A recently discovered vulnerability in the Linux kernel (CVE-2024-27015) affects the way the kernel handles netfilter flowtable entries for PPPoE (Point-to-Point Protocol over Ethernet) traffic. Improper handling of PPPoE traffic in the ingress path can lead to a mismatch in flow table entries, causing PPPoE packets to be forwarded along the classical forwarding path, potentially impacting network performance.
This article will discuss the details of the vulnerability, along with a code snippet from the Linux kernel source code, and links to the original references. We will also look into the exploit details and the potential implications of this vulnerability.
Vulnerability Details
The Linux kernel netfilter subsystem is responsible for managing packet filtering, network address translation (NAT), and various other packet-related tasks. This particular vulnerability affects the flowtable component of the netfilter subsystem and deals with the incorrect handling of PPPoE tuples.
In the ingress path of PPPoE packets, the Linux kernel expects the PPPoE header to be present at the network header offset. However, due to the current implementation, this expectation is not met, leading to a mismatch in the flow table lookup. This results in PPPoE packets being forwarded through the classical forwarding path instead of following the flow table-defined path.
Code Snippet
The following code snippet, taken from the Linux kernel source code, demonstrates the incorrect assumption made about the location of the PPPoE header:
static int nf_flow_table_pppoe_lookup(struct sk_buff *skb, struct sw_flow_key *key)
{
struct pppoe_hdr *ph;
if (skb->len < sizeof(*ph))
return -1;
ph = skb_header_pointer(skb, skb_network_offset(skb), sizeof(*ph), &ph);
if (!ph || ph->ver != 1 || ph->type != 1)
return -1;
return ;
}
In this snippet, the 'sk_buff' structure represents the network packet. The pointer to the PPPoE header (ph) is retrieved using the 'skb_header_pointer()' function, which uses 'skb_network_offset()' to determine the network header offset. The code then checks for a valid PPPoE header, but the header might not be present at the expected location, causing a flow table mismatch.
Original References
The vulnerability was originally reported by the National Institute of Standards and Technology (NIST):
- NIST National Vulnerability Database (NVD) - CVE-2024-27015
Additionally, the Linux kernel source code can be found at the following location
Exploit Details
At the time of writing, there are no known exploits that take advantage of this vulnerability. However, the potential impact of this vulnerability includes reduced network performance due to PPPoE packets being forwarded along the classical forwarding path instead of the flow table-defined path.
While there's no direct security risk associated with this vulnerability, network administrators using Linux-based systems with netfilter and PPPoE traffic should be aware of this issue and consider updating their Linux kernel to a version that has addressed the problem.
Conclusion
The Linux Kernel vulnerability CVE-2024-27015, involving incorrect PPPoE tuple handling in the netfilter flowtable, can potentially impact network performance for systems relying on PPPoE traffic. To mitigate this issue, it is essential to update the Linux kernel to a patched version, which correctly handles PPPoE header locations and avoids flow table lookups mismatch. By staying informed about such vulnerabilities and keeping systems up-to-date, network administrators can ensure smooth network performance and maintain the stability and security of their environments.
Timeline
Published on: 05/01/2024 06:15:20 UTC
Last modified on: 06/14/2024 18:55:59 UTC