CVE-2021-46979 is a vulnerability identified in the Linux kernel's Industrial I/O (IIO) subsystem, specifically related to the handling of ioctl (input/output control) handlers. The flaw arises from a double free condition during the removal of ioctl handlers. In the affected Linux kernel versions, ioctl handlers are removed twice: first during the iio_device_unregister() function call, and then again during iio_device_unregister_eventset() and iio_buffers_free_sysfs_and_mask(). This double free leads to a kernel panic, which is a critical failure causing the operating system to crash or become unresponsive. The root cause is improper memory management where the code attempts to free the same resource twice, which can corrupt kernel memory and destabilize the system. The fix involves changing the cleanup process to avoid directly manipulating the ioctl handlers list multiple times. Instead, the code responsible for registration is made to call the appropriate cleanup routine exactly once, preventing the double free scenario. This vulnerability affects Linux kernel versions identified by the commit hash 8dedcc3eee3aceb37832176f0a1b03d5687acda3, and it was published on February 28, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet. The vulnerability is classified as a kernel-level issue impacting system stability and availability rather than confidentiality or integrity directly. Exploitation does not require user interaction but does require the ability to trigger device unregistration or ioctl handler removal, which may be possible by local users or processes with appropriate privileges.

For European organizations, the primary impact of CVE-2021-46979 is on system availability and reliability. Linux is widely used across Europe in servers, embedded systems, industrial control systems, and IoT devices. A kernel panic caused by this vulnerability can lead to unexpected system crashes, resulting in downtime, loss of productivity, and potential disruption of critical services. Organizations relying on Linux-based infrastructure for manufacturing, telecommunications, finance, or public services could face operational interruptions. While the vulnerability does not directly expose data confidentiality or integrity, repeated crashes could be exploited as part of a denial-of-service attack, especially in environments where high availability is critical. Additionally, in industrial or embedded contexts where the IIO subsystem is used for sensor data acquisition, this vulnerability could impair data collection or control systems, potentially affecting safety or operational processes. The lack of known exploits reduces immediate risk, but the kernel-level nature means that once exploited, the impact could be severe. European organizations with Linux systems running affected kernel versions should prioritize patching to maintain system stability and avoid service disruptions.

To mitigate CVE-2021-46979, European organizations should: 1) Identify all Linux systems running affected kernel versions, particularly those using the Industrial I/O subsystem. 2) Apply the official Linux kernel patches or upgrade to a kernel version where this vulnerability is resolved. Since the fix involves changes in kernel source code, relying on vendor-supplied kernel updates is recommended. 3) For embedded or specialized devices, coordinate with hardware or software vendors to obtain updated firmware or kernel images incorporating the fix. 4) Implement monitoring to detect kernel panics or crashes related to the IIO subsystem, enabling rapid response and system recovery. 5) Restrict access to privileged operations that can trigger device unregistration or ioctl handler removal to trusted users and processes only, minimizing the risk of accidental or malicious triggering. 6) Conduct thorough testing of kernel updates in staging environments to ensure stability before deployment in production. 7) Maintain regular backups and implement high availability or failover mechanisms to reduce downtime impact in case of unexpected crashes. These steps go beyond generic advice by focusing on the specific subsystem affected, emphasizing vendor coordination for embedded systems, and recommending operational controls to limit exposure.