mid == 0 is a protocol error.

lib/handle_pubackcomp.c

@@ -49,6 +49,7 @@ int handle__pubackcomp(struct mosquitto *mosq, const char *type)
 	assert(mosq);
 	rc = packet__read_uint16(&mosq->in_packet, &mid);
 	if(rc) return rc;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(mosq->protocol == mosq_p_mqtt5){
 		rc = property__read_all(PUBACK, &mosq->in_packet, &properties);

lib/handle_publish.c

@@ -67,6 +67,10 @@ int handle__publish(struct mosquitto *mosq)
 			message__cleanup(&message);
 			return rc;
 		}
+		if(mid == 0){
+			message__cleanup(&message);
+			return MOSQ_ERR_PROTOCOL;
+		}
 		message->msg.mid = (int)mid;
 	}
 

lib/handle_pubrec.c

@@ -44,6 +44,7 @@ int handle__pubrec(struct mosquitto *mosq)
 	assert(mosq);
 	rc = packet__read_uint16(&mosq->in_packet, &mid);
 	if(rc) return rc;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(mosq->protocol == mosq_p_mqtt5){
 		rc = property__read_all(PUBREC, &mosq->in_packet, &properties);

lib/handle_pubrel.c

@@ -53,6 +53,7 @@ int handle__pubrel(struct mosquitto_db *db, struct mosquitto *mosq)
 	}
 	rc = packet__read_uint16(&mosq->in_packet, &mid);
 	if(rc) return rc;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(mosq->protocol == mosq_p_mqtt5){
 		rc = property__read_all(PUBREL, &mosq->in_packet, &properties);

lib/handle_suback.c

@@ -49,6 +49,7 @@ int handle__suback(struct mosquitto *mosq)
 #endif
 	rc = packet__read_uint16(&mosq->in_packet, &mid);
 	if(rc) return rc;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(mosq->protocol == mosq_p_mqtt5){
 		rc = property__read_all(SUBACK, &mosq->in_packet, &properties);

lib/handle_unsuback.c

@@ -51,6 +51,7 @@ int handle__unsuback(struct mosquitto *mosq)
 #endif
 	rc = packet__read_uint16(&mosq->in_packet, &mid);
 	if(rc) return rc;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(mosq->protocol == mosq_p_mqtt5){
 		rc = property__read_all(UNSUBACK, &mosq->in_packet, &properties);

src/handle_publish.c

@@ -131,6 +131,10 @@ int handle__publish(struct mosquitto_db *db, struct mosquitto *context)
 			mosquitto__free(topic);
 			return 1;
 		}
+		if(mid == 0){
+			mosquitto__free(topic);
+			return MOSQ_ERR_PROTOCOL;
+		}
 	}
 
 	if(context->protocol == mosq_p_mqtt5){

src/handle_subscribe.c

@@ -50,6 +50,7 @@ int handle__subscribe(struct mosquitto_db *db, struct mosquitto *context)
 		}
 	}
 	if(packet__read_uint16(&context->in_packet, &mid)) return 1;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(context->protocol == mosq_p_mqtt5){
 		rc = property__read_all(SUBSCRIBE, &context->in_packet, &properties);

src/handle_unsubscribe.c

@@ -42,6 +42,7 @@ int handle__unsubscribe(struct mosquitto_db *db, struct mosquitto *context)
 		}
 	}
 	if(packet__read_uint16(&context->in_packet, &mid)) return 1;
+	if(mid == 0) return MOSQ_ERR_PROTOCOL;
 
 	if(context->protocol == mosq_p_mqtt5){
 		rc = property__read_all(UNSUBSCRIBE, &context->in_packet, &properties);