CVE-2024-56669 is a high-severity vulnerability affecting the Linux kernel's IOMMU (Input-Output Memory Management Unit) implementation, specifically the VT-d (Intel Virtualization Technology for Directed I/O) component. The vulnerability arises from improper handling of cache tags related to the Address Translation Services (ATS) feature. In the affected kernel versions, cache tags of type CACHE_TAG_DEVTLB are not removed before disabling ATS, which leads to stale cache tags remaining in the system even after the associated domain is freed. This results in a use-after-free condition, a classic memory corruption flaw categorized under CWE-416. The vulnerability manifests particularly when multiple Virtual Functions (VFs) from different Physical Functions (PFs) are passed through to a single user-space process using vfio-pci, a kernel driver that enables safe direct device access to user-space. Exploitation can cause kernel crashes with NULL pointer dereferences, leading to denial of service and potentially allowing an attacker with limited privileges (low-level privileges but no user interaction required) to escalate privileges or execute arbitrary code in kernel context. The root cause is a race condition or ordering issue in the kernel code where cache_tag_unassign_domain() is called after iommu_disable_pci_caps(), instead of before, which the patch corrects. The vulnerability has a CVSS 3.1 base score of 7.8, reflecting its high impact on confidentiality, integrity, and availability, with low attack complexity and requiring only low privileges but no user interaction. No known exploits are currently reported in the wild, but the vulnerability affects Linux kernel versions prior to the fix, which was published on December 27, 2024.

For European organizations, this vulnerability poses a significant risk especially to enterprises and data centers relying on Linux-based virtualization and containerization environments that utilize IOMMU for device passthrough, such as cloud service providers, telecom operators, and financial institutions. Exploitation could lead to kernel crashes causing denial of service, impacting availability of critical services. More critically, the use-after-free condition could be leveraged by attackers to execute arbitrary code in kernel space, potentially leading to privilege escalation and full system compromise. This is particularly concerning for multi-tenant environments where multiple VFs from different PFs are assigned to user-space processes, a common scenario in virtualized infrastructures. Confidentiality of sensitive data could be compromised if attackers gain kernel-level access. The integrity of systems could also be undermined, affecting trustworthiness of operations and data. Given the widespread use of Linux in European critical infrastructure and enterprise environments, the vulnerability could have broad operational and security impacts if left unpatched.

European organizations should prioritize updating their Linux kernels to versions that include the patch fixing CVE-2024-56669. Specifically, ensure that the kernel version is at or beyond the commit where cache_tag_unassign_domain() is moved before iommu_disable_pci_caps(). For environments using vfio-pci for device passthrough, verify that all virtualized workloads are running on patched kernels. Additionally, organizations should audit their use of IOMMU and device passthrough configurations to minimize exposure, such as limiting the number of VFs assigned to single user-space processes and enforcing strict access controls on privileged operations. Employ kernel hardening techniques like Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) to reduce exploitation likelihood. Monitoring kernel logs for Oops or NULL pointer dereference messages related to iommu or vfio subsystems can help detect attempted exploitation. Finally, implement strict privilege separation and minimize the number of users/processes with permissions to manage IOMMU or PCI device passthrough to reduce attack surface.