CVE-2021-47520 is a use-after-free vulnerability identified in the Linux kernel, specifically within the CAN (Controller Area Network) driver component pch_can. The vulnerability arises in the function pch_can_rx_normal, where after invoking the function netif_receive_skb(skb), the code erroneously dereferences the skb (socket buffer) pointer. Since netif_receive_skb(skb) may consume or free the skb, any subsequent dereference of skb or its aliased memory, such as the can_frame cf, leads to undefined behavior and potential memory corruption. This use-after-free condition can cause system instability, crashes, or potentially be leveraged for arbitrary code execution if exploited. The root cause is a sequencing error in the code, where the dereference of skb occurs immediately after netif_receive_skb(skb) without ensuring skb is still valid. The fix involves reordering the code lines to prevent dereferencing freed memory. This vulnerability affects specific Linux kernel versions identified by commit hashes, indicating it is present in certain kernel builds prior to the patch. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. However, the nature of the vulnerability in a core kernel networking driver suggests a significant security concern, especially for systems utilizing CAN interfaces, which are common in automotive and industrial control environments.

For European organizations, the impact of CVE-2021-47520 can be substantial, particularly for industries relying on Linux-based systems with CAN bus interfaces. This includes automotive manufacturers, industrial automation companies, and critical infrastructure operators who use Linux kernels with the affected CAN driver. Exploitation could lead to kernel crashes, denial of service, or potentially privilege escalation if attackers craft malicious CAN frames or network packets. This could disrupt manufacturing processes, vehicle diagnostics, or control systems, leading to operational downtime and safety risks. Additionally, organizations in sectors such as transportation, energy, and manufacturing in Europe may face compliance and regulatory challenges if such vulnerabilities are exploited. Given the kernel-level nature of the flaw, successful exploitation could compromise system integrity and confidentiality, impacting sensitive operational data and control commands.

To mitigate CVE-2021-47520, European organizations should: 1) Apply the official Linux kernel patches that reorder the code to prevent use-after-free in the pch_can driver as soon as they become available from trusted Linux distributions or kernel maintainers. 2) Identify and inventory all Linux systems using CAN interfaces, particularly those running affected kernel versions, to prioritize patch deployment. 3) Employ kernel hardening techniques such as enabling Kernel Address Space Layout Randomization (KASLR), Kernel Page Table Isolation (KPTI), and other memory protection features to reduce exploitation risk. 4) Restrict access to CAN interfaces and related network subsystems to trusted users and processes only, minimizing attack surface. 5) Monitor system logs and kernel messages for anomalies related to CAN driver activity or crashes that could indicate exploitation attempts. 6) For critical environments, consider isolating CAN network segments and applying network-level filtering to block unauthorized CAN traffic. 7) Maintain an up-to-date incident response plan that includes steps for kernel-level vulnerabilities and potential exploitation scenarios.