A worrisome vulnerability, CVE-2023-6111, has been discovered in the Linux kernel's netfilter, specifically in the nf_tables component. This vulnerability can be exploited by an attacker for local privilege escalation, allowing them to execute code on a target machine with higher privileges. This poses a significant threat to the security of Linux systems and their users. In this post, we will provide details about how this vulnerability works, examine the code, and provide recommendations for mitigating the risk.

Vulnerability Background

The use-after-free vulnerability is a result of an issue in the nft_trans_gc_catchall function, which improperly handles the removal of catchall set element from the catchall_list when the sync argument is true. This allows the catchall set element to be freed multiple times, which can lead to a use-after-free situation.

The faulty code can be found in the following snippet

void nft_trans_gc_catchall(struct nft_trans *trans, bool sync)
    if (sync) {
        nft_set_elem_destroy(set, elem);
        nft_set_elem_deactivate(set, trans, elem);

As you can see, if the sync argument is true, the catchall set element is freed through the nft_set_elem_destroy() function, and then deactivated with nft_set_elem_deactivate(). However, there is no instruction to remove the catchall set element from the catchall_list, which leads to the use-after-free vulnerability.

Exploiting the Vulnerability

To exploit this vulnerability and achieve local privilege escalation, an attacker can take advantage of the use-after-free situation by constructing a specific attack payload. This payload would need to be designed to manipulate the freed memory in a way that allows the attacker to overwrite critical kernel data and redirect code execution to their malicious code.

Given how prevalent the Linux kernel is in numerous operating systems and devices, this vulnerability could have serious implications if left unpatched. It is absolutely crucial that systems running the affected version of the kernel are updated as soon as possible to guard against potential exploitation.

Mitigation Steps

The Linux kernel development team has addressed this vulnerability in commit 93995bf4af2c5a99e2a87fcd5ce547d31eb763, which ensures proper handling of catchall set element removal when the sync argument is true. You can find the commit details here:

- Linux Kernel GitHub Commit

We highly recommend upgrading your Linux kernel to a version that includes this commit, as it provides protection against this vulnerability. Please consult your distribution's documentation and security advisories for information on the specific kernel version you should upgrade to.

In conclusion, CVE-2023-6111 represents a severe use-after-free vulnerability in the Linux kernel's netfilter component that can be exploited for local privilege escalation. It is crucial that system administrators apply the necessary patches as soon as possible to ensure the security of their systems. Remember to always keep your systems up-to-date and follow best security practices.


Published on: 11/14/2023 14:15:29 UTC
Last modified on: 11/18/2023 03:27:23 UTC