CVE-2024-26631 is a concurrency vulnerability in the Linux kernel's IPv6 multicast implementation, specifically within the functions ipv6_mc_down and mld_ifc_work. The root cause is a data race condition on the variable idev->mc_ifc_count, which is accessed and modified without proper synchronization. This can lead to inconsistent or corrupted state in the multicast interface count due to concurrent writes. The vulnerability was identified by syzbot, a kernel fuzzing tool, which detected a data race condition flagged by the Kernel Concurrency Sanitizer (KCSAN). The fix involves enforcing proper locking by wrapping calls to mld_ifc_stop_work() and mld_gq_stop_work() with mutex_lock() and mutex_unlock() to ensure that these functions are only called while holding the mc_lock mutex, as originally intended by their design. The vulnerability affects the Linux kernel's IPv6 multicast code path, which is responsible for managing multicast listener discovery (MLD) and multicast group membership on network interfaces. The data race occurs during network interface state changes, such as when interfaces go down or multicast group memberships are updated, potentially causing kernel memory corruption or unpredictable behavior. Although no known exploits are currently reported in the wild, the vulnerability could be triggered by local or remote events that cause network interface state changes or multicast group updates. The affected versions are identified by specific git commit hashes, indicating the vulnerability is present in recent Linux kernel versions prior to the patch. No CVSS score has been assigned yet. The vulnerability impacts the kernel's integrity and stability, potentially leading to denial of service or kernel crashes if exploited. Since it involves kernel-level concurrency issues, exploitation might require local privileges or crafted network conditions to trigger the race. However, the absence of authentication or user interaction requirements for network interface state changes could increase the attack surface in certain environments.

For European organizations, the impact of CVE-2024-26631 can be significant, especially for those relying heavily on Linux-based infrastructure, including servers, network appliances, and embedded systems that use IPv6 multicast networking. The vulnerability could lead to kernel crashes or instability, resulting in denial of service conditions that disrupt critical services such as telecommunications, cloud computing, and industrial control systems. Organizations operating IPv6-enabled networks with multicast traffic—common in telecom, media streaming, and IoT deployments—are particularly at risk. The data race could be exploited to cause unpredictable kernel behavior, potentially allowing attackers to degrade system availability or cause system reboots. Although no direct privilege escalation or remote code execution is indicated, the instability caused by this race condition can be leveraged as part of a broader attack chain or to disrupt operations. Given the increasing adoption of IPv6 in Europe and the widespread use of Linux in enterprise and government environments, the vulnerability poses a tangible risk to network reliability and service continuity. Additionally, critical infrastructure sectors regulated under EU cybersecurity directives (e.g., NIS2) must consider this vulnerability in their risk assessments and incident response planning.

To mitigate CVE-2024-26631, European organizations should: 1) Apply the official Linux kernel patches that introduce proper locking around multicast interface count updates as soon as they become available from trusted Linux distribution vendors or upstream kernel sources. 2) For environments where immediate patching is not feasible, consider temporarily disabling IPv6 multicast features if they are not essential, to reduce the attack surface. 3) Monitor kernel logs and system stability metrics for signs of race conditions or unexpected network interface state changes that could indicate exploitation attempts. 4) Employ kernel hardening techniques such as Kernel Address Sanitizer (KASAN) and Kernel Concurrency Sanitizer (KCSAN) in testing environments to detect similar concurrency issues proactively. 5) Maintain strict network segmentation and access controls to limit exposure of vulnerable systems to untrusted networks, especially where multicast traffic is involved. 6) Incorporate this vulnerability into vulnerability management and patching workflows, prioritizing Linux systems that handle IPv6 multicast traffic or are critical to network infrastructure. 7) Engage with Linux distribution security advisories and subscribe to relevant security mailing lists to receive timely updates and patches.