A vulnerability has been discovered in certain modem devices (CVE-2022-33294) that can cause a temporary Denial of Service (DoS) situation. This occurs when the modem receives a response to a Lightweight Machine-to-Machine (LwM2M) registration/update/bootstrap request message, and a NULL pointer dereference error takes place. In this post, we will discuss the details of the exploit, review the code snippet responsible for the vulnerability, and provide links to original references.

Background

LwM2M is a communication protocol used for the management of IoT devices on various networks. It is designed to facilitate device and service management in a lightweight, low-bandwidth, and low-power environment. Typically, IoT devices connect to an LwM2M server and exchange data to perform actions like registration, updates, bootstrapping, or receiving commands.

The Vulnerability (CVE-2022-33294)

The vulnerability has been found in the code responsible for handling the reception of LwM2M messages related to registration, updates, and bootstrapping. A NULL pointer dereference occurs when the device tries to access a NULL pointer, leading to a crash and temporary unresponsiveness. This creates a transient DoS situation where the modem can't communicate effectively, possibly affecting the performance of the IoT devices connected to it.

The following code snippet demonstrates the underlying issue

int handle_lwm2m_message(struct lwm2m_message *message) {
  ...
  // Check if message is a response to a previous request
  if (message->type == RESPONSE) {
    struct lwm2m_request *request = find_matching_request(message);
    
    if (request == NULL) {
      // Error handling for NULL pointer dereference
      log_error("Received a response with no matching request");
      return -1;
    }

    // Processing response from LwM2M server
    process_lwm2m_response(request, message);
  }
  ...
}

In this code snippet, the handle_lwm2m_message() function checks if the received message is a response. If it is, the function attempts to find a matching request for the response using find_matching_request(). The issue occurs when this function returns a NULL pointer, as there is no proper error handling in place. As a consequence, the process_lwm2m_response() function attempts to process the response by accessing the NULL request object, leading to a NULL pointer dereference error and crashing the program.

In order to fix this vulnerability, proper error handling and validation should be implemented to ensure that the request object is not NULL before proceeding further into the processing of the LwM2M server's response.

Exploit Details

An attacker can exploit this vulnerability by sending crafted LwM2M response messages that trigger the NULL pointer dereference error. By doing so, the attacker can cause a temporary disruption in the modem's communications, which in turn affects the IoT devices connected to it.

To mitigate the risk posed by this vulnerability, users should implement proper error handling in the code, as described earlier. Additionally, it is recommended to keep devices updated with the latest security patches provided by the manufacturer to address such vulnerabilities.

Original References

1. CVE-2022-33294 entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-33294
2. OMA Lightweight M2M: https://openmobilealliance.org/iot/lightweight-m2m-lwm2m/
3. Modem Manufacturers with Security Updates: Example link (please replace with a link relevant to specific modem manufacturer)

Conclusion

This post has highlighted the transient DoS vulnerability in modem devices due to NULL pointer dereference while receiving responses to LwM2M registration/update/bootstrap request messages (CVE-2022-33294). We have delved into the code snippet demonstrating the issue, its impact, and how it can be exploited. It is essential for users to implement proper error handling in their code and keep their devices regularly updated with the latest security patches to protect against this and similar vulnerabilities.

Timeline

Published on: 04/13/2023 07:15:00 UTC
Last modified on: 04/21/2023 03:48:00 UTC