CVE-2021-47295 is a high-severity vulnerability in the Linux kernel's network scheduling subsystem, specifically related to the tcindex module. The issue arises from a memory leak in the function tcindex_partial_destroy_work, which is responsible for cleaning up resources associated with tcindex_data structures. The vulnerability was identified by Syzbot, an automated kernel fuzzer, which detected that the perfect hash data structure allocated within tcindex_set_parms() was not properly freed during the destruction process. In detail, when tcindex_set_parms() allocates a new tcindex_data instance, it copies certain fields from the old instance but neglects to copy or free the perfect hash. Since tcindex_partial_destroy_work() is tasked with freeing the old tcindex_data, the perfect hash remains allocated, leading to a memory leak. This flaw can cause resource exhaustion on affected systems, potentially degrading performance or causing denial of service (DoS) conditions. The vulnerability does not affect confidentiality or integrity but impacts availability due to the memory leak. The CVSS v3.1 score is 7.5 (high), with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and scope unchanged (S:U). No known exploits are currently reported in the wild. The vulnerability is categorized under CWE-400 (Uncontrolled Resource Consumption). The affected versions correspond to specific Linux kernel commits, indicating that this is a recent fix. The patch details are not provided in the source, but the issue is resolved in updated kernel versions.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable Linux kernel versions with the tcindex module enabled and used in network traffic control configurations. The memory leak can lead to gradual resource exhaustion, causing system instability or denial of service, which can disrupt critical network services or infrastructure. Organizations relying on Linux-based servers, network appliances, or embedded devices in telecommunications, cloud infrastructure, or industrial control systems could experience degraded performance or outages if the vulnerability is exploited or triggered unintentionally. While the vulnerability does not allow for privilege escalation or data compromise, the availability impact can affect business continuity, especially in sectors requiring high uptime such as finance, healthcare, and public services. The lack of required privileges or user interaction means that exploitation could occur remotely and automatically, increasing the risk profile. However, the absence of known exploits in the wild reduces immediate threat but does not eliminate the need for prompt remediation.

European organizations should prioritize updating their Linux kernel to the latest patched versions that address CVE-2021-47295. Since the vulnerability relates to a memory leak in the tcindex module, organizations should audit their use of traffic control configurations that utilize tcindex to assess exposure. Specific mitigation steps include: 1) Applying official Linux kernel patches or upgrading to a kernel version that includes the fix. 2) Reviewing network traffic control policies and disabling or limiting the use of tcindex where feasible until patched. 3) Implementing monitoring for unusual memory consumption patterns on network nodes running Linux kernels with tcindex enabled to detect potential exploitation or resource exhaustion. 4) Employing resource limits and watchdog timers to automatically restart affected services or systems if memory usage exceeds thresholds. 5) Coordinating with Linux distribution vendors for timely patch deployment and validating kernel versions in use across infrastructure. 6) For embedded or specialized devices, liaise with vendors for firmware updates or mitigations. These steps go beyond generic advice by focusing on the specific module and operational context of the vulnerability.