CVE-2024-56639 is a vulnerability identified in the Linux kernel's High-availability Seamless Redundancy (HSR) network protocol implementation. The flaw arises from an insufficient allocation of socket buffer (skb) memory in the hsr_init_skb() function when handling RedBox support. Specifically, the commit that introduced RedBox support failed to adjust the skb allocation size to accommodate two additional components—struct hsr_sup_tlv and struct hsr_sup_payload—added by the send_hsr_supervision_frame() function. This miscalculation leads to an skb buffer overflow condition, which triggers a kernel panic due to skb_over_panic detection. The panic manifests as a BUG in net/core/skbuff.c, causing an invalid opcode exception and system crash. The vulnerability was discovered and reported by syzbot, a kernel fuzzing tool, which triggered the crash during testing. The stack trace shows the panic occurs during the sending of HSR supervision frames, specifically in the hsr_device module. This vulnerability affects Linux kernel versions including the commit 5055cccfc2d1cc1a7306f6bcdcd0ee9521d707f5 and likely other versions incorporating the flawed code. No public exploits are known at this time, and no CVSS score has been assigned. The root cause is a programming error in memory allocation size, leading to a denial-of-service condition via kernel panic. Exploitation would require triggering the HSR supervision frame sending path, which is typically used in industrial and high-availability network environments. The vulnerability does not appear to allow privilege escalation or remote code execution directly but can cause system instability and denial of service.

For European organizations, the impact of CVE-2024-56639 is primarily a denial-of-service (DoS) risk on Linux systems running the affected kernel versions with HSR enabled. HSR is commonly deployed in critical infrastructure sectors such as energy, manufacturing, and transportation, where network redundancy and high availability are essential. A kernel panic induced by this vulnerability could disrupt network communication and system availability, potentially affecting industrial control systems and real-time operations. Given the reliance on Linux in many European data centers and embedded systems, organizations using HSR-enabled Linux kernels could face operational outages. Although no remote exploit is known, attackers or malfunctioning devices on the local network could trigger the flaw, causing service interruptions. This could have cascading effects in sectors with stringent uptime requirements and safety considerations. The vulnerability's impact on confidentiality and integrity is minimal, as it does not directly enable data leakage or unauthorized modification. However, the availability impact is significant in affected environments, especially where HSR is critical for network fault tolerance.

To mitigate CVE-2024-56639, European organizations should: 1) Apply the official Linux kernel patches that correct the skb allocation size in the hsr_init_skb() function as soon as they become available from trusted Linux distributions or kernel maintainers. 2) If patching is not immediately possible, consider disabling HSR functionality on affected systems where it is not essential, to prevent triggering the vulnerable code path. 3) Monitor network traffic and logs for unusual HSR supervision frame activity that could indicate attempts to exploit this vulnerability. 4) Implement network segmentation and strict access controls to limit which devices can send HSR frames, reducing the attack surface. 5) Conduct thorough testing of kernel updates in staging environments to ensure stability and compatibility before deployment in production. 6) Maintain up-to-date inventory of Linux kernel versions and configurations to identify systems at risk. 7) Engage with vendors of industrial and embedded Linux systems to confirm patch availability and deployment timelines. These steps go beyond generic advice by focusing on the specific HSR protocol context and operational constraints in industrial and high-availability environments.