In this long-read technical post, we will delve deep into the details of the CVE-2023-42753 vulnerability. This vulnerability is an array indexing issue that was discovered in the netfilter subsystem of the Linux kernel. It has the potential to enable a local user to crash the system or, even worse, escalate their privileges on the system.

This article provides an introductory understanding of the vulnerability, its exploitation details, code snippets demonstrating the problem, and links to original references in an effort to elucidate the matter. Let's dive in!

Vulnerability Overview

The CVE-2023-42753 vulnerability is associated with the netfilter subsystem of the Linux kernel, which is responsible for the packet filtering system that manages inbound and outbound traffic on a Linux device. The vulnerability specifically lies in the handling of the h->nets array offset due to a missing macro, which leads to a miscalculation. As a result, attackers can take advantage of this primitive to arbitrarily increment or decrement a memory buffer out-of-bound.

The affected versions are Linux kernels prior to 5.3. Check for patches and updated kernel versions to avoid this vulnerability.

How the Code is Affected

The problematic section of the code can be found in the 'net/netfilter/nf_tables_api.c' file. Below is the excerpt:

static void nft_chain_eval(struct nft_pktinfo *pkt, struct nft_data *data, const struct nft_chain *chain)
{
    const struct nft_base_chain *basechain = nft_base_chain(chain);
    const struct nft_rule *rule;
    int verdict = NFT_JUMP_STACK_SIZE;
    unsigned int eval = ;
    u8 stack[basechain->stacksize]
            __aligned(__alignof__(u64));
}

The above code snippet reveals that the size of the stack array is calculated based on basechain->stacksize. However, there is no macro available to ensure the calculation of the h->nets array offset is accurate. This results in the array indexing issue that subsequently causes the vulnerability.

Exploit Detail

An attacker could take advantage of this vulnerability by manipulating the miscalculated h->nets array offset. As previously mentioned, this error allows attackers to perform arbitrary increment and decrement operations on a memory buffer located out-of-bound. In doing so, they could potentially crash the system or exploit it for privilege escalation.

It is essential to note that taking advantage of this vulnerability typically requires local access to the system. As such, the impact on remote or external threats is relatively limited. Nevertheless, the vulnerability still constitutes a significant security risk, especially in multi-user environments where an attacker could exploit the elevated privileges to compromise other users, data, or system stability.

Original References

To read more about the CVE-2023-42753 vulnerability and its impact on the Linux kernel, please refer to the following sources:

1. CVE Details of CVE-2023-42753
2. National Vulnerability Database: CVE-2023-42753

These resources provide a wealth of information about the vulnerability, including details about affected versions, known exploits, and any additional pertinent information regarding the issue. You can use these references to further understand the vulnerability and the potential consequences it poses to the Linux kernel and your system.

Conclusion

In conclusion, the CVE-2023-42753 vulnerability poses a significant threat to the security and stability of the Linux kernel, particularly in multi-user environments. Due to an array indexing issue in the netfilter subsystem, this vulnerability can enable local users to crash the system or escalate their privileges. It is crucial to be aware of this vulnerability and take the necessary precautions to ensure that your system remains secure and up-to-date.

To mitigate this risk, ensure that your Linux kernel is updated to at least version 5.3 or apply the necessary patches provided by your Linux distribution vendor. Keep an eye on the official security advisories and updates to protect your system from potential threats stemming from this vulnerability.

Timeline

Published on: 09/25/2023 21:15:00 UTC
Last modified on: 10/16/2023 19:41:00 UTC