CVE-2021-47236 is a vulnerability identified in the Linux kernel's USB networking subsystem, specifically within the cdc_eem driver which handles Ethernet Emulation Model (EEM) USB network devices. The flaw arises during the transmission process of network packets (skb - socket buffers) over USB. When the usbnet driver attempts to transmit a packet, it calls eem_tx_fixup() to perform necessary adjustments to the skb. If the skb_copy_expand() function, which attempts to create a larger copy of the skb, fails and returns NULL, the original skb is not freed properly. This results in a memory leak because usbnet_start_xmit() does not get the opportunity to free the original skb after the failure. The patch fixes this by ensuring the original skb is freed immediately in eem_tx_fixup() before checking the clone status, preventing the leak. Although this vulnerability does not directly lead to code execution or privilege escalation, the memory leak can degrade system stability and potentially lead to denial of service (DoS) conditions over time, especially on systems with heavy USB network traffic. The vulnerability affects Linux kernel versions containing the specified commit hash and was published on May 21, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, the primary impact of CVE-2021-47236 lies in potential system reliability and availability issues. Organizations relying on Linux-based systems with USB network interfaces using the cdc_eem driver—common in embedded devices, industrial control systems, or specialized networking equipment—may experience memory leaks leading to resource exhaustion. This could cause network disruptions or system crashes, impacting critical infrastructure, manufacturing environments, or enterprise networks. While the vulnerability does not directly compromise confidentiality or integrity, the resulting denial of service could interrupt business operations or critical services. Given the widespread use of Linux in European data centers, telecommunications, and industrial sectors, unpatched systems could face increased maintenance overhead and risk of outages. However, the absence of known exploits and the requirement for specific USB network configurations somewhat limit the immediate threat scope.

European organizations should prioritize patching Linux kernel versions affected by this vulnerability by applying the official fix that ensures proper skb memory management in the cdc_eem driver. System administrators should audit their environments to identify devices and systems utilizing USB networking with the cdc_eem driver, particularly embedded or industrial systems that may not receive regular updates. For systems where patching is delayed, monitoring USB network traffic and system memory usage can help detect abnormal resource consumption indicative of the leak. Additionally, implementing strict USB device control policies can reduce exposure by limiting the use of USB network devices to trusted hardware. Network segmentation and redundancy can mitigate potential service disruptions caused by DoS conditions. Finally, maintaining up-to-date kernel versions and subscribing to Linux security advisories will ensure timely awareness and response to similar vulnerabilities.