CVE-2024-38630 is a use-after-free vulnerability identified in the Linux kernel's watchdog subsystem, specifically within the cpu5wdt driver module. The vulnerability arises during the removal of the cpu5wdt module, where the original code uses the del_timer() function to deactivate a timer. However, del_timer() does not guarantee that the timer handler has completed execution if it is currently running; it simply returns immediately if the handler is active. This creates a race condition where the port region, which the timer handler accesses, can be released prematurely by release_region(). Subsequently, the timer handler function cpu5wdt_trigger() may attempt to write to this now-released port region using outb(), resulting in a use-after-free condition. This memory safety flaw can lead to undefined behavior, including kernel crashes (denial of service) or potential escalation of privileges if exploited. The fix involves replacing del_timer() with timer_shutdown_sync(), which ensures the timer handler has fully completed before the port region is released, thereby eliminating the race condition and preventing the use-after-free scenario. This vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and was publicly disclosed on June 21, 2024. There are no known exploits in the wild at this time.

For European organizations, this vulnerability poses a moderate to high risk depending on their use of Linux systems with the affected cpu5wdt watchdog driver. The watchdog subsystem is critical for system stability, often used in embedded systems, servers, and industrial control environments to detect and recover from system hangs. Exploitation could lead to kernel crashes causing denial of service, impacting availability of critical services. In worst cases, an attacker with local access might leverage this flaw to execute arbitrary code in kernel context, potentially escalating privileges and compromising system integrity and confidentiality. Organizations relying on Linux-based infrastructure in sectors such as manufacturing, telecommunications, and critical infrastructure could face operational disruptions. Additionally, the vulnerability could be leveraged as a foothold for lateral movement within networks if exploited by insiders or through compromised accounts. Although no public exploits exist yet, the presence of a use-after-free in kernel code is a serious concern that warrants prompt attention.

European organizations should prioritize applying the official Linux kernel patch that replaces del_timer() with timer_shutdown_sync() in the cpu5wdt driver to ensure safe timer handler shutdown. System administrators should verify kernel versions and update to patched releases as soon as they become available from their Linux distribution vendors. For environments where immediate patching is not feasible, disabling or unloading the cpu5wdt module can reduce exposure, provided this does not impact critical functionality. Organizations should also implement strict access controls to limit local user privileges, as exploitation requires local code execution. Monitoring kernel logs for unusual watchdog timer activity or crashes can help detect attempted exploitation. Incorporating kernel integrity monitoring and leveraging security modules such as SELinux or AppArmor can further reduce risk. Finally, maintaining robust incident response plans for kernel-level compromises is advisable.