CVE-2024-26686 is a vulnerability identified in the Linux kernel related to the handling of task statistics gathering in the proc filesystem interface, specifically within the do_task_stat() function. The root cause lies in the improper locking mechanism when multiple CPUs (NR_CPUS) concurrently invoke do_task_stat() on a process with many threads (NR_THREADS). The function lock_task_sighand(), which is called during this operation, can cause a hard lockup by spinning excessively with interrupts disabled. This spinlock behavior results in a CPU deadlock scenario, where the system becomes unresponsive due to the kernel waiting indefinitely while interrupts are disabled, severely impacting system availability. The vulnerability arises because the original code used the siglock to protect the critical section, but this was insufficient under high concurrency. The fix involves modifying do_task_stat() to use sig->stats_lock to gather thread and child process statistics outside the siglock-protected section, allowing the code to run lockless in most cases and preventing the excessive spinning. This vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and likely other versions prior to the patch. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The vulnerability primarily threatens system stability and availability rather than confidentiality or integrity, as it can cause system-wide hard lockups under specific high-load conditions involving multi-threaded processes and multi-CPU systems.

For European organizations, this vulnerability poses a significant risk to the availability and reliability of Linux-based systems, which are widely used in enterprise servers, cloud infrastructure, and critical industrial control systems. Systems running multi-threaded applications on multi-core processors are particularly vulnerable to hard lockups, potentially leading to downtime, service interruptions, and operational disruptions. This can affect sectors such as finance, telecommunications, healthcare, and public administration, where Linux servers are prevalent. The inability to process tasks or respond to system events due to kernel lockups could result in loss of productivity, degraded service quality, and increased operational costs. Additionally, organizations relying on Linux for container orchestration or virtualization may experience cascading failures affecting multiple services. Although no active exploits are known, the vulnerability's nature means that attackers or even benign workloads triggering this condition could cause denial of service. The impact is thus primarily on system availability and operational continuity rather than data confidentiality or integrity.

European organizations should prioritize patching affected Linux kernel versions as soon as updates become available from trusted sources or Linux distributions. Since the vulnerability involves kernel-level locking, updating to a kernel version that includes the fix (using sig->stats_lock in do_task_stat()) is critical. In environments where immediate patching is not feasible, organizations can mitigate risk by limiting the concurrency of threads and processes that invoke do_task_stat(), for example by controlling workload concurrency or isolating high-thread-count processes on dedicated CPUs. Monitoring system logs for symptoms of lockups or excessive spinning in kernel threads can provide early warning signs. Additionally, implementing robust system monitoring and automated recovery mechanisms (such as watchdog timers and kernel crash dumps) can reduce downtime impact. For critical systems, consider using kernel live patching technologies where supported to apply fixes without rebooting. Finally, organizations should review and harden their incident response plans to quickly address potential denial-of-service conditions caused by this vulnerability.