CVE-2024-36953 is a medium-severity vulnerability in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem, specifically affecting the ARM64 architecture's virtual Generic Interrupt Controller version 2 (vgic-v2) implementation. The vulnerability arises in the function vgic_v2_parse_attr(), which is responsible for locating a virtual CPU (vCPU) that corresponds to a user-supplied CPUID. When an invalid CPUID is provided, the helper function kvm_get_vcpu_by_id() returns NULL. However, vgic_v2_parse_attr() does not properly handle this NULL return value, leading to potential improper behavior or kernel instability. The flaw is similar to a previously addressed issue in the GICv3 uaccess flow, where failure to validate the vCPU pointer could cause kernel faults. The fix involves adding a check to ensure that kvm_get_vcpu_by_id() returns a valid vCPU pointer before proceeding, and if not, the ioctl call fails gracefully. The vulnerability has a CVSS 3.1 score of 4.4, reflecting a medium severity with local attack vector, low attack complexity, requiring high privileges, no user interaction, unchanged scope, no confidentiality or integrity impact, but with potential impact on availability. No known exploits are currently reported in the wild. The affected versions are identified by specific Linux kernel commit hashes, indicating that this issue affects certain recent kernel builds prior to the patch. This vulnerability could lead to denial-of-service conditions or kernel crashes when malformed ioctl calls are made to the KVM subsystem on ARM64 platforms.

For European organizations, the primary impact of CVE-2024-36953 is the potential for denial-of-service (DoS) attacks against virtualized environments running on ARM64-based Linux systems. Organizations utilizing ARM64 servers or edge devices with KVM virtualization could experience kernel crashes or system instability if an attacker with high privileges crafts malicious ioctl calls exploiting this vulnerability. While the vulnerability does not compromise confidentiality or integrity, availability disruptions could affect critical services, especially in sectors relying on ARM64 infrastructure such as telecommunications, cloud providers, and IoT deployments. Given the requirement for high privileges and local access, the threat is more relevant for insider threats or attackers who have already gained elevated access. European data centers and enterprises adopting ARM64 architectures for energy efficiency or performance reasons should be aware of this risk. The absence of known exploits reduces immediate risk, but timely patching is important to prevent potential future exploitation.

To mitigate CVE-2024-36953, European organizations should: 1) Identify all ARM64 Linux systems running KVM virtualization and verify kernel versions against the patched commits. 2) Apply the latest Linux kernel updates or backported patches that address this vulnerability as soon as they become available from trusted Linux distributions or vendors. 3) Restrict high-privilege access to KVM ioctl interfaces to trusted administrators only, minimizing the risk of local exploitation. 4) Implement monitoring and alerting for unusual or malformed ioctl calls targeting the KVM subsystem to detect potential exploitation attempts early. 5) For environments where immediate patching is not feasible, consider disabling or limiting KVM usage on ARM64 hosts until updates can be applied. 6) Maintain strict access controls and audit logs for privileged users to detect and respond to insider threats. These steps go beyond generic advice by focusing on ARM64-specific KVM usage and emphasizing access control and monitoring tailored to the vulnerability's exploitation vector.