From 98de2ad302ef2740bb8c65891df12ad0ba1f511b Mon Sep 17 00:00:00 2001
From: PHJ2000 <105151063+PHJ2000@users.noreply.github.com>
Date: Tue, 6 Oct 2026 00:44:33 +0900
Subject: [PATCH] Limit long-based Ethernet addresses to 48 bits

---
 .../com/fasterxml/uuid/EthernetAddress.java   |  2 +-
 .../fasterxml/uuid/EthernetAddressTest.java   | 24 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/main/java/com/fasterxml/uuid/EthernetAddress.java b/src/main/java/com/fasterxml/uuid/EthernetAddress.java
index f3222d5..27c51e0 100644
--- a/src/main/java/com/fasterxml/uuid/EthernetAddress.java
+++ b/src/main/java/com/fasterxml/uuid/EthernetAddress.java
@@ -169,7 +169,7 @@ public EthernetAddress(byte [] addr)
      *    bytes.
      */
     public EthernetAddress(long addr) {
-        _address = addr;
+        _address = addr & 0x0000ffffffffffffL;
     }
     
     /**
diff --git a/src/test/java/com/fasterxml/uuid/EthernetAddressTest.java b/src/test/java/com/fasterxml/uuid/EthernetAddressTest.java
index f3b4629..9921c92 100644
--- a/src/test/java/com/fasterxml/uuid/EthernetAddressTest.java
+++ b/src/test/java/com/fasterxml/uuid/EthernetAddressTest.java
@@ -1425,4 +1425,28 @@ private void assertEthernetAddressArraysAreNotEqual(byte[] array1,
         }
         fail("Array1 and Array2 matched");
     }
+
+    @Test
+    public void longConstructorUsesOnlyLowestSixBytes() {
+        long expected = 0x0123456789abL;
+        EthernetAddress canonical = new EthernetAddress(expected);
+        for (long highBits : new long[] { 0x0001000000000000L, Long.MIN_VALUE, 0xffff000000000000L }) {
+            EthernetAddress address = new EthernetAddress(highBits | expected);
+            assertEquals(expected, address.toLong());
+            assertEquals(canonical, address);
+            assertEquals(canonical.hashCode(), address.hashCode());
+            assertEquals(0, canonical.compareTo(address));
+            assertEquals(canonical.toString(), address.toString());
+            assertArrayEquals(canonical.toByteArray(), address.toByteArray());
+        }
+    }
+
+    @Test
+    public void longFactoryRoundTripsNegativeInput() {
+        EthernetAddress address = EthernetAddress.valueOf(-1L);
+        assertEquals(0xffffffffffffL, address.toLong());
+        assertEquals(address, new EthernetAddress(address.toString()));
+        assertEquals(address, new EthernetAddress(address.toByteArray()));
+    }
+
 }