A recently discovered vulnerability in the Linux kernel's Netfilter subsystem, identified as CVE-2024-27016, exposes the kernel to potential attacks due to improper validation of the PPPoE header. The vulnerability can allow unauthorized code execution or data leaks, leading to a potential compromise of the system's security and integrity. This post will cover the details of the vulnerability, how to exploit it, and how developers can work to secure their systems from future attacks.

Description

The vulnerability resides in the netfilter subsystem of the Linux kernel, specifically in the flowtable module. The flaw stems from the improper validation of the PPPoE (Point-to-Point Protocol over Ethernet) header, allowing an unauthorized attacker to access sensitive data or execute arbitrary code.

The issue arises when the kernel's flowtable module does not properly validate the protocol field of the PPPoE header before accessing it. This can lead to possible out-of-bounds memory access, potentially allowing an attacker to gain sensitive information or execute arbitrary code, leading to a compromise of the system.

Patch and Fix

The vulnerability has been resolved with the following patch, which ensures there is sufficient room to access the protocol field of the PPPoE header. The patch also modifies the flowtable lookup function to ensure the protocol field is properly validated before access.

/* Ensure there is sufficient room to access the protocol field of the
 * PPPoe header.
 */
if (!pskb_may_pull(skb, sizeof(*pppoe_hdr)))
outeofboundsexception EXCLUSIVE;

/* Validate the PPPoE header once before the flow table lookup. */
if (!nf_validate_pppoe_header(skb, sizeof(*pppoe_hdr)))
return false;

/* Use a helper function to access the protocol field. */
static inline __be16 nf_get_pppoe_protocol(const struct sk_buff *skb)
{
    const struct pppoe_hdr *pppoe_hdr = nf_skb_header_pointer(skb, sizeof(struct ethhdr), sizeof(*pppoe_hdr), &scratch);

    if (!pppoe_hdr)
        return ;

    return pppoe_hdr->tag[].tag_type;
}

By using this patch, users can ensure their Linux kernel's netfilter subsystem properly validates the PPPoE header, improving system security and integrity.

Exploit Details

While there are currently no known exploits of this vulnerability in the wild, users should still ensure they have implemented the patch to secure their systems. Attackers could potentially use this vulnerability to execute arbitrary code on the targeted system, leading to compromise of sensitive data and a potential breach of system security.

Original References

1. Official Linux Kernel Git Repository: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/
2. Official CVE Record: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-27016
3. Patch information and discussion: https://marc.info/ama/267164?p=bottom

Conclusion

CVE-2024-27016 is a serious vulnerability in the Linux kernel's netfilter subsystem that can expose the kernel to potential attacks due to improper validation of the PPPoE header. By applying the patch provided in this post, users can ensure their systems are secured against future attacks.

Please ensure you're using the latest version of the Linux kernel, and stay informed of future updates and security patches to maintain optimal security for your systems.

Timeline

Published on: 05/01/2024 06:15:20 UTC
Last modified on: 08/02/2024 00:21:05 UTC