CVE-2024-26992 is a vulnerability in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem related to the handling of adaptive Precise Event-Based Sampling (PEBS) on x86 architectures. Adaptive PEBS is a performance monitoring feature that allows detailed tracing of CPU events. The vulnerability arises because KVM's implementation of adaptive PEBS is fundamentally flawed and exposes sensitive host kernel information to guest virtual machines (VMs). Specifically, several bugs cause improper handling of performance monitoring registers and counters, leading to leakage of host Last Branch Records (LBRs) to guest VMs. This leakage can reveal host kernel addresses, which are critical for attackers aiming to bypass kernel address space layout randomization (KASLR) and escalate privileges. The key technical issues include: 1) KVM failing to manage the upper 32 bits of IA32_FIXED_CTR_CTRL MSR correctly, causing truncation and misconfiguration of fixed counters; 2) KVM always enabling adaptive PEBS records regardless of guest requests, leading to unintended exposure; 3) the Linux perf subsystem not properly disabling adaptive PEBS counters, which results in them being enabled even when not desired; 4) adaptive PEBS potentially bypassing event filters set by the host, allowing unauthorized data collection; and 5) KVM not sanitizing LBR MSRs on vCPU entry, enabling guests to read host LBR data. Due to the complexity and severity of these issues, the immediate mitigation is to disable adaptive PEBS support in KVM entirely. This fix prevents the leakage but breaks live migration of VMs using adaptive PEBS. The vulnerability is not currently known to be exploited in the wild, and no CVSS score has been assigned yet. However, the impact on confidentiality and potential for privilege escalation is significant. The vulnerability affects Linux kernel versions containing the specified commit hashes and is relevant to environments running KVM virtualization on x86 platforms with adaptive PEBS enabled.

For European organizations, especially those relying on Linux-based virtualization infrastructures using KVM on x86 hardware, this vulnerability poses a serious confidentiality risk. The leakage of host kernel addresses to guest VMs can facilitate advanced attacks such as kernel-level exploits, privilege escalation, and escape from virtualized environments. This is particularly critical for cloud service providers, data centers, and enterprises running multi-tenant virtualized workloads, where isolation between guests and hosts is paramount. The inability to trust the isolation boundary could lead to unauthorized access to sensitive data or disruption of critical services. Additionally, the disabling of adaptive PEBS to mitigate the issue may impact performance monitoring and debugging capabilities, potentially complicating incident response and system optimization efforts. The breakage of live migration functionality could affect operational flexibility and disaster recovery plans, especially for organizations with distributed data centers or hybrid cloud deployments. Overall, the vulnerability undermines the security guarantees of virtualization platforms widely used in European IT infrastructures, increasing the risk profile for critical sectors such as finance, healthcare, telecommunications, and government.

1. Immediately apply the Linux kernel patches that disable adaptive PEBS support in KVM to prevent leakage of host LBRs to guest VMs. 2. Audit virtualization environments to identify any use of adaptive PEBS features and disable them at the hypervisor level. 3. Review and update virtualization management policies to account for the loss of live migration capabilities when adaptive PEBS is disabled; plan alternative migration or failover strategies. 4. Enhance monitoring for unusual guest VM behavior that might indicate attempts to exploit performance monitoring features. 5. Limit guest VM privileges and restrict access to performance monitoring interfaces where possible to reduce attack surface. 6. Coordinate with hardware and virtualization vendors to track updates and patches related to this vulnerability. 7. For environments requiring detailed performance monitoring, consider alternative tools or configurations that do not rely on adaptive PEBS until a secure implementation is available. 8. Conduct security awareness training for system administrators on the implications of this vulnerability and the importance of timely patching and configuration changes.