CVE-2021-47167 is a vulnerability identified in the Linux kernel's implementation of the Network File System (NFS), specifically within the __nfs_pageio_add_request() function. The issue arises due to improper handling of the mirror array contents during error cleanup in nfs_pageio_error_cleanup(). The vulnerability manifests as an 'Oopsable' condition, meaning it can cause the kernel to crash (kernel oops) due to inconsistent internal state management. The root cause is that the mirror array contents were not properly reset after an error, leading to stale or invalid data being referenced. Additionally, the check in nfs_pageio_do_add_request() relied on the pg_count value, which could be unreliable; the fix involves changing this test to verify if the list is empty instead, making the check more robust. This vulnerability affects certain versions of the Linux kernel identified by the commit hash a7d42ddb3099727f58366fa006f850a219cce6c8. Although no known exploits are reported in the wild, the vulnerability could be triggered by malicious or malformed NFS requests, potentially causing denial of service through kernel crashes. The vulnerability does not require user interaction but does require access to the NFS subsystem, which may be exposed in networked environments. The patch involves resetting the mirror array contents properly during error cleanup and improving the robustness of the request addition logic.

For European organizations, the impact of CVE-2021-47167 primarily concerns availability and system stability. Since the vulnerability can cause kernel crashes, systems acting as NFS clients or servers could experience denial of service, disrupting file sharing and critical operations dependent on NFS. This is particularly significant for enterprises and public sector organizations relying on Linux-based infrastructure for storage and network file systems. The disruption could affect data availability, leading to operational downtime and potential loss of productivity. While confidentiality and integrity impacts are not directly indicated, the instability could be leveraged as part of a broader attack chain. Given the widespread use of Linux in European data centers, cloud environments, and embedded systems, the vulnerability poses a moderate risk. However, the lack of known exploits and the requirement for NFS access somewhat limit the attack surface. Organizations with exposed NFS services or those using NFS in multi-tenant environments should be particularly vigilant.

European organizations should prioritize applying the official Linux kernel patches that address CVE-2021-47167 as soon as they are available. Until patched, organizations should restrict access to NFS services by implementing strict network segmentation and firewall rules to limit NFS traffic to trusted hosts only. Monitoring kernel logs for Oops or crash messages related to NFS can help detect exploitation attempts. Additionally, disabling or limiting NFS usage where feasible, especially on systems exposed to untrusted networks, reduces risk. For environments where patching is delayed, consider deploying kernel crash recovery mechanisms and ensuring robust backup and failover strategies to minimize downtime. Security teams should also review NFS configurations to enforce authentication and encryption where supported, reducing the risk of unauthorized access. Finally, maintain up-to-date inventory of Linux kernel versions in use to identify vulnerable systems promptly.