From 0691935ed9d45fb14713d20c1e5421b326383d2c Mon Sep 17 00:00:00 2001
From: "Roger A. Light" <roger@atchoo.org>
Date: Thu, 31 Oct 2024 23:06:48 +0000
Subject: [PATCH] Fix RESERVED packets not being quickly rejected.

Closes #2325
---
 ChangeLog.txt           | 4 ++++
 include/mqtt_protocol.h | 1 +
 lib/packet_mosq.c       | 5 +++++
 3 files changed, 10 insertions(+)

diff --git a/ChangeLog.txt b/ChangeLog.txt
index 0b706d90bd..1f235b6701 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -1,6 +1,10 @@
 2.0.21 - 2024-xx-xx
 ===================
 
+Broker:
+- Fix clients sending a RESERVED packet not being quickly disconnected.
+  Closes #2325.
+
 Client library:
 - Fix threads linking on Windows for static libmosquitto library
   Closes #3143
diff --git a/include/mqtt_protocol.h b/include/mqtt_protocol.h
index ac86787739..ef05379d3f 100644
--- a/include/mqtt_protocol.h
+++ b/include/mqtt_protocol.h
@@ -34,6 +34,7 @@ SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 
 
 /* Message types */
+#define CMD_RESERVED 0x00U
 #define CMD_CONNECT 0x10U
 #define CMD_CONNACK 0x20U
 #define CMD_PUBLISH 0x30U
diff --git a/lib/packet_mosq.c b/lib/packet_mosq.c
index b063eb718e..2ea41b0e8e 100644
--- a/lib/packet_mosq.c
+++ b/lib/packet_mosq.c
@@ -395,6 +395,11 @@ int packet__read(struct mosquitto *mosq)
 			/* Clients must send CONNECT as their first command. */
 			if(!(mosq->bridge) && state == mosq_cs_new && (byte&0xF0) != CMD_CONNECT){
 				return MOSQ_ERR_PROTOCOL;
+			}else if((byte&0xF0) == CMD_RESERVED){
+				if(mosq->protocol == mosq_p_mqtt5){
+					send__disconnect(mosq, MQTT_RC_PROTOCOL_ERROR, NULL);
+				}
+				return MOSQ_ERR_PROTOCOL;
 			}
 #endif
 		}else{