A critical use-after-free vulnerability, dubbed as CVE-2023-33657, was recently discovered in NanoMQ .17.2, which is an embedded message queuing software designed for IoT and Edge computing applications. The vulnerability lies in the improper handling of data tracing within the software and can be exploited by an attacker to cause a denial of service attack. This long-read post will delve into the details of the vulnerability, the affected code snippets, and the potential exploitation of this security issue.


The vulnerability in question exists within the nni_mqtt_msg_get_publish_property() function in the mqtt_msg.c file. The issue here stems from improper data tracing, where, due to faulty memory management, the data can be accessed and manipulated even after it has been marked for deletion or termed as 'free.' In such cases, an attacker can exploit this vulnerability to crash the application and initiate a denial-of-service attack.

Code Snippet

The vulnerable code snippet in the mqtt_msg.c file, specifically in the nni_mqtt_msg_get_publish_property() function, is as follows:

nni_msg *msg;
struct nni_mqtt_message_publish *publish;

publish = GET_TAG_VALUE(*property);
if (publish != NULL) { numel--; }

In the above code snippet, the value of publish, which is a pointer to the nni_mqtt_message_publish structure, is retrieved from the property variable using the GET_TAG_VALUE macro. The problem occurs when publish is not properly traced and still has access to the memory even if it was marked as 'free' after being accessed.

Exploitation Details

An attacker can exploit this vulnerability by carefully crafting an MQTT message with malicious payload values. In this exploitation scenario, the attacker can cause a corruption in the application's memory, which would lead to a crash, ultimately rendering the NanoMQ service unresponsive or causing a denial-of-service attack.

Original References

This vulnerability has been reported and documented by security researchers and can be found in the following sources:

1. CVE-2023-33657 - NVD Detail
2. Github Issue - NanoMQ-.17.2 Use-After-Free Vulnerability
3. MitRE - CVE Entry

Mitigation and Recommendations

As of now, there is no official patch available to fix this vulnerability. However, the following preventive measures are recommended:

1. To minimize the risk of exploitation, it is suggested to restrict access to the service based on IP whitelisting or using a firewall to allow only trusted sources.
2. Keep monitoring and applying security updates released by the NanoMQ developers and promptly install patches when they become available.


The discovery of the use-after-free vulnerability in NanoMQ .17.2, CVE-2023-33657, emphasizes the importance of secure memory and data management in applications, especially those deployed in IoT and Edge computing environments. Currently, no official patch has been released to address this issue; however, steps can be taken to mitigate the risk of exploitation by implementing proper access control measures and staying updated with the latest security patches released by the software developers.


Published on: 06/08/2023 13:15:00 UTC
Last modified on: 06/14/2023 17:25:00 UTC