CVE-2021-46956 is a vulnerability identified in the Linux kernel specifically related to the virtiofs component, which is used for sharing filesystems between host and guest in virtualized environments using QEMU. The vulnerability arises from a memory leak in the virtio_fs_probe() function when the same tag is accidentally passed twice to QEMU. This causes the kernel memory leak detector (kmemleak) to report unreferenced objects, indicating that allocated memory is not properly freed. The error logs show a failure in probing the virtio device with an error code -17, which corresponds to EEXIST (File exists), caused by the duplicated tag. The backtrace reveals that the issue occurs during device probing and driver attachment phases in the kernel initialization process. Although this vulnerability does not appear to allow direct code execution or privilege escalation, the memory leak could lead to resource exhaustion over time, potentially degrading system performance or causing denial of service in environments heavily relying on virtiofs for filesystem sharing. The vulnerability affects Linux kernel versions identified by the commit hash a62a8ef9d97da23762a588592c8b8eb50a8deb6a and was published on February 27, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, especially those utilizing Linux-based virtualization infrastructures with QEMU and virtiofs for efficient file sharing between host and guest systems, this vulnerability could lead to gradual memory leaks that degrade system stability and availability. Data confidentiality and integrity are unlikely to be directly impacted by this vulnerability since it does not enable arbitrary code execution or privilege escalation. However, the memory leak could cause denial of service conditions by exhausting kernel memory resources, particularly in large-scale virtualized environments such as cloud service providers, data centers, and enterprises running containerized or virtualized workloads. This could result in downtime or degraded performance of critical services. Organizations relying on Linux virtualization for critical infrastructure or sensitive workloads should consider this vulnerability a risk to operational continuity. Given the absence of known exploits, the immediate risk is moderate, but unpatched systems remain vulnerable to potential future exploitation or accidental system failures.

1. Apply the official Linux kernel patches that address this memory leak in the virtiofs component as soon as they become available. Monitor Linux kernel mailing lists and vendor advisories for updates. 2. Review and audit QEMU configurations to ensure that unique tags are used for virtiofs mounts to prevent accidental duplication, which triggers the memory leak. 3. Implement monitoring of kernel memory usage and kmemleak logs in virtualized hosts to detect early signs of memory leaks related to virtiofs. 4. For environments where patching is delayed, consider disabling virtiofs if it is not critical to operations or replacing it with alternative file sharing mechanisms temporarily. 5. Conduct regular system and kernel updates as part of a robust patch management program to minimize exposure to known vulnerabilities. 6. Engage with Linux distribution vendors for backported patches if using long-term support kernels to ensure timely remediation without full kernel upgrades.