CVE-2021-46966 is a vulnerability identified in the Linux kernel's ACPI (Advanced Configuration and Power Interface) subsystem, specifically within the custom_method implementation. The issue stems from a use-after-free condition in the cm_write() function. In this function, a buffer (buf) is allocated and freed unconditionally at the end of the function. However, if the requested write count is less than the length of the ACPI table, the buffer is freed prematurely, but subsequent calls to cm_write() still attempt to access this freed buffer, leading to a use-after-free scenario. This type of vulnerability can cause undefined behavior, including potential kernel crashes (denial of service) or memory corruption, which could be leveraged for privilege escalation or arbitrary code execution within the kernel context. The fix involves removing the unconditional kfree(buf) call at the end of the function and setting the buffer pointer to NULL in error paths to prevent further access after freeing. Affected Linux kernel versions include multiple commits and branches, indicating that this vulnerability spans several kernel versions. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The vulnerability was published on February 27, 2024, and is recognized by the Linux project and CISA as a security issue requiring attention.

For European organizations, this vulnerability poses a significant risk primarily to systems running vulnerable Linux kernel versions, which are common in servers, cloud infrastructure, embedded devices, and IoT deployments. Exploitation could lead to kernel crashes causing denial of service, impacting availability of critical services. More severe exploitation could allow attackers to execute arbitrary code with kernel privileges, potentially leading to full system compromise, data breaches, or lateral movement within networks. Given the widespread use of Linux in European data centers, governmental institutions, and enterprises, the impact could be substantial if exploited. Critical infrastructure relying on Linux-based systems, such as telecommunications, energy, and transportation sectors, could face operational disruptions. Additionally, the vulnerability could be leveraged in targeted attacks against high-value assets or supply chain components. The absence of known exploits currently reduces immediate risk, but the potential for future weaponization necessitates proactive mitigation.

European organizations should promptly identify and inventory Linux systems running affected kernel versions. They should apply the official patches or kernel updates provided by their Linux distribution vendors as soon as they become available. In environments where immediate patching is not feasible, organizations should implement strict access controls to limit untrusted user or process interactions with ACPI interfaces and kernel modules. Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), and enable security modules like SELinux or AppArmor to reduce exploitation likelihood. Monitoring kernel logs for unusual crashes or memory errors related to ACPI can provide early detection of exploitation attempts. For critical systems, consider isolating vulnerable hosts or using virtualization/containerization to contain potential compromises. Additionally, maintain up-to-date backups and incident response plans tailored to kernel-level compromises. Collaboration with Linux distribution maintainers and security communities will ensure timely awareness of patches and exploit developments.