CVE-2021-47668 is a high-severity use-after-free vulnerability in the Linux kernel's Controller Area Network (CAN) subsystem, specifically within the can_restart function. The vulnerability arises due to unsafe dereferencing of the socket buffer (skb) after a call to netif_rx_ni(skb). In this context, the can_frame structure (cf), which aliases the skb memory, is accessed after netif_rx_ni() has been invoked. This leads to a use-after-free condition because netif_rx_ni() may free or otherwise invalidate the skb memory, making subsequent access unsafe and potentially exploitable. The problematic code pattern involves updating network statistics (stats->rx_bytes += cf->len) after the skb has been passed to netif_rx_ni(). The fix involves reordering these operations to ensure that the cf data is accessed before the skb is handed off, thus preventing dereferencing freed memory. This vulnerability is categorized under CWE-416 (Use After Free), which can lead to arbitrary code execution, privilege escalation, or denial of service if exploited. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and requiring low privileges but no user interaction. No known exploits are currently reported in the wild. The vulnerability affects specific Linux kernel versions identified by commit hashes, indicating it is present in certain kernel builds prior to the patch. Given the Linux kernel's widespread use in servers, embedded systems, and network devices, this vulnerability poses a significant risk if exploited, especially in environments utilizing CAN interfaces or related networking stacks.

For European organizations, the impact of CVE-2021-47668 can be substantial, particularly for industries relying on Linux-based systems with CAN bus interfaces, such as automotive manufacturers, industrial automation, telecommunications, and critical infrastructure operators. Exploitation could allow attackers with low privileges to execute arbitrary code or cause denial of service, potentially disrupting operations or compromising sensitive data. Given the Linux kernel's prevalence in servers, cloud infrastructure, and IoT devices across Europe, the vulnerability could be leveraged to pivot within networks or escalate privileges. The high confidentiality, integrity, and availability impacts mean that data breaches, system outages, or control system manipulations are plausible outcomes. Although no exploits are known in the wild yet, the vulnerability's nature and severity warrant proactive mitigation to prevent future attacks. European organizations with stringent regulatory requirements (e.g., GDPR) must consider the risk of data exposure or service disruption due to this kernel flaw.

To mitigate CVE-2021-47668, European organizations should: 1) Identify and inventory Linux systems running vulnerable kernel versions, especially those with CAN interfaces or related networking components. 2) Apply the official Linux kernel patches or upgrade to a fixed kernel version as soon as possible to eliminate the use-after-free condition. 3) For embedded or specialized devices where kernel upgrades are challenging, coordinate with vendors for firmware updates or mitigations. 4) Implement strict access controls to limit low-privilege user access to affected systems, reducing the attack surface. 5) Monitor network and system logs for anomalous behavior indicative of exploitation attempts, focusing on CAN subsystem activity. 6) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), and enable security modules like SELinux or AppArmor to contain potential exploits. 7) Conduct penetration testing and vulnerability assessments post-patching to ensure remediation effectiveness. 8) Maintain an incident response plan tailored to kernel-level vulnerabilities to rapidly address any exploitation attempts.