CVE-2021-47419 is a medium-severity vulnerability in the Linux kernel's network scheduler subsystem, specifically within the taprio queuing discipline (qdisc) implementation. The issue arises from improper handling of timer cancellation in the taprio_destroy() function. The taprio qdisc sets a high-resolution timer before receiving packets, and if this timer is not properly cancelled during the destruction of the qdisc, it can lead to use-after-free or double-free conditions. The vulnerability was identified through syzbot, a kernel fuzzing tool, which detected a debug warning related to freeing an active hrtimer object. The root cause is that the ops->reset() callback is not always called, and thus the timer cancellation must be explicitly handled in ops->destroy to prevent kernel memory corruption. The vulnerability affects Linux kernel versions prior to the fix in the 5.14.0-rc6 development branch and potentially other versions using the affected commit hashes. The CVSS 3.1 score is 5.5 (medium), with the vector indicating local access (AV:L), low complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), no confidentiality or integrity impact (C:N/I:N), but causing high impact on availability (A:H). This means exploitation can cause denial of service (kernel crash or instability) but does not allow data leakage or privilege escalation. No known exploits are reported in the wild yet. The vulnerability is technical and requires local access and some privileges to trigger, limiting its exploitation scope but still posing a risk to systems running affected kernel versions, especially those using taprio qdisc for traffic scheduling.

For European organizations, this vulnerability primarily poses a risk of denial of service on Linux systems running affected kernel versions with taprio qdisc enabled. This could impact servers, network appliances, or embedded devices that rely on Linux for traffic shaping or real-time packet scheduling. The denial of service could disrupt critical network functions, degrade service availability, or cause system crashes requiring reboots. Organizations with infrastructure using Linux kernels in the affected versions, especially in telecommunications, cloud providers, or data centers, may experience operational interruptions. Since the vulnerability requires local access and low privileges, insider threats or compromised accounts could exploit it to cause outages. However, there is no direct risk of data breach or privilege escalation. The impact is thus mainly on availability and operational continuity, which can have cascading effects on business processes and service delivery in sectors like finance, healthcare, and public services across Europe.

1. Apply the official Linux kernel patches that address this vulnerability as soon as they are available and tested in your environment. Monitor kernel updates from trusted sources and vendors. 2. If immediate patching is not feasible, consider disabling or avoiding the use of the taprio qdisc in network configurations to eliminate the vulnerable code path. 3. Restrict local access to systems running affected kernels by enforcing strict access controls, limiting user privileges, and monitoring for suspicious activity. 4. Implement kernel hardening and exploit mitigation techniques such as Kernel Address Space Layout Randomization (KASLR) and Control Flow Integrity (CFI) where supported. 5. Regularly audit and monitor system logs for kernel warnings or crashes related to hrtimer or qdisc operations to detect potential exploitation attempts early. 6. For critical infrastructure, consider deploying intrusion detection systems capable of monitoring kernel-level anomalies. 7. Educate system administrators about this vulnerability and ensure they follow secure configuration and patch management best practices.