CVE-2021-47669 is a high-severity use-after-free vulnerability identified in the Linux kernel's CAN (Controller Area Network) subsystem, specifically within the vxcan driver implementation. The vulnerability arises in the vxcan_xmit function where, after invoking netif_rx_ni(skb), the code erroneously continues to dereference the socket buffer (skb). This is unsafe because netif_rx_ni() passes skb to the network stack and may free or otherwise invalidate it, making any subsequent access a use-after-free condition. The vulnerability specifically involves the canfd_frame structure (cfd), which aliases the skb memory. Accessing cfd after netif_rx_ni() leads to undefined behavior, potentially causing kernel crashes, memory corruption, or arbitrary code execution in kernel context. The underlying weakness is classified as CWE-416 (Use After Free). The CVSS v3.1 base score is 7.8, reflecting a high severity with characteristics: local attack vector (AV:L), low attack complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). No known exploits are currently reported in the wild, but the vulnerability is critical due to the potential for privilege escalation or denial of service on affected Linux systems. The affected versions correspond to a specific Linux kernel commit hash, indicating the vulnerability is present in certain kernel versions prior to the fix. The vulnerability was publicly disclosed on April 17, 2025, and is enriched by CISA, emphasizing its importance.

For European organizations, the impact of CVE-2021-47669 can be significant, especially those relying on Linux-based systems for critical infrastructure, industrial control systems, automotive applications, or embedded devices that utilize the CAN protocol. Exploitation could lead to kernel-level compromise, allowing attackers to execute arbitrary code with elevated privileges, disrupt system availability through crashes, or exfiltrate sensitive information. This is particularly concerning for sectors such as manufacturing, automotive, energy, and transportation, where CAN bus communication is prevalent. The vulnerability's local attack vector means that attackers need some level of access to the system, but given the low privilege requirement and no user interaction needed, insider threats or attackers leveraging other footholds could escalate privileges rapidly. The high impact on confidentiality, integrity, and availability could result in operational disruptions, data breaches, or safety risks in cyber-physical systems. Additionally, Linux's widespread use in European enterprises and public sector organizations increases the potential attack surface.

To mitigate CVE-2021-47669 effectively, European organizations should: 1) Immediately apply the official Linux kernel patches that address the use-after-free in the vxcan driver. Monitor kernel mailing lists and vendor advisories for updated stable releases containing the fix. 2) For systems where patching is delayed, consider disabling the vxcan module if it is not required, to eliminate the attack surface. 3) Implement strict access controls and segmentation to limit local access to systems running vulnerable kernels, reducing the risk of local exploitation. 4) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), and enable security modules like SELinux or AppArmor to restrict kernel module behavior. 5) Monitor system logs and kernel crash reports for signs of exploitation attempts or instability related to CAN subsystem operations. 6) For embedded or automotive environments, coordinate with device manufacturers to ensure firmware updates incorporate the kernel fix. 7) Conduct regular vulnerability assessments and penetration testing focusing on local privilege escalation vectors to detect potential exploitation paths.