CVE-2024-50115 is a vulnerability identified in the Linux kernel's implementation of nested virtualization using AMD's Secure Virtual Machine (SVM) technology, specifically within the nested SVM (nSVM) code path. The issue arises from improper handling of the CR3 register's lower 5 bits (bits 4:0) when loading Page Directory Pointer Table Entries (PDPTEs) from memory during nested virtualization. According to the AMD Architecture Programmer's Manual (APM) and Software Developer's Manual (SDM), the CR3 register, which points to the base address of the page-directory-pointer table, must be aligned on a 32-byte boundary, meaning the lower 5 bits should be ignored. While the Kernel-based Virtual Machine (KVM) correctly enforces this alignment when loading PDPTRs, the nested SVM flow fails to do so. This discrepancy can lead to an out-of-bounds memory read if the target page is located at the end of a memory slot and the virtual machine monitor (VMM) does not employ guard pages to prevent such access. Although this vulnerability does not appear to allow direct code execution or privilege escalation, the out-of-bounds read could potentially leak sensitive information from adjacent memory regions. The flaw is specific to nested virtualization scenarios on AMD processors using Linux's KVM with nSVM enabled. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The vulnerability affects certain Linux kernel versions identified by specific commit hashes, and it was publicly disclosed on November 5, 2024. The patch involves ignoring the lower 5 bits of the CR3 register during PDPTE loading in the nSVM code path to enforce proper alignment and prevent out-of-bounds memory access.

For European organizations, the impact of CVE-2024-50115 is primarily relevant to environments utilizing nested virtualization on AMD processors with Linux KVM hypervisors. Organizations running cloud infrastructure, virtualized data centers, or development/testing environments that leverage nested virtualization could be exposed. The vulnerability could lead to information disclosure through out-of-bounds memory reads, potentially leaking sensitive data from adjacent memory areas within the host or guest virtual machines. While the risk of direct system compromise or denial of service is low, the confidentiality breach could be significant in environments handling sensitive or regulated data, such as financial institutions, healthcare providers, or government agencies. Additionally, the complexity of nested virtualization means that exploitation requires specific conditions, including the absence of guard pages and the use of nested SVM on AMD hardware, limiting the attack surface. However, given the increasing adoption of virtualization technologies across European enterprises and cloud providers, the vulnerability warrants prompt attention to prevent potential data leakage and maintain compliance with data protection regulations like GDPR.

To mitigate CVE-2024-50115, European organizations should: 1) Apply the latest Linux kernel updates that include the patch fixing the nSVM CR3 alignment issue as soon as they become available. 2) Review and harden virtualization configurations by enabling guard pages or memory protection mechanisms within the VMM to prevent out-of-bounds memory access. 3) Limit the use of nested virtualization where possible, especially on AMD hardware, until patches are applied. 4) Monitor virtualization hosts for unusual memory access patterns or anomalies that could indicate exploitation attempts. 5) For cloud service providers, ensure that tenant isolation mechanisms are robust and that nested virtualization is only enabled when necessary and properly secured. 6) Conduct security audits and penetration testing focused on virtualization layers to identify potential weaknesses related to this vulnerability. 7) Maintain an inventory of AMD-based systems running Linux KVM with nested virtualization enabled to prioritize patch deployment and risk assessment.