CVE-2021-47367 is a medium-severity vulnerability in the Linux kernel's virtio-net driver, which is responsible for network virtualization. The issue arises during the construction of socket buffers (skb) in "big mode," where the kernel attempts to optimize memory usage by building skbs if sufficient tailroom is available. However, the vulnerability is due to a failure to release unused memory pages that are chained via a private pointer when operating in big mode. This results in a memory leak of pages, which can degrade system performance over time and potentially lead to resource exhaustion. The vulnerability is classified under CWE-119, indicating a memory management error related to improper handling of memory buffers. The CVSS 3.1 base score is 5.5 (medium), with the vector indicating that the attack requires local access (AV:L), low attack complexity (AC:L), low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), high confidentiality impact (C:H), no integrity impact (I:N), and no availability impact (A:N). Although the vulnerability does not directly allow code execution or privilege escalation, the leakage of memory pages can be exploited by an attacker with local access to degrade system stability or cause denial of service by exhausting kernel memory resources. The fix involves properly releasing the unused pages after building the skb in big mode, preventing the leak. No known exploits are currently reported in the wild, but the vulnerability affects Linux kernel versions identified by the given commit hashes, and any system running affected kernel versions with virtio-net enabled is potentially vulnerable.

For European organizations, the impact of CVE-2021-47367 primarily concerns systems running Linux kernels with the vulnerable virtio-net driver, especially in virtualized environments such as cloud infrastructure, data centers, and enterprise servers. Memory leaks in kernel space can lead to gradual resource exhaustion, causing degraded network performance, system instability, or crashes. This can disrupt critical services, especially in sectors relying heavily on virtualization and containerization, such as finance, telecommunications, healthcare, and government. While the vulnerability does not directly expose data or allow remote code execution, the high confidentiality impact rating suggests that memory leakage could potentially expose sensitive kernel memory contents under certain conditions. The requirement for local access and low privileges means that attackers would need some level of access to the system, such as through compromised user accounts or insider threats. European organizations with multi-tenant cloud environments or virtualized infrastructure should be particularly vigilant, as the vulnerability could be exploited to impact service availability or confidentiality within shared environments.

To mitigate CVE-2021-47367, European organizations should: 1) Apply the latest Linux kernel patches that address the memory leak in the virtio-net driver as soon as they become available from their Linux distribution vendors or upstream kernel sources. 2) Audit and monitor systems running virtualized workloads using virtio-net for unusual memory usage patterns or kernel resource exhaustion symptoms. 3) Restrict local access to critical systems by enforcing strict access controls, multi-factor authentication, and minimizing the number of users with local login privileges. 4) Employ kernel hardening and runtime security tools that can detect anomalous kernel memory behavior or leaks. 5) In cloud or virtualized environments, isolate workloads and tenants to limit the impact of potential exploitation. 6) Regularly update and patch virtualization infrastructure components and hypervisors to reduce the attack surface. 7) Conduct security awareness training to reduce the risk of insider threats or credential compromise that could lead to local access exploitation.