diff --git a/src/main/java/core/packetproxy/common/UDPSocketEndpoint.java b/src/main/java/core/packetproxy/common/UDPSocketEndpoint.java
index 8ec5efbe..63bab73b 100644
--- a/src/main/java/core/packetproxy/common/UDPSocketEndpoint.java
+++ b/src/main/java/core/packetproxy/common/UDPSocketEndpoint.java
@@ -33,6 +33,7 @@ public class UDPSocketEndpoint implements Endpoint {
 
 	public UDPSocketEndpoint(InetSocketAddress addr) throws Exception {
 		socket = new DatagramSocket();
+		socket.connect(addr);
 		serverAddr = addr;
 		pipe = new PipeEndpoint(addr);
 		loop();
diff --git a/src/test/java/packetproxy/common/UDPSocketEndpointTest.java b/src/test/java/packetproxy/common/UDPSocketEndpointTest.java
new file mode 100644
index 00000000..2fa6a78f
--- /dev/null
+++ b/src/test/java/packetproxy/common/UDPSocketEndpointTest.java
@@ -0,0 +1,182 @@
+/*
+ * Copyright 2026 DeNA Co., Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package packetproxy.common;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import org.junit.jupiter.api.Test;
+
+public class UDPSocketEndpointTest {
+
+	@Test
+	public void testIgnorePacketFromUnexpectedSource() throws Exception {
+		try (var fixture = openFixture()) {
+			var request = ascii("request");
+			var response = ascii("server-response");
+			var intruderPayload = ascii("intruder-payload");
+
+			fixture.sendRequestFromEndpoint(request);
+			var serverReceivedPacket = fixture.receiveFromEndpoint();
+			assertArrayEquals(request, getPayload(serverReceivedPacket));
+
+			var endpointResponse = fixture.readFromEndpointAsync();
+			fixture.sendUnexpectedPacket(intruderPayload);
+			assertReadTimeout(endpointResponse);
+
+			fixture.sendResponseToEndpoint(response, serverReceivedPacket);
+			assertArrayEquals(response, fixture.await(endpointResponse));
+		}
+	}
+
+	private TestFixture openFixture() throws Exception {
+		var existingThreads = new HashSet<>(Thread.getAllStackTraces().keySet());
+		var serverSocket = new DatagramSocket(new InetSocketAddress("127.0.0.1", 0));
+		serverSocket.setSoTimeout(1000);
+		var intruderSocket = new DatagramSocket(new InetSocketAddress("127.0.0.1", 0));
+		var endpoint = new UDPSocketEndpoint(new InetSocketAddress("127.0.0.1", serverSocket.getLocalPort()));
+		var endpointThreads = getNewThreads(existingThreads);
+		var executor = Executors.newSingleThreadExecutor();
+		return new TestFixture(serverSocket, intruderSocket, endpoint, endpointThreads, executor);
+	}
+
+	private byte[] ascii(String value) {
+		return value.getBytes(StandardCharsets.US_ASCII);
+	}
+
+	private byte[] getPayload(DatagramPacket packet) {
+		return Arrays.copyOf(packet.getData(), packet.getLength());
+	}
+
+	private void assertReadTimeout(Future<byte[]> future) {
+		assertThrows(TimeoutException.class, () -> future.get(200, TimeUnit.MILLISECONDS));
+	}
+
+	private Set<Thread> getNewThreads(Set<Thread> existingThreads) {
+		var currentThreads = Thread.getAllStackTraces().keySet();
+		var newThreads = new HashSet<Thread>();
+		for (var thread : currentThreads) {
+
+			if (!existingThreads.contains(thread)) {
+				newThreads.add(thread);
+			}
+		}
+		return newThreads;
+	}
+
+	private void closeEndpoint(UDPSocketEndpoint endpoint, Set<Thread> endpointThreads) throws Exception {
+		getSocket(endpoint).close();
+
+		var pipe = getPipe(endpoint);
+		pipe.getRawEndpoint().getInputStream().close();
+		pipe.getRawEndpoint().getOutputStream().close();
+		pipe.getProxyRawEndpoint().getInputStream().close();
+		pipe.getProxyRawEndpoint().getOutputStream().close();
+
+		for (var thread : endpointThreads) {
+
+			thread.interrupt();
+			thread.join(1000);
+		}
+	}
+
+	private DatagramSocket getSocket(UDPSocketEndpoint endpoint) throws Exception {
+		var socketField = UDPSocketEndpoint.class.getDeclaredField("socket");
+		socketField.setAccessible(true);
+		return (DatagramSocket) socketField.get(endpoint);
+	}
+
+	private PipeEndpoint getPipe(UDPSocketEndpoint endpoint) throws Exception {
+		var pipeField = UDPSocketEndpoint.class.getDeclaredField("pipe");
+		pipeField.setAccessible(true);
+		return (PipeEndpoint) pipeField.get(endpoint);
+	}
+
+	private class TestFixture implements AutoCloseable {
+
+		private static final int BUFFER_SIZE = 4096;
+		private final DatagramSocket serverSocket;
+		private final DatagramSocket intruderSocket;
+		private final UDPSocketEndpoint endpoint;
+		private final Set<Thread> endpointThreads;
+		private final ExecutorService executor;
+
+		private TestFixture(DatagramSocket serverSocket, DatagramSocket intruderSocket, UDPSocketEndpoint endpoint,
+				Set<Thread> endpointThreads, ExecutorService executor) {
+			this.serverSocket = serverSocket;
+			this.intruderSocket = intruderSocket;
+			this.endpoint = endpoint;
+			this.endpointThreads = endpointThreads;
+			this.executor = executor;
+		}
+
+		private void sendRequestFromEndpoint(byte[] payload) throws Exception {
+			var endpointOutput = endpoint.getOutputStream();
+			endpointOutput.write(payload);
+			endpointOutput.flush();
+		}
+
+		private DatagramPacket receiveFromEndpoint() throws Exception {
+			var packet = new DatagramPacket(new byte[BUFFER_SIZE], BUFFER_SIZE);
+			serverSocket.receive(packet);
+			return packet;
+		}
+
+		private Future<byte[]> readFromEndpointAsync() {
+			return executor.submit(() -> {
+				var endpointInput = endpoint.getInputStream();
+				var buf = new byte[BUFFER_SIZE];
+				var len = endpointInput.read(buf);
+				return Arrays.copyOf(buf, len);
+			});
+		}
+
+		private void sendUnexpectedPacket(byte[] payload) throws Exception {
+			var packet = new DatagramPacket(payload, payload.length,
+					new InetSocketAddress("127.0.0.1", endpoint.getLocalPort()));
+			intruderSocket.send(packet);
+		}
+
+		private void sendResponseToEndpoint(byte[] payload, DatagramPacket requestPacket) throws Exception {
+			var responsePacket = new DatagramPacket(payload, payload.length, requestPacket.getSocketAddress());
+			serverSocket.send(responsePacket);
+		}
+
+		private byte[] await(Future<byte[]> future) throws Exception {
+			return future.get(1, TimeUnit.SECONDS);
+		}
+
+		@Override
+		public void close() throws Exception {
+			executor.shutdownNow();
+			closeEndpoint(endpoint, endpointThreads);
+			intruderSocket.close();
+			serverSocket.close();
+		}
+	}
+}