From eecb7baaaa243facfe79940410e73d3d37d4ea7c Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith" <68491+gpshead@users.noreply.github.com>
Date: Sun, 1 Nov 2026 12:36:11 -0800
Subject: [PATCH] [3.15] gh-161100: Fix `IPv6Interface.is_unspecified` for
 IPv4-mapped addresses (GH-161101)

Defer to IPv6Address.is_unspecified, as the is_loopback override does,
so ::ffff:0.0.0.0/128 interfaces are unspecified like the address.

ANT-2026-DIFE27WF

(cherry picked from commit 6e6e83eb0da240e618806b3ded86e817dcaa4f18)
---
 Lib/ipaddress.py                              |  2 +-
 Lib/test/test_ipaddress.py                    | 19 +++++++++++++++++++
 ...-10-22-05-20-06.gh-issue-161100.pLgnlA.rst |  3 +++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-10-22-05-20-06.gh-issue-161100.pLgnlA.rst

diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 198dcd6de32a440..4c7b5b751d6d27f 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -2272,7 +2272,7 @@ def with_hostmask(self):
 
     @property
     def is_unspecified(self):
-        return self._ip == 0 and self.network.is_unspecified
+        return super().is_unspecified and self.network.is_unspecified
 
     @property
     def is_loopback(self):
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 8cb1e6549737cf2..595288a5cd62574 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -2447,6 +2447,14 @@ def testReservedIpv6(self):
         self.assertEqual(False, ipaddress.ip_network('::1').is_unspecified)
         self.assertEqual(False, ipaddress.ip_network('::/127').is_unspecified)
 
+        self.assertTrue(ipaddress.ip_interface('::/128').is_unspecified)
+        self.assertTrue(
+            ipaddress.ip_interface('::ffff:0.0.0.0/128').is_unspecified)
+        self.assertFalse(ipaddress.ip_interface('::/127').is_unspecified)
+        self.assertFalse(
+            ipaddress.ip_interface('::ffff:0.0.0.0/127').is_unspecified)
+        self.assertFalse(ipaddress.ip_interface('::1/128').is_unspecified)
+
         self.assertEqual(True,
                          ipaddress.ip_network('2001::1/128').is_private)
         self.assertEqual(True,
@@ -2536,6 +2544,17 @@ def testIpv4MappedProperties(self):
                 self.assertEqual(ipv4.is_link_local, ipv6.is_link_local)
                 self.assertEqual(ipv4.is_loopback, ipv6.is_loopback)
 
+                ipv4 = ipaddress.IPv4Interface(addr4)
+                ipv6 = ipaddress.IPv6Interface(f"::ffff:{addr4}")
+
+                self.assertEqual(ipv4.is_global, ipv6.is_global)
+                self.assertEqual(ipv4.is_private, ipv6.is_private)
+                self.assertEqual(ipv4.is_reserved, ipv6.is_reserved)
+                self.assertEqual(ipv4.is_multicast, ipv6.is_multicast)
+                self.assertEqual(ipv4.is_unspecified, ipv6.is_unspecified)
+                self.assertEqual(ipv4.is_link_local, ipv6.is_link_local)
+                self.assertEqual(ipv4.is_loopback, ipv6.is_loopback)
+
     def testIpv4MappedPrivateCheck(self):
         self.assertEqual(
                 True, ipaddress.ip_address('::ffff:192.168.1.1').is_private)
diff --git a/Misc/NEWS.d/next/Library/2026-10-22-05-20-06.gh-issue-161100.pLgnlA.rst b/Misc/NEWS.d/next/Library/2026-10-22-05-20-06.gh-issue-161100.pLgnlA.rst
new file mode 100644
index 000000000000000..b23de8a22ca9683
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-22-05-20-06.gh-issue-161100.pLgnlA.rst
@@ -0,0 +1,3 @@
+Fix :attr:`!ipaddress.IPv6Interface.is_unspecified` returning ``False`` for
+the IPv4-mapped address ``::ffff:0.0.0.0``.  It now gives the same result as
+:attr:`ipaddress.IPv6Address.is_unspecified`.