Fix thread-safety issue with shared BinaryMessage in concurrent sessions

 - Duplicate ByteBuffer before sending to avoid position conflicts
 - Ensure thread-safe handling of binary messages across multiple sessions

Author: xeromank

spring-websocket/src/main/java/org/springframework/web/socket/handler/ConcurrentWebSocketSessionDecorator.java

@@ -17,6 +17,7 @@
 package org.springframework.web.socket.handler;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.util.Queue;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -28,6 +29,7 @@
 import org.apache.commons.logging.LogFactory;
 import org.jspecify.annotations.Nullable;
 
+import org.springframework.web.socket.BinaryMessage;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.WebSocketMessage;
 import org.springframework.web.socket.WebSocketSession;
@@ -194,7 +196,7 @@ private boolean tryFlushMessageBuffer() throws IOException {
 					}
 					this.bufferSize.addAndGet(-message.getPayloadLength());
 					this.sendStartTime = System.currentTimeMillis();
-					getDelegate().sendMessage(message);
+					getDelegate().sendMessage(prepareMessage(message));
 					this.sendStartTime = 0;
 				}
 			}
@@ -207,6 +209,14 @@ private boolean tryFlushMessageBuffer() throws IOException {
 		return false;
 	}
 
+	private WebSocketMessage<?> prepareMessage(WebSocketMessage<?> message) {
+		if (message instanceof BinaryMessage) {
+			ByteBuffer payload = ((BinaryMessage) message).getPayload();
+			return new BinaryMessage(payload.duplicate(), message.isLast());
+		}
+		return message;
+	}
+
 	private void checkSessionLimits() {
 		if (!shouldNotSend() && this.closeLock.tryLock()) {
 			try {