CVE-2021-47013 is a use-after-free vulnerability identified in the Linux kernel's network driver code, specifically within the emac_mac_tx_buf_send function. The vulnerability arises due to improper handling of socket buffer (skb) memory during transmission buffer preparation. In detail, the function emac_mac_tx_buf_send calls emac_tx_fill_tpd(.., skb, ..) to fill the transmit packet descriptor. If emac_tx_fill_tpd encounters an error, it frees the skb using dev_kfree_skb(skb). However, after this free operation, the code continues to access the freed skb memory via skb->len in the call to netdev_sent_queue(, skb->len). Since the skb has already been freed, this results in a use-after-free condition, which can lead to undefined behavior including kernel crashes, memory corruption, or potential privilege escalation. The patch for this vulnerability involves storing the skb->len value in a local variable before the potential free and using this stored length value afterward instead of accessing the freed skb structure. This fix prevents the use-after-free by ensuring no access to freed memory occurs after skb is freed. The vulnerability affects specific Linux kernel versions identified by the commit hash b9b17debc69d27cd55e21ee51a5ba7fc50a426cf and was publicly disclosed on February 28, 2024. There are no known exploits in the wild at the time of publication, and no CVSS score has been assigned yet. The vulnerability is rooted in kernel network driver code, which is critical for network packet processing and transmission, making it a significant concern for systems relying on affected Linux kernel versions.

For European organizations, this vulnerability poses a risk primarily to systems running affected Linux kernel versions, especially those deployed in network infrastructure, servers, and embedded devices using the emac network driver. Exploitation could lead to kernel crashes causing denial of service, or potentially allow attackers to execute arbitrary code with kernel privileges if combined with other vulnerabilities or attack vectors. This could compromise confidentiality, integrity, and availability of critical systems. Given the widespread use of Linux in European data centers, cloud environments, telecommunications infrastructure, and industrial control systems, the impact could be substantial if exploited. Disruption of network services or compromise of sensitive data could affect sectors such as finance, healthcare, government, and critical infrastructure. Although no active exploits are known, the presence of a use-after-free in kernel code is a serious security concern that warrants prompt attention to prevent future exploitation attempts.

European organizations should prioritize patching affected Linux kernel versions by applying the official fix that addresses the use-after-free in emac_mac_tx_buf_send. Since the vulnerability is in the kernel network driver, updating to the latest stable kernel release that includes the patch is the most effective mitigation. For systems where immediate patching is not feasible, organizations should consider isolating vulnerable systems from untrusted networks to reduce exposure. Network monitoring for unusual kernel crashes or anomalous network behavior may help detect exploitation attempts. Additionally, employing kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), Kernel Page Table Isolation (KPTI), and enabling security modules like SELinux or AppArmor can reduce exploitation risk. Organizations should also review and restrict user privileges to limit the ability of attackers to trigger the vulnerability. Regular vulnerability scanning and inventory of Linux kernel versions in use will help identify at-risk systems. Finally, maintaining robust incident response plans to quickly address potential exploitation is recommended.