A heap buffer overflow vulnerability (CVE-2023-33660) has been discovered in NanoMQ, an open-source, lightweight message broker that utilizes MQTT protocol for communication. This vulnerability exists in version .17.2 of the software and can lead to potential denial of service (DoS) attacks on affected systems. This post provides an in-depth analysis of the vulnerability, including code snippets, original references, and details on how the exploit works.

Vulnerability Description

The vulnerability is caused by a flaw in the copyn_str() function, which resides in the mqtt_parser.c file. An attacker can exploit this vulnerability to cause a DoS attack by crafting a malicious MQTT message, resulting in a crash of the NanoMQ service.

Code Snippet

void copyn_str(u_char **dest, const u_char *src, size_t n) {
  *dest = (u_char *)malloc(n + 1);
  memcpy(*dest, src, n);
  (*dest)[n] = '\';
}

This function takes three parameters: a pointer to a destination buffer, a pointer to a source buffer, and the number of characters to copy. The function fails to properly check if there is enough space in the destination buffer before copying the specified number of characters from the source buffer.

Exploit Details

The function copyn_str() can be triggered by an attacker through a specially crafted MQTT message that contains a large payload. When the NanoMQ service attempts to parse this message, it calls the copyn_str() function, which in turn causes the heap buffer overflow. This can lead to a crash in the NanoMQ service, effectively causing a DoS attack.

1. NanoMQ repository on Github
2. MQTT Parser File on Github
3. CVE-2023-33660 on NIST's National Vulnerability Database

Remediation Steps

Users are advised to upgrade to the latest version of NanoMQ, which includes patches to address this vulnerability. In addition, developers should follow secure coding practices when writing code, ensuring that there are proper checks for buffer sizes before copying data.

1. Upgrade to the latest version of NanoMQ
2. Implement secure coding practices, such as CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Conclusion

The heap buffer overflow vulnerability (CVE-2023-33660) in NanoMQ .17.2 is a prime example of the security issues that can arise from not properly validating buffer sizes before copying data. By understanding the details of this exploit and implementing secure coding practices, developers can mitigate the risks associated with this vulnerability.

Timeline

Published on: 06/08/2023 12:15:00 UTC
Last modified on: 06/14/2023 17:45:00 UTC