From dda265f85409cc527c6f8f22b43640dce50c8d9f Mon Sep 17 00:00:00 2001
From: liooooo29 <1741196223@qq.com>
Date: Mon, 10 Aug 2026 15:43:26 +0800
Subject: [PATCH] fix: send Malformed Packet CONNACK for username parse error
 in MQTT 5.0

---
 src/handle_connect.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/handle_connect.c b/src/handle_connect.c
index 4bbc66eec0..280356112e 100644
--- a/src/handle_connect.c
+++ b/src/handle_connect.c
@@ -809,6 +809,9 @@ static int read_and_verify_client_credentials_from_packet(struct mosquitto *cont
 	if(username_flag){
 		rc = set_username_from_packet(context, username, clientid);
 		if(rc != MOSQ_ERR_SUCCESS){
+			if(context->protocol == mosq_p_mqtt5){
+				send__connack(context, 0, MQTT_RC_MALFORMED_PACKET, NULL);
+			}
 			return rc;
 		}
 	}else{