CVE-2024-56739 is a vulnerability identified in the Linux kernel's Real-Time Clock (RTC) subsystem. Specifically, the issue arises in the rtc_timer_do_work() function, which handles periodic timer events related to the RTC hardware. The vulnerability occurs because the function does not properly verify the success of the __rtc_read_time() call. If __rtc_read_time() fails, the rtc_time structure (struct rtc_time tm) may contain uninitialized or invalid date/time data. Subsequently, when rtc_tm_to_ktime() converts this faulty rtc_time structure to a kernel time value, it can produce an abnormally large value, potentially KTIME_MAX. This erroneous large time value causes timers in the rtc->timerqueue to expire repeatedly and rapidly, leading to a kernel softlockup—a state where the kernel becomes unresponsive due to excessive CPU time spent handling the timer events. This vulnerability affects multiple versions of the Linux kernel (as indicated by the repeated commit hash references), and it was publicly disclosed on December 29, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet. The root cause is a lack of error checking after reading RTC time, which leads to corrupted timer data and system instability. This vulnerability could impact any Linux system using the affected kernel versions and relying on RTC timers, including servers, embedded devices, and desktops.

For European organizations, the impact of CVE-2024-56739 could be significant, especially for those relying on Linux-based infrastructure for critical operations. The vulnerability can cause kernel softlockups, resulting in system hangs or crashes that disrupt availability. This can affect servers running critical applications, network devices, industrial control systems, and embedded devices that depend on accurate RTC timers. The unavailability of affected systems could lead to operational downtime, loss of productivity, and potential disruption of services. While this vulnerability does not directly expose confidentiality or integrity risks, the denial of service caused by kernel softlockups can indirectly impact business continuity and service reliability. Organizations in sectors such as finance, healthcare, telecommunications, and manufacturing—where Linux is widely deployed—may face operational risks if timely patching is not performed. Additionally, embedded Linux devices used in IoT and industrial environments across Europe could be vulnerable, potentially affecting critical infrastructure components.

To mitigate CVE-2024-56739, European organizations should: 1) Apply the official Linux kernel patches that address the error checking in rtc_timer_do_work() as soon as they become available from trusted sources or Linux distributions. 2) For environments where immediate patching is not feasible, consider temporarily disabling RTC periodic timers if possible, or isolate affected systems to reduce impact. 3) Monitor system logs for kernel softlockup warnings or abnormal RTC timer behavior to detect potential exploitation attempts or system instability. 4) Implement robust system monitoring and alerting to quickly identify and respond to kernel hangs or crashes. 5) For embedded and IoT devices running custom Linux kernels, coordinate with vendors or internal development teams to backport the fix. 6) Maintain an inventory of Linux kernel versions in use across the organization to prioritize patching efforts. 7) Conduct thorough testing of patches in staging environments to ensure stability before deployment in production. These steps go beyond generic advice by focusing on RTC timer-specific mitigations and operational monitoring tailored to this vulnerability.