CVE-2021-47137 is a high-severity vulnerability identified in the Linux kernel, specifically within the network driver code for Lantiq devices. The issue arises in the handling of the RX (receive) ring buffer, which is responsible for managing incoming network packets. When the kernel attempts to allocate memory or perform DMA (Direct Memory Access) mapping for incoming packets, failure in these operations can cause an invalid address to be programmed into the RX descriptor. This improper handling leads to memory corruption, as the kernel may access or overwrite unintended memory regions. The root cause is that upon memory allocation or DMA mapping failure, the driver does not properly reuse the previous socket buffer (skb) and mapping, nor does it correctly drop the problematic packet. The patch for this vulnerability modifies the driver to increment the RX drop counter and reuse the previous skb and mapping when allocation fails, preventing the invalid descriptor programming and subsequent memory corruption. The vulnerability is tracked under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that improper resource management leads to this unsafe state. The CVSS v3.1 base score is 7.8, reflecting high severity, with attack vector Local (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. The vulnerability affects specific Linux kernel versions containing the vulnerable Lantiq network driver code prior to the patch.

For European organizations, this vulnerability poses a significant risk particularly to those using Linux-based systems with Lantiq network hardware or embedded devices relying on this driver. The memory corruption can lead to kernel crashes (denial of service), potential privilege escalation, or arbitrary code execution within the kernel context, threatening system confidentiality, integrity, and availability. Critical infrastructure providers, telecommunications companies, and enterprises deploying Linux in network appliances or IoT devices with Lantiq components are at heightened risk. Exploitation could disrupt network operations, cause service outages, or enable attackers to gain deeper system access. Given the local attack vector, attackers would need some level of access to the affected system, but the low privilege requirement means that even non-administrative users or compromised accounts could exploit this flaw. The lack of user interaction requirement further increases risk in multi-user environments. The impact is amplified in environments where patching is slow or where embedded devices have limited update capabilities, common in industrial or telecom sectors across Europe.

European organizations should prioritize applying the official Linux kernel patches that address this vulnerability, ensuring that the Lantiq network driver is updated to the fixed version. For embedded or specialized devices, coordinate with hardware vendors or device manufacturers to obtain firmware updates incorporating the patch. Network administrators should audit systems to identify devices using Lantiq drivers and isolate or restrict access to these systems to trusted users only, minimizing local attack opportunities. Implement strict access controls and monitoring on systems with Lantiq hardware to detect unusual activity that might indicate exploitation attempts. Additionally, consider deploying kernel hardening techniques such as memory protection features (e.g., Kernel Address Space Layout Randomization - KASLR, and Kernel Page Table Isolation - KPTI) to reduce exploitation success. Regularly review and update incident response plans to include scenarios involving kernel-level memory corruption vulnerabilities. Finally, maintain up-to-date inventories of Linux kernel versions and hardware components to facilitate rapid vulnerability assessment and remediation.