CVE-2025-37885 is a vulnerability identified in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem, specifically affecting the x86 architecture's handling of Interrupt Remapping Table Entries (IRTEs). The issue arises when the kernel fails to properly reset an IRTE to host control if the new Global System Interrupt (GSI) routing configuration is not postable. In this context, 'postable' refers to the ability to directly deliver interrupts to a virtual CPU (vCPU) using posted MSI (Message Signaled Interrupt) mode. The vulnerability occurs because the kernel updates the IRTE only if the new GSI is an MSI, leaving the IRTE in a state where it continues to post interrupts to a vCPU even when it should not. This dangling IRTE can cause interrupts to be incorrectly delivered to the guest virtual machine. The most severe consequence is a use-after-free condition, which can happen if the virtual machine is torn down but the underlying host IRQ is not freed properly. This can potentially lead to memory corruption, instability, or privilege escalation within the host or guest environments. The vulnerability affects multiple versions of the Linux kernel, as indicated by the repeated affected version hashes, and was publicly disclosed on May 9, 2025. No CVSS score has been assigned yet, and no known exploits are reported in the wild at the time of disclosure. The root cause lies in improper handling of IRTE updates during GSI routing changes, which is critical for maintaining isolation and correct interrupt delivery in virtualized environments using KVM on x86 platforms.

For European organizations, this vulnerability poses a significant risk primarily to those relying on Linux-based virtualization infrastructure, especially in data centers, cloud service providers, and enterprises using KVM for virtual machine management. The incorrect delivery of interrupts can lead to guest VM instability, potential data corruption, and in worst cases, exploitation of use-after-free conditions could allow attackers to execute arbitrary code or escalate privileges on the host system. This undermines the security boundary between host and guest, threatening confidentiality and integrity of sensitive data processed within virtual machines. Organizations running critical workloads on KVM-based virtualized environments, including financial institutions, healthcare providers, and government agencies, could face operational disruptions and data breaches if this vulnerability is exploited. Additionally, the complexity of the vulnerability means that detection and remediation might require specialized knowledge, potentially delaying patch deployment and increasing exposure time. Given the widespread use of Linux and KVM in European IT infrastructure, the impact could be broad, affecting cloud services, private data centers, and hybrid cloud deployments.

To mitigate CVE-2025-37885, European organizations should take the following specific actions: 1) Immediately apply the official Linux kernel patches that address the IRTE reset logic in KVM once they become available. Monitor Linux kernel mailing lists and vendor advisories for patch releases. 2) Conduct an inventory of all systems running KVM on x86 architectures and prioritize patching those hosting critical or sensitive workloads. 3) Implement strict change management and testing procedures for kernel updates to avoid service disruptions. 4) Employ runtime monitoring tools capable of detecting anomalous interrupt behavior or VM instability that could indicate exploitation attempts. 5) Restrict administrative access to hypervisor hosts to minimize the risk of privilege escalation through this vulnerability. 6) Consider isolating critical virtual machines on separate hosts or using additional security layers such as SELinux or AppArmor profiles to limit the impact of potential exploitation. 7) Engage with cloud service providers to ensure their infrastructure is patched and secure if using third-party virtualized environments. 8) Maintain up-to-date backups and incident response plans to quickly recover from any compromise resulting from this vulnerability.