CVE-2024-35840 is a vulnerability identified in the Linux kernel's implementation of Multipath TCP (MPTCP), specifically within the subflow_finish_connect() function. MPTCP is an extension of TCP that allows multiple paths to be used simultaneously between two endpoints, improving redundancy and throughput. The vulnerability arises because subflow_finish_connect() relies on four fields—backup, join_id, thmac, and none—that may contain uninitialized or garbage data unless the OPTION_MPTCP_MPJ_SYNACK flag has been properly set during the parsing of MPTCP options in mptcp_parse_option(). This improper handling can lead to the use of invalid or unpredictable values during subflow connection finalization. While the exact impact is not explicitly detailed, the presence of garbage data in critical connection parameters could potentially lead to undefined behavior, including memory corruption, denial of service (DoS), or other stability issues within the kernel networking stack. The vulnerability affects specific Linux kernel versions identified by commit hashes, indicating that it is present in certain recent or development builds. No known exploits are reported in the wild at this time, and no CVSS score has been assigned yet. The issue was publicly disclosed on May 17, 2024, and has been acknowledged by the Linux project with a patch presumably available or forthcoming to ensure the OPTION_MPTCP_MPJ_SYNACK flag is correctly set before these fields are used.

For European organizations, this vulnerability could have significant implications, especially for those relying on Linux-based infrastructure that utilizes MPTCP for enhanced network performance and reliability. Potential impacts include system instability or crashes due to kernel memory corruption, which could disrupt critical services and applications. Organizations operating data centers, cloud services, or telecommunications infrastructure that leverage MPTCP might experience degraded network performance or outages if exploited. Although no active exploits are currently known, the vulnerability could be leveraged by attackers to cause denial of service or potentially escalate privileges if combined with other vulnerabilities. This risk is heightened in sectors with high availability requirements such as finance, healthcare, and government services. Additionally, the complexity of MPTCP means that debugging and mitigation may require specialized knowledge, potentially delaying remediation efforts and increasing exposure time.

European organizations should prioritize updating their Linux kernel to the latest patched versions that address CVE-2024-35840. Specifically, system administrators should: 1) Identify all systems running affected Linux kernel versions, particularly those using MPTCP features. 2) Apply vendor-provided patches or upgrade to kernel versions where the OPTION_MPTCP_MPJ_SYNACK flag handling has been corrected. 3) If immediate patching is not feasible, consider disabling MPTCP functionality temporarily to mitigate risk, understanding this may impact network performance. 4) Monitor kernel logs and network behavior for anomalies that could indicate exploitation attempts or instability. 5) Incorporate this vulnerability into vulnerability management and incident response plans to ensure rapid detection and remediation. 6) Engage with Linux distribution vendors for timely updates and guidance. 7) Conduct thorough testing in staging environments before deploying patches to production to avoid unintended service disruptions.