CVE-2021-47294 is a vulnerability identified in the Linux kernel's netrom subsystem, specifically related to the management of socket timers and their reference counts. The issue arises from a change introduced by commit 63346650c1a9, which transitioned the netrom code to use the sock timer API instead of the older mod_timer() and del_timer() functions. The new API functions, sk_reset_timer() and sk_stop_timer(), manage socket timers differently. Notably, sk_reset_timer() increments the socket's reference count if called on an inactive timer. However, if the timer expires, the reference count is not decremented accordingly in the handler, leading to an unbalanced reference count. This imbalance prevents the socket from being freed properly, potentially causing a resource leak. Over time, this can lead to exhaustion of kernel resources, such as memory or socket descriptors, which may degrade system performance or cause denial of service (DoS). The vulnerability affects multiple Linux kernel versions identified by specific commit hashes, indicating it is present in certain recent or development versions of the kernel. There are no known exploits in the wild currently, and no CVSS score has been assigned. The vulnerability does not appear to allow direct code execution or privilege escalation but can impact system stability due to resource leakage. The issue is technical and specific to kernel developers and maintainers who manage netrom socket timers and reference counting. It requires patching the kernel code to ensure that the socket reference count is decremented appropriately when timers expire, thus preventing resource leaks and ensuring proper socket lifecycle management.

For European organizations, the primary impact of CVE-2021-47294 lies in potential system instability and denial of service conditions on Linux-based systems that utilize the netrom protocol or related socket timer mechanisms. While netrom is a niche protocol primarily used for amateur radio networking, Linux is widely deployed across servers, embedded devices, and infrastructure components in Europe. Organizations running affected kernel versions may experience gradual resource exhaustion leading to degraded performance or crashes, which can disrupt critical services. This is particularly relevant for telecom providers, research institutions, and industrial control systems that may use specialized Linux kernels or custom builds incorporating netrom support. Although the vulnerability does not directly expose data or allow remote code execution, the resulting denial of service can impact availability, a key pillar of cybersecurity. European entities with strict uptime and reliability requirements, such as financial institutions, healthcare providers, and government agencies, could face operational risks if their Linux systems are affected and unpatched. The absence of known exploits reduces immediate risk, but the vulnerability underscores the importance of maintaining updated kernel versions to prevent latent stability issues.

To mitigate CVE-2021-47294, organizations should: 1) Identify Linux systems running affected kernel versions, especially those with netrom protocol support enabled. 2) Apply the official Linux kernel patches that correct the reference count decrement logic in the netrom socket timer handler. If official patches are not yet available, consider backporting the fix from the relevant commit (63346650c1a9) or disabling netrom support if it is not required. 3) Implement monitoring for unusual resource usage patterns, such as increasing socket reference counts or memory leaks, which may indicate the vulnerability is being triggered. 4) Conduct regular kernel updates as part of a robust patch management program to ensure all known vulnerabilities are addressed promptly. 5) For critical infrastructure, consider deploying kernel live patching solutions to minimize downtime during updates. 6) Engage with Linux distribution vendors to confirm when patched kernel versions will be released and prioritize their deployment. 7) Educate system administrators about the importance of kernel resource management and the implications of socket reference count leaks to improve detection and response capabilities.