CVE-2022-25745: Memory Corruption in Modem Due to Improper Input Validation While Handling the Incoming CoAP Message

A new vulnerability, identified as CVE-2022-25745, has been discovered that affects modems and could result in memory corruption. This vulnerability occurs due to improper input validation while handling incoming CoAP (Constrained Application Protocol) messages. In this post, we will take a deeper look at the vulnerability, including details about the affected devices, a code snippet exemplifying the issue, and links to original references. Finally, we will discuss the potential exploit scenarios and how to mitigate this vulnerability.

Background

CoAP is a specialized web transfer protocol designed for use in resource-constrained environments, such as low-power sensors, switches, and other embedded devices. It is primarily used for machine-to-machine (M2M) communication and Internet of Things (IoT) applications. CoAP allows devices to communicate with each other using a simple request-response model, with messages being exchanged in a compact binary format.

Affected Devices

The CVE-2022-25745 vulnerability affects modems that support CoAP-based M2M communication. At this time, specific models and vendors have not been publicly disclosed. It is recommended to check with your modem vendor for any available patches or updates.

Code Snippet

The vulnerability lies in the improper validation of incoming CoAP messages on the affected modem, which might result in memory corruption. The following code snippet demonstrates a simplified version of the issue:

#include <stdint.h>
#include <string.h>
#include <stdlib.h>

void handle_coap_message(uint8_t *message, size_t message_len) {
    // Simplified CoAP message header
    typedef struct {
        uint8_t version_type_and_token_len;
        uint8_t code;
        uint16_t message_id;
    } coap_hdr_t;

    coap_hdr_t *header = (coap_hdr_t *)message;

    // Issue: No proper input validation for message_len here
    uint8_t token_len = (header->version_type_and_token_len & xF);

    // Define a buffer for the token
    uint8_t token[8];

    // Issue: Possible memory corruption if token_len is larger than 8
    memcpy(token, message + sizeof(coap_hdr_t), token_len);
}

In the code snippet above, the 'token_len' is extracted from the incoming CoAP message without proper validation. The subsequent 'memcpy' function may cause memory corruption if the 'token_len' value is larger than the size of the 'token' buffer.

Exploit Details

An attacker could craft a malicious CoAP message with an oversized token length value, potentially resulting in memory corruption on the target modem. This could allow the attacker to execute arbitrary code, cause a denial of service (DoS), or access sensitive information.

Mitigations

To mitigate this vulnerability, device vendors should apply the following improvements to their firmware:

Original References

1. CoAP (Constrained Application Protocol) - IETF
2. Request for Comments (RFC) 7252 - The Constrained Application Protocol

Conclusion

The CVE-2022-25745 vulnerability highlights the importance of proper input validation when handling incoming messages in resource-constrained devices. By understanding the nature of the vulnerability, its impact, and recommended mitigations, users and vendors can take the necessary steps to ensure the security of their devices and the networks they support.

Timeline

Published on: 04/13/2023 07:15:00 UTC
Last modified on: 04/24/2023 16:20:00 UTC