+
+def _ipv6_address_from_str(ip_str, max_length=MAX_IPV6_ADDRESS_LENGTH):
+    if len(ip_str) > max_length:
+        raise ValueError(
+            f"Unable to convert {ip_str} to an IPv6 address (value too long)."
+        )
+    return ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+
 
 def clean_ipv6_address(
-    ip_str, unpack_ipv4=False, error_message=_("This is not a valid IPv6 address.")
+    ip_str,
+    unpack_ipv4=False,
+    error_message=_("This is not a valid IPv6 address."),
+    max_length=MAX_IPV6_ADDRESS_LENGTH,
 ):
     """
     Clean an IPv6 address string.
@@ -24,7 +37,7 @@ def clean_ipv6_address(
     Return a compressed IPv6 address or the same value.
     """
     try:
-        addr = ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+        addr = _ipv6_address_from_str(ip_str, max_length)
     except ValueError:
         raise ValidationError(
             error_message, code="invalid", params={"protocol": _("IPv6")}
@@ -43,7 +56,7 @@ def is_valid_ipv6_address(ip_str):
     Return whether or not the `ip_str` string is a valid IPv6 address.
     """
     try:
-        ipaddress.IPv6Address(ip_str)
+        _ipv6_address_from_str(ip_str)
     except ValueError:
         return False
     return True

@@ -761,15 +761,15 @@ For each field, we describe the default widget used if you don't specify
     * Empty value: ``''`` (an empty string)
     * Normalizes to: A string. IPv6 addresses are normalized as described below.
     * Validates that the given value is a valid IP address.
-    * Error message keys: ``required``, ``invalid``
+    * Error message keys: ``required``, ``invalid``, ``max_length``
 
     The IPv6 address normalization follows :rfc:`4291#section-2.2` section 2.2,
     including using the IPv4 format suggested in paragraph 3 of that section, like
     ``::ffff:192.0.2.0``. For example, ``2001:0::0:01`` would be normalized to
     ``2001::1``, and ``::ffff:0a0a:0a0a`` to ``::ffff:10.10.10.10``. All characters
     are converted to lowercase.
 
-    Takes two optional arguments:
+    Takes three optional arguments:
 
     .. attribute:: protocol
 
@@ -784,6 +784,15 @@ For each field, we describe the default widget used if you don't specify
         ``192.0.2.1``. Default is disabled. Can only be used
         when ``protocol`` is set to ``'both'``.
 
+    .. attribute:: max_length
+
+        Defaults to 39, and behaves the same way as it does for
+        :class:`CharField`.
+
+    .. versionchanged:: 4.2.18
+
+        The default value for ``max_length`` was set to 39 characters.
+
 ``ImageField``
 --------------
 

@@ -5,3 +5,15 @@ Django 4.2.18 release notes
 *January 14, 2025*
 
 Django 4.2.18 fixes a security issue with severity "moderate" in 4.2.17.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -5,3 +5,15 @@ Django 5.0.11 release notes
 *January 14, 2025*
 
 Django 5.0.11 fixes a security issue with severity "moderate" in 5.0.10.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -7,6 +7,18 @@ Django 5.1.5 release notes
 Django 5.1.5 fixes a security issue with severity "moderate" and one bug in
 5.1.4.
 
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.
+
 Bugfixes
 ========
 

@@ -1,6 +1,7 @@
 from django.core.exceptions import ValidationError
 from django.forms import GenericIPAddressField
 from django.test import SimpleTestCase
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH
 
 
 class GenericIPAddressFieldTest(SimpleTestCase):
@@ -125,6 +126,35 @@ def test_generic_ipaddress_as_ipv6_only(self):
         ):
             f.clean("1:2")
 
+    def test_generic_ipaddress_max_length_custom(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+        f = GenericIPAddressField(max_length=len(addr))
+        f.clean(addr)
+
+    def test_generic_ipaddress_max_length_validation_error(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+
+        cases = [
+            ({}, MAX_IPV6_ADDRESS_LENGTH),  # Default value.
+            ({"max_length": len(addr) - 1}, len(addr) - 1),
+        ]
+        for kwargs, max_length in cases:
+            max_length_plus_one = max_length + 1
+            msg = (
+                f"Ensure this value has at most {max_length} characters (it has "
+                f"{max_length_plus_one}).'"
+            )
+            with self.subTest(max_length=max_length):
+                f = GenericIPAddressField(**kwargs)
+                with self.assertRaisesMessage(ValidationError, msg):
+                    f.clean("x" * max_length_plus_one)
+                with self.assertRaisesMessage(
+                    ValidationError, "This is not a valid IPv6 address."
+                ):
+                    f.clean(addr)
+
     def test_generic_ipaddress_as_generic_not_required(self):
         f = GenericIPAddressField(required=False)
         self.assertEqual(f.clean(""), "")
@@ -150,7 +180,8 @@ def test_generic_ipaddress_as_generic_not_required(self):
             f.clean(" fe80::223:6cff:fe8a:2e8a "), "fe80::223:6cff:fe8a:2e8a"
         )
         self.assertEqual(
-            f.clean(" 2a02::223:6cff:fe8a:2e8a "), "2a02::223:6cff:fe8a:2e8a"
+            f.clean(" " * MAX_IPV6_ADDRESS_LENGTH + " 2a02::223:6cff:fe8a:2e8a "),
+            "2a02::223:6cff:fe8a:2e8a",
         )
         with self.assertRaisesMessage(
             ValidationError, "'This is not a valid IPv6 address.'"

@@ -1,9 +1,16 @@
-import unittest
+import traceback
+from io import StringIO
 
-from django.utils.ipv6 import clean_ipv6_address, is_valid_ipv6_address
+from django.core.exceptions import ValidationError
+from django.test import SimpleTestCase
+from django.utils.ipv6 import (
+    MAX_IPV6_ADDRESS_LENGTH,
+    clean_ipv6_address,
+    is_valid_ipv6_address,
+)
 
 
-class TestUtilsIPv6(unittest.TestCase):
+class TestUtilsIPv6(SimpleTestCase):
     def test_validates_correct_plain_address(self):
         self.assertTrue(is_valid_ipv6_address("fe80::223:6cff:fe8a:2e8a"))
         self.assertTrue(is_valid_ipv6_address("2a02::223:6cff:fe8a:2e8a"))
@@ -64,3 +71,21 @@ def test_unpacks_ipv4(self):
         self.assertEqual(
             clean_ipv6_address("::ffff:18.52.18.52", unpack_ipv4=True), "18.52.18.52"
         )
+
+    def test_address_too_long(self):
+        addresses = [
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228",  # IPv4-mapped IPv6 address
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228%123456",  # % scope/zone
+            "fe80::223:6cff:fe8a:2e8a:1234:5678:00000",  # MAX_IPV6_ADDRESS_LENGTH + 1
+        ]
+        msg = "This is the error message."
+        value_error_msg = "Unable to convert %s to an IPv6 address (value too long)."
+        for addr in addresses:
+            with self.subTest(addr=addr):
+                self.assertGreater(len(addr), MAX_IPV6_ADDRESS_LENGTH)
+                self.assertEqual(is_valid_ipv6_address(addr), False)
+                with self.assertRaisesMessage(ValidationError, msg) as ctx:
+                    clean_ipv6_address(addr, error_message=msg)
+                exception_traceback = StringIO()
+                traceback.print_exception(ctx.exception, file=exception_traceback)
+                self.assertIn(value_error_msg % addr, exception_traceback.getvalue())

@@ -32,7 +32,7 @@
 )
 from django.utils.duration import duration_microseconds, duration_string
 from django.utils.functional import Promise, cached_property
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.text import capfirst
 from django.utils.translation import gettext_lazy as _
 
@@ -2228,7 +2228,7 @@ def __init__(
         self.default_validators = validators.ip_address_validators(
             protocol, unpack_ipv4
         )
-        kwargs["max_length"] = 39
+        kwargs["max_length"] = MAX_IPV6_ADDRESS_LENGTH
         super().__init__(verbose_name, name, *args, **kwargs)
 
     def check(self, **kwargs):
@@ -2255,7 +2255,7 @@ def deconstruct(self):
             kwargs["unpack_ipv4"] = self.unpack_ipv4
         if self.protocol != "both":
             kwargs["protocol"] = self.protocol
-        if kwargs.get("max_length") == 39:
+        if kwargs.get("max_length") == self.max_length:
             del kwargs["max_length"]
         return name, path, args, kwargs
 

@@ -46,7 +46,7 @@
 from django.utils.dateparse import parse_datetime, parse_duration
 from django.utils.deprecation import RemovedInDjango60Warning
 from django.utils.duration import duration_string
-from django.utils.ipv6 import clean_ipv6_address
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH, clean_ipv6_address
 from django.utils.regex_helper import _lazy_re_compile
 from django.utils.translation import gettext_lazy as _
 from django.utils.translation import ngettext_lazy
@@ -1303,14 +1303,17 @@ def __init__(self, *, protocol="both", unpack_ipv4=False, **kwargs):
         self.default_validators = validators.ip_address_validators(
             protocol, unpack_ipv4
         )
+        kwargs.setdefault("max_length", MAX_IPV6_ADDRESS_LENGTH)
         super().__init__(**kwargs)
 
     def to_python(self, value):
         if value in self.empty_values:
             return ""
         value = value.strip()
         if value and ":" in value:
-            return clean_ipv6_address(value, self.unpack_ipv4)
+            return clean_ipv6_address(
+                value, self.unpack_ipv4, max_length=self.max_length
+            )
         return value
 
 

@@ -3,9 +3,22 @@
 from django.core.exceptions import ValidationError
 from django.utils.translation import gettext_lazy as _
 
+MAX_IPV6_ADDRESS_LENGTH = 39
+
+
+def _ipv6_address_from_str(ip_str, max_length=MAX_IPV6_ADDRESS_LENGTH):
+    if len(ip_str) > max_length:
+        raise ValueError(
+            f"Unable to convert {ip_str} to an IPv6 address (value too long)."
+        )
+    return ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+
 
 def clean_ipv6_address(
-    ip_str, unpack_ipv4=False, error_message=_("This is not a valid IPv6 address.")
+    ip_str,
+    unpack_ipv4=False,
+    error_message=_("This is not a valid IPv6 address."),
+    max_length=MAX_IPV6_ADDRESS_LENGTH,
 ):
     """
     Clean an IPv6 address string.
@@ -24,7 +37,7 @@ def clean_ipv6_address(
     Return a compressed IPv6 address or the same value.
     """
     try:
-        addr = ipaddress.IPv6Address(int(ipaddress.IPv6Address(ip_str)))
+        addr = _ipv6_address_from_str(ip_str, max_length)
     except ValueError:
         raise ValidationError(
             error_message, code="invalid", params={"protocol": _("IPv6")}
@@ -43,7 +56,7 @@ def is_valid_ipv6_address(ip_str):
     Return whether or not the `ip_str` string is a valid IPv6 address.
     """
     try:
-        ipaddress.IPv6Address(ip_str)
+        _ipv6_address_from_str(ip_str)
     except ValueError:
         return False
     return True

@@ -773,15 +773,15 @@ For each field, we describe the default widget used if you don't specify
     * Empty value: ``''`` (an empty string)
     * Normalizes to: A string. IPv6 addresses are normalized as described below.
     * Validates that the given value is a valid IP address.
-    * Error message keys: ``required``, ``invalid``
+    * Error message keys: ``required``, ``invalid``, ``max_length``
 
     The IPv6 address normalization follows :rfc:`4291#section-2.2` section 2.2,
     including using the IPv4 format suggested in paragraph 3 of that section, like
     ``::ffff:192.0.2.0``. For example, ``2001:0::0:01`` would be normalized to
     ``2001::1``, and ``::ffff:0a0a:0a0a`` to ``::ffff:10.10.10.10``. All characters
     are converted to lowercase.
 
-    Takes two optional arguments:
+    Takes three optional arguments:
 
     .. attribute:: protocol
 
@@ -796,6 +796,15 @@ For each field, we describe the default widget used if you don't specify
         ``192.0.2.1``. Default is disabled. Can only be used
         when ``protocol`` is set to ``'both'``.
 
+    .. attribute:: max_length
+
+        Defaults to 39, and behaves the same way as it does for
+        :class:`CharField`.
+
+    .. versionchanged:: 4.2.18
+
+        The default value for ``max_length`` was set to 39 characters.
+
 ``ImageField``
 --------------
 

@@ -5,3 +5,15 @@ Django 4.2.18 release notes
 *January 14, 2025*
 
 Django 4.2.18 fixes a security issue with severity "moderate" in 4.2.17.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -5,3 +5,15 @@ Django 5.0.11 release notes
 *January 14, 2025*
 
 Django 5.0.11 fixes a security issue with severity "moderate" in 5.0.10.
+
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.

@@ -7,6 +7,18 @@ Django 5.1.5 release notes
 Django 5.1.5 fixes a security issue with severity "moderate" and one bug in
 5.1.4.
 
+CVE-2024-56374: Potential denial-of-service vulnerability in IPv6 validation
+============================================================================
+
+Lack of upper bound limit enforcement in strings passed when performing IPv6
+validation could lead to a potential denial-of-service attack. The undocumented
+and private functions ``clean_ipv6_address`` and ``is_valid_ipv6_address`` were
+vulnerable, as was the  :class:`django.forms.GenericIPAddressField` form field,
+which has now been updated to define a ``max_length`` of 39 characters.
+
+The :class:`django.db.models.GenericIPAddressField` model field was not
+affected.
+
 Bugfixes
 ========
 

@@ -1,6 +1,7 @@
 from django.core.exceptions import ValidationError
 from django.forms import GenericIPAddressField
 from django.test import SimpleTestCase
+from django.utils.ipv6 import MAX_IPV6_ADDRESS_LENGTH
 
 
 class GenericIPAddressFieldTest(SimpleTestCase):
@@ -125,6 +126,35 @@ def test_generic_ipaddress_as_ipv6_only(self):
         ):
             f.clean("1:2")
 
+    def test_generic_ipaddress_max_length_custom(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+        f = GenericIPAddressField(max_length=len(addr))
+        f.clean(addr)
+
+    def test_generic_ipaddress_max_length_validation_error(self):
+        # Valid IPv4-mapped IPv6 address, len 45.
+        addr = "0000:0000:0000:0000:0000:ffff:192.168.100.228"
+
+        cases = [
+            ({}, MAX_IPV6_ADDRESS_LENGTH),  # Default value.
+            ({"max_length": len(addr) - 1}, len(addr) - 1),
+        ]
+        for kwargs, max_length in cases:
+            max_length_plus_one = max_length + 1
+            msg = (
+                f"Ensure this value has at most {max_length} characters (it has "
+                f"{max_length_plus_one}).'"
+            )
+            with self.subTest(max_length=max_length):
+                f = GenericIPAddressField(**kwargs)
+                with self.assertRaisesMessage(ValidationError, msg):
+                    f.clean("x" * max_length_plus_one)
+                with self.assertRaisesMessage(
+                    ValidationError, "This is not a valid IPv6 address."
+                ):
+                    f.clean(addr)
+
     def test_generic_ipaddress_as_generic_not_required(self):
         f = GenericIPAddressField(required=False)
         self.assertEqual(f.clean(""), "")
@@ -150,7 +180,8 @@ def test_generic_ipaddress_as_generic_not_required(self):
             f.clean(" fe80::223:6cff:fe8a:2e8a "), "fe80::223:6cff:fe8a:2e8a"
         )
         self.assertEqual(
-            f.clean(" 2a02::223:6cff:fe8a:2e8a "), "2a02::223:6cff:fe8a:2e8a"
+            f.clean(" " * MAX_IPV6_ADDRESS_LENGTH + " 2a02::223:6cff:fe8a:2e8a "),
+            "2a02::223:6cff:fe8a:2e8a",
         )
         with self.assertRaisesMessage(
             ValidationError, "'This is not a valid IPv6 address.'"

@@ -1,9 +1,16 @@
-import unittest
+import traceback
+from io import StringIO
 
-from django.utils.ipv6 import clean_ipv6_address, is_valid_ipv6_address
+from django.core.exceptions import ValidationError
+from django.test import SimpleTestCase
+from django.utils.ipv6 import (
+    MAX_IPV6_ADDRESS_LENGTH,
+    clean_ipv6_address,
+    is_valid_ipv6_address,
+)
 
 
-class TestUtilsIPv6(unittest.TestCase):
+class TestUtilsIPv6(SimpleTestCase):
     def test_validates_correct_plain_address(self):
         self.assertTrue(is_valid_ipv6_address("fe80::223:6cff:fe8a:2e8a"))
         self.assertTrue(is_valid_ipv6_address("2a02::223:6cff:fe8a:2e8a"))
@@ -64,3 +71,21 @@ def test_unpacks_ipv4(self):
         self.assertEqual(
             clean_ipv6_address("::ffff:18.52.18.52", unpack_ipv4=True), "18.52.18.52"
         )
+
+    def test_address_too_long(self):
+        addresses = [
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228",  # IPv4-mapped IPv6 address
+            "0000:0000:0000:0000:0000:ffff:192.168.100.228%123456",  # % scope/zone
+            "fe80::223:6cff:fe8a:2e8a:1234:5678:00000",  # MAX_IPV6_ADDRESS_LENGTH + 1
+        ]
+        msg = "This is the error message."
+        value_error_msg = "Unable to convert %s to an IPv6 address (value too long)."
+        for addr in addresses:
+            with self.subTest(addr=addr):
+                self.assertGreater(len(addr), MAX_IPV6_ADDRESS_LENGTH)
+                self.assertEqual(is_valid_ipv6_address(addr), False)
+                with self.assertRaisesMessage(ValidationError, msg) as ctx:
+                    clean_ipv6_address(addr, error_message=msg)
+                exception_traceback = StringIO()
+                traceback.print_exception(ctx.exception, file=exception_traceback)
+                self.assertIn(value_error_msg % addr, exception_traceback.getvalue())