CVE-2021-47616 is a use-after-free (UAF) vulnerability identified in the Linux kernel's RDMA (Remote Direct Memory Access) subsystem, specifically within the rxe (RDMA over Converged Ethernet) driver. The vulnerability arises in the error handling path of the function rxe_qp_from_init(). During this process, the send queue (sq.queue) associated with a queue pair (qp) is freed prematurely. Subsequently, the rxe_create_qp() function decreases the reference count of this object, which leads to the qp cleanup function attempting to free the already freed queue again. This double-free scenario results in a use-after-free condition, which can cause kernel memory corruption, potentially leading to system crashes or arbitrary code execution within kernel space. The fix implemented involves zeroing out the queue pointer after freeing it in rxe_qp_from_init(), preventing the cleanup function from attempting to free the queue a second time. This vulnerability affects Linux kernel versions containing the specified commit hashes and is relevant to systems utilizing RDMA over Ethernet, commonly found in high-performance computing, data centers, and enterprise environments where low-latency, high-throughput networking is critical. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2021-47616 could be significant, especially for those operating data centers, cloud infrastructure, or high-performance computing clusters that leverage RDMA technology for efficient network communication. Exploitation of this vulnerability could allow a local attacker or a malicious process with limited privileges to corrupt kernel memory, potentially escalating privileges to root or causing denial of service through system crashes. This could disrupt critical services, lead to data loss or leakage, and undermine operational continuity. Given the kernel-level nature of the vulnerability, successful exploitation could compromise the confidentiality, integrity, and availability of affected systems. Organizations in sectors such as finance, telecommunications, research institutions, and cloud service providers in Europe, which often rely on Linux-based infrastructure with RDMA capabilities, are particularly at risk. The absence of known exploits suggests limited immediate threat, but the vulnerability's presence in widely deployed Linux kernels necessitates proactive mitigation to prevent future exploitation.

To mitigate CVE-2021-47616, European organizations should: 1) Apply the latest Linux kernel patches that address this vulnerability as soon as they become available from their Linux distribution vendors or upstream kernel sources. 2) Audit and inventory systems to identify those utilizing RDMA over Ethernet (rxe driver) and prioritize patching on these hosts. 3) Implement strict access controls and monitoring to limit unprivileged user access to systems with RDMA capabilities, reducing the attack surface. 4) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), Kernel Page Table Isolation (KPTI), and use of security modules like SELinux or AppArmor to mitigate exploitation impact. 5) Monitor system logs and kernel crash reports for anomalies that could indicate exploitation attempts. 6) Consider disabling the rxe driver or RDMA functionality on systems where it is not required to eliminate exposure. These steps go beyond generic advice by focusing on targeted patching, access control, and system hardening specific to the affected subsystem.