CVE-2024-26708 is a medium-severity vulnerability identified in the Linux kernel's implementation of Multipath TCP (MPTCP), specifically related to the handling of TCP Fast Open and path management (PM) triggered subflow shutdown. The vulnerability arises from a race condition between the Fast Open mechanism and the shutdown of subflows triggered by path management. In the initial fix attempt, the Linux kernel developers overlooked the possibility that the subflow's state could change again before the subflow_state_change callback is invoked. This oversight could lead to inconsistent or unexpected states during TCP connection teardown, particularly states reachable from TCP_FIN_WAIT1. The vulnerability does not affect confidentiality or integrity but impacts availability, as the race condition can cause subflows to be improperly closed or left in an inconsistent state, potentially leading to denial of service or degraded network performance. The CVSS 3.1 base score is 5.5, reflecting a medium severity with a vector indicating local attack vector (AV:L), low attack complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), no confidentiality or integrity impact (C:N/I:N), but high impact on availability (A:H). No known exploits are currently reported in the wild. The vulnerability affects specific Linux kernel versions identified by commit hashes, implying that it is relevant to systems running affected kernel builds prior to the patch. The fix involves more comprehensive handling of subflow states, ensuring that all states reachable from TCP_FIN_WAIT1 are properly managed to prevent race conditions.

For European organizations, the impact of CVE-2024-26708 primarily concerns systems running Linux kernels with Multipath TCP enabled and using TCP Fast Open features. Such systems could experience degraded network reliability or denial of service conditions due to improper subflow shutdowns. This can affect critical infrastructure, cloud services, telecommunications, and enterprises relying on Linux-based servers or network appliances. Given the medium severity and local attack vector, exploitation requires local access or low-privilege user capabilities, limiting remote exploitation risks but increasing concerns for multi-tenant environments, shared hosting, or containerized deployments common in European data centers. Disruptions in network connectivity or service availability could impact business continuity, especially in sectors like finance, healthcare, and public services. However, the absence of confidentiality or integrity impact reduces the risk of data breaches. The lack of known exploits in the wild suggests a lower immediate threat but does not preclude targeted attacks or exploitation in the future.

European organizations should prioritize patching Linux kernels to versions that include the fix for CVE-2024-26708. Specifically, updating to the latest stable kernel releases where the race condition in MPTCP Fast Open handling is resolved is critical. Organizations should audit their environments to identify systems using Multipath TCP and TCP Fast Open features and assess whether these features are necessary; if not, consider disabling them to reduce the attack surface. For environments where local user access is possible, implement strict access controls and user privilege restrictions to minimize the risk of local exploitation. Monitoring kernel logs and network behavior for anomalies related to TCP subflow states can help detect potential exploitation attempts. Additionally, organizations employing containerization or virtualization should ensure host kernels are patched, as guest systems may be affected indirectly. Network segmentation and limiting local user capabilities on critical systems further reduce risk. Finally, maintain awareness of vendor advisories and security bulletins for updates or emerging exploit reports.