CVE-2024-26924 is a medium-severity vulnerability affecting the Linux kernel's netfilter subsystem, specifically within the nft_set_pipapo component responsible for managing sets of network filtering elements. The vulnerability arises from improper handling of element removal in sets when multiple elements share the same key, particularly under conditions involving rapid add/remove operations with timeouts. The removal process involves two steps: marking an element as inactive in the next generation and then removing it from the set. However, if there are multiple elements with the same key—where one is inactive or timed out—the removal function may incorrectly unmap the wrong element. This leads to a stale pointer scenario where a deactivated element remains reachable in the data structure, causing potential use-after-free conditions and kernel crashes when the stale element is accessed during lookups. The root cause is a missing verification that the key fully matches the element marked inactive before removal, which the patch addresses by adding this check and a bug trap to prevent removal of invisible or non-existent elements. The vulnerability is identified as CWE-476 (NULL Pointer Dereference) and has a CVSS 3.1 base score of 5.9, reflecting a network attack vector with high attack complexity, no privileges or user interaction required, and an impact limited to availability (kernel crashes). No known exploits are currently reported in the wild. The affected versions correspond to specific Linux kernel commits prior to the fix published in April 2024.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable Linux kernel versions with netfilter sets configured in environments that perform rapid, back-to-back add/remove operations on network filtering elements. The impact is a denial-of-service condition due to kernel crashes, which can disrupt critical network functions, firewall operations, or other security controls relying on nftables. This can lead to temporary loss of availability of network services, impacting business continuity, especially in sectors relying heavily on Linux-based infrastructure such as telecommunications, cloud service providers, and critical infrastructure operators. While the vulnerability does not directly compromise confidentiality or integrity, the resulting instability could be exploited as part of a broader attack chain to degrade defenses or cause operational disruptions. Given the medium severity and absence of known exploits, the immediate risk is moderate but warrants timely patching to prevent potential exploitation in complex network environments.

European organizations should promptly update their Linux kernels to versions containing the fix for CVE-2024-26924. Specifically, they should apply the latest stable kernel releases or backported patches from their Linux distribution vendors that address the nft_set_pipapo removal logic. Network administrators should audit nftables configurations to identify sets with high-frequency add/remove operations and consider temporarily reducing such operations or implementing rate limiting until patches are applied. Monitoring kernel logs for KASAN (Kernel Address Sanitizer) splats or related crash signatures can help detect attempts to trigger this vulnerability. Additionally, organizations should enforce strict kernel update policies, especially on critical network infrastructure and firewall devices, and validate kernel integrity post-update. For environments where immediate patching is not feasible, isolating vulnerable systems from untrusted networks or restricting access to network management interfaces can reduce exposure. Finally, maintain up-to-date backups and incident response plans to quickly recover from potential denial-of-service incidents.