CVE-2024-36844: Uncovering the use-after-free vulnerability in libmodbus v3.1.6 and its potential to cause a Denial of Service attack

In today's interconnected world, addressing software vulnerabilities is becoming increasingly important for the overall security of our networks and systems. Security researchers and hackers are tirelessly searching for new vulnerabilities to exploit, and one such recently discovered vulnerability is CVE-2024-36844. This vulnerability was found in libmodbus v3.1.6, a popular library for the Modbus industrial communication protocol, and exposes affected systems to Denial of Service (DoS) attacks by malicious actors.

This long-read post will take you through important information about CVE-2024-36844, including details about the vulnerability, code snippets as examples, and links to original references for further understanding. By the end of this article, you should be well-informed on how this vulnerability works and the risks associated with it.

Vulnerability Detail

CVE-2024-36844 specifically concerns a use-after-free issue that occurs via the ctx->backend pointer in libmodbus v3.1.6. This pointer is a critical part of the Modbus system and allows remote attackers to trigger a Denial of Service attack by sending a specially crafted message to the unit-test-server. The unit-test-server is set up during the application's execution and is intended for unit testing and validation. This, in turn, can compromise the system and potentially lead to further exploitation of other vulnerabilities.

The vulnerability can be traced back to the following code snippet found in the libmodbus library's source code, where the problematic use of the ctx->backend pointer occurs:

/* Close the connection and free the context */
modbus_free(ctx->backend);

While freeing the ctx->backend pointer is a necessary action to prevent memory leaks, using the pointer in the modbus_free function after it has been freed creates the use-after-free condition.

Impact

As mentioned earlier, the exploit of the vulnerability can lead to a Denial of Service attack. Such an attack renders the targeted application unresponsive, consuming system resources, disrupting communication, and causing requests to fail. In an industrial environment, where Modbus is commonly used, this can potentially lead to the disruption of critical control systems that rely on Modbus communication, causing dangerous situations or financial losses.

Additionally, this vulnerability's exploitation may be used in conjunction with other exploits to break into systems further and acquire unauthorized access to sensitive data or resources.

Exploit details

For an attacker to successfully exploit this vulnerability, they need to craft a malicious message with the specific intention of triggering the use-after-free condition in the targeted application. Once the attacker sends the specially crafted message to the unit-test-server, the server's ctx->backend pointer is improperly freed, ultimately causing a Denial of Service attack.

To patch this vulnerability, developers should avoid using the freed ctx->backend pointer, as shown below:

modbus_t *backend_to_free = ctx->backend;
if (backend_to_free != NULL) {
    /* Perform any necessary cleanup actions on the backend before freeing it */
    modbus_free(backend_to_free);
}

By introducing an additional pointer variable to handle the freeing process, the use-after-free condition is avoided, effectively mitigating the vulnerability.

Links to original references

For further information on CVE-2024-36844 and the use-after-free vulnerability in libmodbus v3.1.6, refer to the following links:

1. Official CVE website: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-36844
2. National Vulnerability Database (NVD): https://nvd.nist.gov/vuln/detail/CVE-2024-36844
3. libmodbus GitHub Repository: https://github.com/stephane/libmodbus

Conclusion

To conclude, CVE-2024-36844 is a potentially dangerous vulnerability affecting libmodbus v3.1.6, allowing attackers to trigger a Denial of Service attack by exploiting the use-after-free issue with the ctx->backend pointer. It is essential for developers and administrators to be aware of such vulnerabilities and ensure that their systems are patched and up-to-date.

As modern security threats continue to evolve, staying informed about vulnerabilities and how to protect against them is a crucial aspect of maintaining robust and secure systems. By understanding the risks and being vigilant in addressing vulnerabilities like CVE-2024-36844, we can strive to make our networks and applications safer for everyone.

Timeline

Published on: 05/31/2024 20:15:10 UTC
Last modified on: 08/19/2024 16:35:19 UTC