CVE-2023-31248 - Linux Kernel nftables Use-After-Free Local Privilege Escalation Vulnerability Exploitation

A recently discovered vulnerability in the Linux Kernel (CVE-2023-31248) has been causing quite a stir in the IT security world. This vulnerability is a local privilege escalation bug affecting the nftables subsystem, which can result in unauthorized access escalation. This post will explore this vulnerability, including details about the exploit, code snippets involved, and the related information from original references.

Synopsis

CVE-2023-31248 specifically targets the nftables subsystem's nft_chain_lookup_byid() function, which fails to check whether a chain is active and if CAP_NET_ADMIN is present in any user or network namespace. Consequently, this allows an attacker to trigger a use-after-free situation, which can further lead to local privilege escalation.

Let's take a closer look at the exploit and the involved code snippets.

Code Snippet

The core of this exploit lies in the Linux kernel's code for nftables. Below is a simple code excerpt highlighting the problematic section:

struct nft_chain *nft_chain_lookup_byid(const struct nfgenmsg *nfmsg,
					const struct nlattr * const tb[],
					u32 id, u8 genmask)
{
	struct nft_table *table;
	struct nft_chain *chain;

	if (nfmsg->nfgen_family == NFPROTO_UNSPEC)
		return ERR_PTR(-EOPNOTSUPP);

	table = nft_table_lookup(nfmsg, tb);
	if (IS_ERR(table))
		return ERR_CAST(table);

	chain = nft_chain_lookup(table, id, genmask);
	if (!chain)
		return ERR_PTR(-ENOENT);

	return chain;
}

As shown above, nft_chain_lookup_byid() does not perform a check on the chain's active state and whether CAP_NET_ADMIN is present for the user or network namespace. This omission can make it susceptible to exploitation.

Exploit Details

To exploit this vulnerability, a local unprivileged attacker must first create a crafted nftables rule and execute it. By doing so, the attacker can craft an nftables update that triggers a use-after-free condition. This, in turn, allows the attacker to gain write access to memory, potentially leading to arbitrary code execution.

Achieve arbitrary code execution and escalate privileges

For a detailed understanding of the exploitation process, it's essential to consult original references and expert analysis.

The following official sources have provided valuable information regarding CVE-2023-31248

1. CVE Record: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-31248
2. NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-31248

These sources offer a comprehensive synopsis of the vulnerability, along with the assigned severity and related technical details.

Mitigation

To address the aforementioned vulnerability and safeguard your system from potential exploitation, it's crucial to apply recent security patches. This may include updating your Linux kernel and ensuring that your security policies are up-to-date.

Conclusion

CVE-2023-31248 is a serious vulnerability in the Linux Kernel, which can allow local privilege escalation due to the absence of key security checks. Understanding this vulnerability is vital in order to apply the necessary security patches and safeguard your systems and data. In a world where cyber threats are continually evolving, staying informed and proactive is the best way to ensure protection from potential security breaches.

Timeline

Published on: 07/05/2023 19:15:00 UTC
Last modified on: 08/02/2023 17:15:00 UTC