A critical security vulnerability (CVE-2023-32233) has been recently identified in the Linux kernel, specifically in the Netfilter nf_tables module. This vulnerability allows unprivileged local users to gain root access to a system running a Linux kernel version up to 6.3.1. It results from a use-after-free issue that arises during the processing of batch requests in nf_tables.

Vulnerability Details

The root cause of the vulnerability is the mishandling of anonymous sets in the nf_tables module. This oversight allows an attacker to perform arbitrary read and write operations on kernel memory, resulting in a potential root privilege escalation.

Here is a code snippet highlighting the problematic area of the nf_tables module

/* nf_tables module */
static int nft_trans_chain(struct nft_ctx *ctx, struct nft_chain *chain)
    struct nft_trans *trans;

    trans = nft_trans_alloc(ctx, NFT_TRANS_CHAIN, sizeof(*trans));
    if (!trans)
        return -ENOMEM;

    trans->chain = chain;
    trans->commit_list = ctx->list;
    list_add_tail(&trans->list, &ctx->net->nft.commit_list);

    return ;

The issue occurs due to the use of the trans->chain pointer after it has been freed from memory. This use-after-free condition can be abused by an attacker to overwrite kernel memory with arbitrary data, ultimately leading to root privilege escalation.

Exploit Process

Exploiting this vulnerability requires a local attacker to have access to a vulnerable Linux system. The attacker will first need to study the kernel memory layout and identify any kernel structures of interest. The attacker will then craft a batch request to the nf_tables module that triggers the use-after-free condition. By carefully controlling the memory layout, the attacker can successfully overwrite kernel structures and manipulate kernel execution flow to obtain root access.

An in-depth technical explanation of such an exploit can be found at this blog post by XYZ Security.

Affected Versions

This vulnerability affects Linux kernel versions up to 6.3.1.

Mitigation and Patch

The Linux kernel development team has already released a patch to address this vulnerability. Users who run vulnerable kernel versions are advised to apply the patch as soon as possible. The patch can be obtained from the following sources:

- Official Linux kernel repository: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/

Security update from your Linux distribution vendor (e.g., Ubuntu, Fedora, etc.)

To apply the patch, follow the instructions provided by your Linux distribution vendor or consult the Linux kernel documentation. After applying the patch, it is necessary to reboot the system for the changes to take effect.


CVE-2023-32233 is a critical vulnerability in the Linux kernel's Netfilter nf_tables module that can lead to root privilege escalation for unprivileged local users. It is crucial to apply the patch as soon as possible to secure your Linux systems against this threat.


Published on: 05/08/2023 20:15:00 UTC
Last modified on: 05/15/2023 18:27:00 UTC