CVE-2021-47624 is a vulnerability identified in the Linux kernel, specifically within the net/sunrpc subsystem that handles Remote Procedure Call (RPC) transport state changes via the rpc_sysfs_xprt_state_change function. The issue arises from improper reference count management in an error handling path. When the third argument 'buf' passed to this function does not match the expected strings "offline", "online", or "remove", the function returns an error code (-EINVAL) but neglects to decrement the reference counts of two kernel objects: rpc_xprt and rpc_xprt_switch. These objects are initially incremented by rpc_sysfs_xprt_kobj_get_xprt() and rpc_sysfs_xprt_kobj_get_xprt_switch(), respectively. The failure to decrease the reference counts results in a reference count leak, meaning these kernel objects remain allocated and are not freed as expected. Over time, such leaks can accumulate, potentially leading to resource exhaustion in the kernel, which may degrade system performance or cause instability. The fix involves ensuring that when the input does not match the expected values, the code jumps to the appropriate error handling label 'out_put' to properly decrement the reference counts and prevent leaks. This vulnerability does not appear to have known exploits in the wild and lacks an assigned CVSS score. It affects specific Linux kernel versions identified by the commit hash 5b7eb78486cd9ac58bfbd6d84ea0fe2d9fead03b. The vulnerability is subtle and relates to kernel memory management, which is critical for system stability and security.

For European organizations, the impact of CVE-2021-47624 primarily concerns system stability and reliability rather than direct compromise of confidentiality or integrity. Linux is widely used across European enterprises, government agencies, and critical infrastructure, often as the backbone for servers, networking equipment, and cloud environments. A reference count leak in the kernel can lead to gradual resource depletion, causing kernel memory exhaustion or system crashes. This can result in denial of service conditions, disrupting business operations, critical services, or cloud-hosted applications. Organizations with high availability requirements or those running large-scale Linux deployments may experience increased maintenance overhead or unexpected downtime if the vulnerability is exploited or triggered. Although no direct remote code execution or privilege escalation is indicated, the indirect effects on availability can be significant, especially in environments where uptime is critical. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to degrade system performance or stability, facilitating further exploitation.

To mitigate CVE-2021-47624, European organizations should: 1) Apply the official Linux kernel patches that address the reference count leak as soon as they become available from trusted Linux distribution vendors or upstream kernel sources. 2) Monitor kernel updates and subscribe to security advisories from Linux distributions commonly used in their environments (e.g., Debian, Ubuntu, Red Hat, SUSE). 3) Implement proactive kernel memory and resource monitoring to detect abnormal increases in kernel object allocations or memory usage that could indicate leaks. 4) Conduct thorough testing of kernel updates in staging environments before deployment to production to ensure stability. 5) Limit exposure of RPC services to untrusted networks where possible, reducing the attack surface that could trigger the vulnerable code path. 6) Employ system hardening and kernel security modules (e.g., SELinux, AppArmor) to restrict unauthorized access to kernel interfaces. 7) Maintain comprehensive incident response plans to quickly address potential denial of service or system instability events. These steps go beyond generic advice by emphasizing patch management, monitoring for resource leaks, and reducing RPC exposure.