CVE-2021-47080 is a vulnerability identified in the Linux kernel's RDMA (Remote Direct Memory Access) core subsystem. The issue arises from improper handling of a user-supplied parameter named user_entry_size, which is used as a denominator in a calculation to determine the number of entries. If a zero value is supplied by the user, it triggers a divide-by-zero error, leading to a kernel panic or crash. The vulnerability manifests as a divide error in the kernel, as demonstrated by the provided kernel stack trace, which shows the failure occurring in the function ib_uverbs_handler_UVERBS_METHOD_QUERY_GID_TABLE. This function is part of the Infiniband user verbs interface, which handles communication between user space and kernel space for RDMA operations. The root cause is the lack of validation on user_entry_size before it is used in division, allowing malicious or malformed input to cause a denial of service (DoS) by crashing the kernel. The vulnerability affects Linux kernel versions including the one referenced (5.13.0-rc1+), and the issue has been publicly disclosed and patched by the Linux project. No known exploits are reported in the wild at this time, and no CVSS score has been assigned. The vulnerability does not require authentication but does require user interaction in the form of issuing specific ioctl calls to the RDMA subsystem. Exploitation results in loss of availability due to kernel crash, but does not directly impact confidentiality or integrity. The vulnerability is technical in nature and specific to systems utilizing RDMA capabilities in the Linux kernel, which are typically found in high-performance computing, data centers, and enterprise environments.

For European organizations, the primary impact of CVE-2021-47080 is the potential for denial of service on Linux systems that utilize RDMA functionality. RDMA is commonly used in data centers, cloud infrastructure, and high-performance computing clusters to enable low-latency, high-throughput networking. Organizations relying on such infrastructure for critical services could experience service interruptions or system downtime if this vulnerability is exploited. While the vulnerability does not allow privilege escalation or data breach directly, the resulting kernel panic could disrupt business operations, affect availability of services, and require system reboots and incident response. This is particularly relevant for sectors such as finance, telecommunications, research institutions, and cloud service providers in Europe that deploy Linux servers with RDMA support. The lack of known exploits reduces immediate risk, but the vulnerability should be addressed promptly to prevent potential future exploitation. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to cause disruption or as a denial-of-service vector against targeted systems.

European organizations should implement the following specific mitigation steps: 1) Apply the official Linux kernel patches that address CVE-2021-47080 as soon as they are available and tested in their environments. 2) If immediate patching is not feasible, restrict access to the RDMA user verbs interface (typically /dev/infiniband/uverbsX devices) by limiting permissions to trusted users and processes only, reducing the attack surface. 3) Monitor system logs and kernel messages for signs of divide-by-zero errors or kernel panics related to RDMA operations to detect potential exploitation attempts. 4) Employ kernel hardening techniques such as Kernel Address Sanitizer (KASAN) and Kernel Page Table Isolation (KPTI) where supported, which may help detect or mitigate kernel memory corruption issues. 5) For environments where RDMA is not required, consider disabling the RDMA kernel modules to eliminate exposure. 6) Incorporate this vulnerability into vulnerability management and incident response plans to ensure timely detection and remediation. 7) Coordinate with Linux distribution vendors for timely updates and advisories related to this vulnerability.