CVE-2021-47076 is a vulnerability identified in the Linux kernel's RDMA (Remote Direct Memory Access) subsystem, specifically within the RXE (RDMA over Converged Ethernet) driver. The flaw arises due to improper handling of Work Queue Element (WQE) status updates during LOCAL_WRITE failures when an invalid local key (lkey) is supplied in atomic operations. The RXE driver fails to update the WQE status correctly, which leads to a kernel panic—a critical system crash—when an atomic operation is attempted with an explicitly incorrect lkey. This vulnerability is rooted in the rxe_completer function, where the error handling for invalid lkeys is insufficient, causing the kernel to dereference invalid memory or enter an inconsistent state. The provided kernel panic trace indicates that the issue manifests during the processing of RDMA atomic operations, which are used for high-performance, low-latency memory access in networked environments. The vulnerability affects Linux kernel versions prior to the patch and is particularly relevant for systems utilizing RDMA over Ethernet, commonly found in high-performance computing clusters, data centers, and enterprise environments that require fast inter-node communication. No known exploits are reported in the wild, and no CVSS score has been assigned yet. The vulnerability was published on March 1, 2024, and is confirmed by the Linux project with enriched information from CISA. The root cause is a missing update of WQE status on LOCAL_WRITE failures, which can be triggered remotely if an attacker can send crafted RDMA atomic operations with invalid lkeys, leading to denial of service via kernel panic.

For European organizations, the impact of CVE-2021-47076 can be significant in environments where Linux servers are deployed with RDMA over Converged Ethernet capabilities. This includes data centers, cloud service providers, research institutions, and enterprises relying on high-performance computing clusters. The primary impact is a denial of service (DoS) condition caused by kernel panics, which can disrupt critical services, degrade system availability, and potentially cause cascading failures in clustered environments. While this vulnerability does not appear to allow privilege escalation or remote code execution directly, the forced system crashes can interrupt business operations, leading to downtime and potential data processing delays. Organizations in sectors such as finance, telecommunications, scientific research, and cloud infrastructure providers in Europe could face operational disruptions if their Linux systems with RDMA are targeted. Additionally, the complexity of RDMA deployments means that recovery from such crashes might require manual intervention, increasing operational costs and response times. Since no known exploits are in the wild, the immediate risk is moderate, but the presence of this vulnerability in critical infrastructure components necessitates prompt mitigation to avoid potential exploitation.

To mitigate CVE-2021-47076, European organizations should: 1) Apply the latest Linux kernel patches that address this vulnerability as soon as they become available from trusted sources or Linux distributions. 2) For environments where immediate patching is not feasible, consider disabling the RXE driver or RDMA over Ethernet functionality if it is not essential to operations, thereby eliminating the attack surface. 3) Implement strict network segmentation and access controls to limit exposure of RDMA-capable interfaces to untrusted or external networks, reducing the likelihood of malicious atomic operation injections. 4) Monitor kernel logs and system behavior for signs of unexpected kernel panics or RDMA subsystem errors, enabling early detection of potential exploitation attempts. 5) Engage with hardware and software vendors to ensure compatibility and support for patched kernels, especially in complex HPC or data center environments. 6) Conduct thorough testing of RDMA-dependent applications post-patching to verify stability and performance, ensuring that mitigations do not adversely affect critical workloads. These steps go beyond generic advice by focusing on the specific RDMA subsystem and operational considerations unique to affected Linux environments.