CVE-2024-54683 is a concurrency vulnerability in the Linux kernel's netfilter subsystem, specifically related to the IDLETIMER target used in iptables. The issue arises from a potential deadlock caused by a circular locking dependency between two kernel locks: the list_mutex and the lock protecting the active idletimer entries. The vulnerability manifests when the last iptables rule referencing a given idletimer is deleted concurrently with a read operation on its corresponding sysfs file. This concurrency leads to a circular lock dependency warning and can cause an ABBA deadlock, where two locks are acquired in conflicting orders by different threads, resulting in a kernel hang or freeze. The vulnerability is reproducible by rapidly adding and deleting iptables rules with the IDLETIMER target while simultaneously reading the associated sysfs timer file. The root cause is that the list_mutex is held during the entire teardown process of the idletimer, including the removal of the sysfs file, which itself requires acquiring another lock that depends on list_mutex, thus creating a circular dependency. The fix involves releasing the list_mutex immediately after removing the element from the list, before continuing with the rest of the teardown, thereby breaking the circular lock dependency and preventing the deadlock. This vulnerability affects Linux kernel versions containing the vulnerable commit identified by the hash 0902b469bd25065aa0688c3cee6f11744c817e7c and was publicly disclosed in January 2025. No known exploits are reported in the wild at this time.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with the affected netfilter IDLETIMER functionality enabled and actively used in firewall configurations. The impact is a potential denial of service (DoS) condition caused by kernel deadlocks, which can freeze or crash critical network infrastructure components such as firewalls, routers, or servers that rely on iptables for packet filtering and connection tracking. This could disrupt network availability, impacting business operations, especially in sectors with high dependency on continuous network uptime such as finance, telecommunications, healthcare, and critical infrastructure. While this vulnerability does not directly lead to privilege escalation or data leakage, the resulting DoS could be exploited as part of a broader attack chain to degrade defenses or cause operational disruption. Given that many European organizations use Linux-based systems extensively, including in cloud environments and embedded devices, the scope of affected systems is significant. However, exploitation requires concurrent and rapid manipulation of iptables rules and sysfs reads, which may limit the ease of exploitation to local or privileged users or automated scripts running on the affected host.

To mitigate this vulnerability, organizations should promptly apply the Linux kernel patches that address the circular locking dependency in the netfilter IDLETIMER code. If immediate patching is not feasible, administrators should avoid rapid and concurrent addition and deletion of iptables rules using the IDLETIMER target, especially in automated scripts or management tools. Monitoring for unusual iptables rule changes and sysfs accesses related to xt_idletimer timers can help detect attempts to trigger the deadlock. Additionally, limiting access to privileged accounts that can modify iptables rules and read sysfs files reduces the risk of accidental or malicious exploitation. For critical systems, consider isolating or disabling the IDLETIMER target if it is not essential. Network segmentation and strict access controls can further reduce the attack surface. Finally, maintain up-to-date kernel versions and subscribe to Linux kernel security advisories to ensure timely awareness and response to such vulnerabilities.