CVE-2024-58083 is a high-severity vulnerability in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem. The flaw arises from improper verification of the target virtual CPU (vCPU) state in the function kvm_get_vcpu(). Specifically, the kernel fails to explicitly verify that the target vCPU is fully online before clamping the index used to access it. When an invalid index is provided, the nospec clamping mechanism returns 0, causing KVM to return a reference to vCPU0 instead of NULL. This behavior is problematic because KVM uses an xarray data structure for managing vCPUs, which requires that vCPUs be fully inserted and published before being accessible. If vCPU0 is accessed prematurely and vCPU creation subsequently fails, a use-after-free (UAF) condition can occur when the kernel dereferences the freed vCPU0 pointer. This UAF can lead to memory corruption, potentially allowing privilege escalation or denial of service within the guest or host environment. The vulnerability is rooted in a race condition and improper state management of vCPU objects, and it was introduced as part of a prior fix that attempted to address related race conditions but created an unsolvable teardown problem. The patch for this vulnerability enforces strict verification that vCPU0 is fully online before access, preventing premature dereferencing and allowing the previous workaround to be reverted safely. Although exploitation requires local privileges and a buggy or malicious userspace or guest, the impact on confidentiality, integrity, and availability is high due to the potential for arbitrary code execution or system crashes within virtualized environments. The CVSS 3.1 score is 7.8 (high), reflecting the local attack vector, low complexity, required privileges, and the significant impact on system security.

For European organizations, this vulnerability poses a significant risk especially to those relying heavily on Linux-based virtualization infrastructure, including cloud service providers, data centers, and enterprises using KVM for server virtualization. Exploitation could allow attackers with local access—such as malicious insiders, compromised tenants in multi-tenant environments, or attackers who gain limited access to virtual machines—to escalate privileges or disrupt services. This could lead to data breaches, service outages, or lateral movement within networks. Given the widespread adoption of Linux and KVM in European public and private sectors, including critical infrastructure, finance, and government, the vulnerability could undermine trust in virtualized environments and impact compliance with regulations like GDPR if data confidentiality is compromised. The requirement for local access and the need for buggy or malicious userspace reduces the likelihood of remote exploitation but does not eliminate risk in shared or multi-tenant environments common in Europe’s cloud ecosystems.

European organizations should prioritize patching Linux kernels to versions that include the fix for CVE-2024-58083 as soon as updates are available from their Linux distribution vendors. Beyond patching, organizations should: 1) Restrict and monitor local access to hosts running KVM, enforcing strict access controls and auditing to detect suspicious activity. 2) Harden guest and userspace applications to prevent buggy or malicious behavior that could trigger the vulnerability, including applying security best practices and using security modules like SELinux or AppArmor. 3) Employ runtime security tools that monitor for unusual kernel or KVM behavior indicative of exploitation attempts. 4) In multi-tenant environments, isolate tenants effectively to limit the impact of a compromised guest. 5) Conduct regular security assessments and penetration testing focusing on virtualization layers. 6) Maintain up-to-date incident response plans that include virtualization-specific attack scenarios. These targeted measures go beyond generic advice by focusing on the unique aspects of this vulnerability’s exploitation vector and environment.