CVE-2024-26863 is a vulnerability identified in the Linux kernel's High-availability Seamless Redundancy (HSR) network protocol implementation. The issue arises from an uninitialized value access in the function hsr_get_node(), specifically when processing Ethernet frames with packet type IDs ETH_P_PRP or ETH_P_HSR that are not followed by an HSR tag. The kernel's Kernel Memory Sanitizer (KMSAN) detected that in such cases, the function hsr_get_skb_sequence_nr() reads an invalid sequence number value, leading to undefined behavior. This uninitialized memory read occurs because the code does not properly verify the presence of the HSR tag following the Ethernet header before accessing the sequence number. The vulnerability is rooted in the net/hsr/hsr_framereg.c and related source files, affecting the packet forwarding and transmission logic within the HSR network device driver. The patch resolves the issue by adding a check that returns NULL if the Ethernet header is not followed by an HSR tag, preventing the use of uninitialized data. This flaw could potentially be triggered by crafted network packets that exploit the improper validation of HSR frames, leading to kernel memory corruption or information leakage. However, there is no evidence of known exploits in the wild at this time. The vulnerability affects Linux kernel versions including and around commit f266a683a4804dc499efc6c2206ef68efed029d0, and it was publicly disclosed on April 17, 2024. The vulnerability does not have an assigned CVSS score but is recognized by CISA and Linux maintainers.

For European organizations, the impact of CVE-2024-26863 depends largely on the deployment of Linux systems utilizing the HSR protocol, which is primarily used in industrial and critical infrastructure networks requiring high availability and redundancy, such as power grids, manufacturing plants, and transportation systems. Exploitation could lead to kernel memory corruption, potentially causing system instability, crashes, or information disclosure. This could disrupt critical services or expose sensitive operational data. Given that HSR is used in high-availability environments, any instability could have cascading effects on industrial control systems and network reliability. Although no active exploits are known, the vulnerability could be leveraged by attackers with network access to send specially crafted Ethernet frames to vulnerable hosts, potentially bypassing some security controls due to the low-level nature of the flaw. Confidentiality, integrity, and availability of affected systems could be compromised, impacting operational continuity and safety in sectors critical to European economies and public services.

European organizations should prioritize updating their Linux kernel to versions that include the patch for CVE-2024-26863 as soon as possible. Specifically, kernel versions incorporating the fix that returns NULL when the Ethernet header is not followed by an HSR tag should be deployed. Network segmentation should be enforced to limit exposure of HSR-enabled devices to untrusted networks, reducing the attack surface. Monitoring network traffic for anomalous or malformed HSR and PRP frames can help detect potential exploitation attempts. Industrial control system operators should validate their Linux-based network devices and embedded systems for this vulnerability and apply vendor-provided patches or kernel updates. Additionally, organizations should implement strict access controls and network filtering at the data link layer to prevent unauthorized injection of crafted Ethernet frames. Regular security audits and penetration testing focusing on network protocol implementations can help identify residual risks. Finally, maintaining up-to-date incident response plans for industrial network disruptions is advisable.