CVE-2024-26673 is a vulnerability identified in the Linux kernel's netfilter subsystem, specifically within the nft_ct (nftables connection tracking) component. The issue relates to insufficient sanitization of Layer 3 (network layer) and Layer 4 (transport layer) protocol numbers in custom expectations used by nftables. The vulnerability arises because the kernel previously allowed protocol families other than the intended NFPROTO_IPV4, NFPROTO_IPV6, and NFPROTO_INET, as well as Layer 4 protocols without mandatory destination port attributes. This lack of strict validation could allow malformed or unexpected protocol numbers to be processed, potentially leading to undefined behavior or security bypasses in packet filtering rules. The patch addresses this by explicitly disallowing protocol families outside the three specified and rejecting Layer 4 protocols that do not specify destination ports, which are mandatory for the nft_ct expectations object. Since nftables is widely used for firewall and packet filtering in Linux environments, this vulnerability could be exploited to bypass firewall rules or cause denial of service by corrupting connection tracking state or triggering kernel errors. However, as of the published date, there are no known exploits in the wild. The vulnerability affects multiple versions of the Linux kernel identified by the commit hash 857b46027d6f91150797295752581b7155b9d0e1, indicating a specific patch or kernel tree state. The lack of a CVSS score suggests the need for severity assessment based on technical impact and exploitability factors.

For European organizations, the impact of CVE-2024-26673 can be significant, especially for those relying heavily on Linux-based infrastructure for networking, servers, and security appliances. Since nftables is a core component for firewalling and connection tracking, exploitation could allow attackers to bypass firewall rules, leading to unauthorized network access or lateral movement within corporate networks. This could compromise confidentiality by exposing sensitive data or integrity by allowing malicious traffic to pass unchecked. Additionally, malformed packets exploiting this vulnerability could cause kernel crashes or denial of service, impacting availability of critical services. Organizations in sectors such as finance, healthcare, telecommunications, and government, which often use Linux-based firewalls or routers, may face increased risk. The absence of known exploits currently reduces immediate threat but does not eliminate the risk of future weaponization. Given the widespread use of Linux in European data centers and cloud environments, unpatched systems could be targeted by attackers aiming to evade network defenses or disrupt services.

European organizations should prioritize applying the official Linux kernel patches that sanitize Layer 3 and Layer 4 protocol numbers in nft_ct custom expectations. Specifically, updating to kernel versions that include the fix identified by commit 857b46027d6f91150797295752581b7155b9d0e1 or later is essential. Network administrators should audit nftables configurations to ensure no custom expectations rely on unsupported protocol families or Layer 4 protocols without destination ports. Implementing strict input validation and monitoring for anomalous network traffic patterns that could exploit malformed protocol numbers is recommended. Additionally, organizations should employ kernel hardening techniques such as enabling kernel lockdown modes and using security modules like SELinux or AppArmor to limit potential damage from kernel-level exploits. Regular vulnerability scanning and penetration testing focused on firewall and connection tracking components can help detect exploitation attempts. Finally, maintaining an incident response plan that includes kernel-level vulnerabilities will improve readiness against potential attacks exploiting this issue.