A recently discovered vulnerability, CVE-2023-3863, exposes a use-after-free flaw in the Linux kernel's Near Field Communication (NFC) implementation. This vulnerability, specifically found in nfc_llcp_find_local() function within net/nfc/llcp_core.c, allows a local user with special privileges to cause a kernel information leak issue potentially leading to further exploitation. In this post, I provide an in-depth look at this vulnerability, explain the code snippet responsible for it, discuss the impact of the exploit, and suggest necessary mitigations. To better understand the issue, we will also explore relevant links and original references.

Code Snippet

The vulnerable code block, part of the nfc_llcp_find_local function in net/nfc/llcp_core.c, reads as follows:

struct nfc_llcp_local *nfc_llcp_find_local(struct nfc_dev *dev)
{
    struct nfc_llcp_local *local;

    list_for_each_entry(local, &local_list, list) {
        if (local->dev == dev)
            return local;
    }

    return NULL;
}

In this snippet, the list_for_each_entry macro iterates through a list of nfc_llcp_local objects. The function returns a pointer to a local nfc_llcp_local object if it matches a given nfc_dev object.

Exploit Details

This use-after-free flaw is triggered if an attacker can take advantage of a situation where the function is called for an object that has already been freed but not removed from the local_list, effectively giving the attacker access to the freed memory. This can potentially lead to a kernel information leak issue, which can act as a stepping stone for further kernel-level exploits.

Since the flaw requires a local user with special privileges, it limits the potential attack surface to users with access to the system in question. However, if an attacker has already gained these privileges, this vulnerability can have severe consequences, potentially allowing for additional kernel-level exploits.

1. Official NVD Entry for CVE-2023-3863
2. Linux kernel source code for NFC
3. Mitre CVE Description

Mitigations

While a patch for this vulnerability is not yet available, there are few steps that can be taken to mitigate its impact:

1. Restrict access: Ensuring that only trusted users and applications have access to the affected system, and keeping the number of users with special privileges to a minimum, can help reduce the likelihood of successful exploitation.
2. Update the kernel: Regularly update the Linux kernel and apply patches to address the latest security vulnerabilities.
3. Monitor system logs: Regularly examine system logs for unusual activities or access patterns that could indicate exploits.

Conclusion

CVE-2023-3863, a use-after-free vulnerability in the Linux kernel's NFC implementation, is a serious flaw that can potentially lead to kernel information leaks and escalate into further exploitation. Understanding the underlying code and the specifics of the exploit is essential to increased cybersecurity awareness and defense against attacks. While waiting for an official patch, do not hesitate to apply the mitigation strategies mentioned above and stay vigilant in monitoring your system's health.

Timeline

Published on: 07/24/2023 15:15:00 UTC
Last modified on: 08/19/2023 18:17:00 UTC