python · gpshead · May 24, 2025 · Jan 14, 2025 · Jan 14, 2025 · Jan 14, 2025
diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
@@ -1661,7 +1661,11 @@ def _ip_int_from_string(cls, ip_str):
        if not ip_str:
            raise AddressValueError('Address cannot be empty')

-        parts = ip_str.split(':')
+        # We want to allow more parts than the max to be 'split'
+        # to preserve the correct error message when there are
+        # too many parts combined with '::'
+        _max_parts = cls._HEXTET_COUNT + 1
+        parts = ip_str.split(':', maxsplit=_max_parts)

        # An IPv6 address needs at least 2 colons (3 parts).
        _min_parts = 3
@@ -1681,7 +1685,6 @@ def _ip_int_from_string(cls, ip_str):
        # An IPv6 address can't have more than 8 colons (9 parts).
        # The extra colon comes from using the "::" notation for a single
        # leading or trailing zero part.
-        _max_parts = cls._HEXTET_COUNT + 1
        if len(parts) > _max_parts:
            msg = "At most %d colons permitted in %r" % (_max_parts-1, ip_str)
            raise AddressValueError(msg)

diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
@@ -396,6 +396,8 @@ def assertBadSplit(addr):
        assertBadSplit("8:7:6:5:4:3:2:1::%scope")
        # A trailing IPv4 address is two parts
        assertBadSplit("10:9:8:7:6:5:4:3:42.42.42.42%scope")
+        # Long IPv6 address
+        assertBadSplit(("0:" * 10000) + "0")

    def test_bad_address_split_v6_too_many_parts(self):
        def assertBadSplit(addr):

diff --git a/Misc/NEWS.d/next/Security/2025-01-14-11-19-07.gh-issue-128840.M1doZW.rst b/Misc/NEWS.d/next/Security/2025-01-14-11-19-07.gh-issue-128840.M1doZW.rst
@@ -0,0 +1,3 @@
+Limit the number of splitting on colons (``:``) that will occur while parsing
+an IPv6 address. This prevents excessive memory consumption and potential
+denial-of-service when parsing a large IPv6 address.
-Original file line number
+Diff line change
@@ -0,0 +1,3 @@
+    Limit the number of splitting on colons (``:``) that will occur while parsing
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+    an IPv6 address. This prevents excessive memory consumption and potential
+    denial-of-service when parsing a large IPv6 address.