CVE-2024-46711 is a vulnerability identified in the Linux kernel's implementation of Multipath TCP (MPTCP), specifically related to the path manager (pm) handling of the initial subflow endpoint (ID 0). MPTCP allows a single TCP connection to use multiple paths to maximize resource usage and increase redundancy. The vulnerability arises from improper management of internal counters 'local_addr_used' and 'add_addr_accepted' when the initial subflow's entrypoint is removed and re-added multiple times during a connection lifecycle. These counters track the usage of local addresses and the acceptance of additional addresses for subflows. The flaw is that these counters are decremented for addresses not related to the initial subflow, which should not happen since the initial subflow's source and destination addresses are known upfront and are not considered additional addresses. Consequently, when the initial subflow's entrypoint is removed and re-added more than once, the counters are incorrectly incremented or decremented, leading to inconsistent internal state management. This can cause the entrypoint to fail to be removed and re-added properly, potentially disrupting MPTCP connection stability or causing unexpected behavior in connection management. While no known exploits are reported in the wild, the vulnerability affects the Linux kernel versions identified by the commit hash 3ad14f54bd7448384458e69f0183843f683ecce8 and likely related kernel versions incorporating this code. The issue has been addressed by correcting the counter increment/decrement logic to ensure that the initial subflow's addresses are handled correctly during entrypoint removal and re-addition. This fix prevents the internal state inconsistencies that could otherwise lead to connection management errors in MPTCP-enabled Linux systems.

For European organizations, the impact of CVE-2024-46711 depends largely on the deployment of Linux systems utilizing MPTCP, which is increasingly used in environments requiring high availability and bandwidth aggregation, such as data centers, telecommunications infrastructure, and cloud services. Disruption or instability in MPTCP connections could lead to degraded network performance, intermittent connectivity issues, or failures in multi-path routing scenarios. This may affect critical services relying on resilient network connections, including financial services, healthcare systems, and industrial control systems that use Linux-based infrastructure. While the vulnerability does not directly lead to remote code execution or privilege escalation, the potential for denial of service or connection disruption could impact availability and reliability of network services. Given the widespread use of Linux in European IT environments, especially in servers and network appliances, organizations could experience operational disruptions if vulnerable kernel versions are in use and MPTCP is enabled. However, the lack of known exploits and the technical nature of the flaw suggest the immediate risk is moderate but should not be ignored, especially in high-availability or critical network environments.

European organizations should prioritize updating Linux kernel versions to those that include the fix for CVE-2024-46711. Specifically, applying the latest stable kernel releases or vendor-provided patches that address the MPTCP path manager logic is essential. Network administrators should audit their systems to identify where MPTCP is enabled and assess whether the kernel versions in use are affected. In environments where immediate patching is not feasible, temporarily disabling MPTCP or the affected path manager components can mitigate the risk of connection instability. Additionally, monitoring network logs and connection metrics for anomalies related to MPTCP subflow management can help detect potential exploitation attempts or operational issues. Organizations should also engage with Linux distribution vendors and security advisories to receive timely updates and guidance. Implementing robust network segmentation and limiting exposure of critical Linux systems to untrusted networks can further reduce risk. Finally, incorporating this vulnerability into vulnerability management and incident response plans ensures preparedness for any emerging threats exploiting this flaw.