CVE-2025-21981 is a vulnerability identified in the Linux kernel related to a memory leak in the accelerated Receive Flow Steering (aRFS) subsystem of the ice network driver. The aRFS feature is designed to optimize network packet processing by steering incoming packets to specific CPU cores, improving performance on multi-core systems. The vulnerability arises from improper management of memory allocation during the reconfiguration of Virtual Station Interfaces (VSIs) when a reset occurs. Specifically, the aRFS structures are allocated twice: once during the initial VSI initialization (probe) and again during reset handling, without releasing the previously allocated memory. This leads to a memory leak, as confirmed by kernel memory leak detection tools (kmemleak), which report unreferenced objects of significant size (e.g., 8192 bytes). The leak occurs in kernel worker threads responsible for handling the reset and reconfiguration processes. Although this vulnerability does not directly cause a crash or allow code execution, the memory leak can degrade system performance over time, potentially leading to resource exhaustion on systems with frequent resets or reconfigurations of network interfaces using the ice driver. The ice driver is commonly used for Intel Ethernet controllers, which are prevalent in many server and enterprise environments. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The issue was resolved by adding checks to prevent double allocation of aRFS memory during VSI reset reconfiguration, ensuring proper release of previously allocated resources.

For European organizations, the impact of CVE-2025-21981 primarily concerns systems running Linux kernels with the affected ice driver versions, especially those utilizing Intel Ethernet hardware in data centers, cloud infrastructure, and enterprise servers. The memory leak can lead to gradual degradation of system stability and performance, increasing the risk of system slowdowns or crashes under heavy network load or frequent interface resets. This can affect critical services such as web hosting, cloud computing platforms, telecommunications infrastructure, and financial services that rely on high network throughput and low latency. While the vulnerability does not directly enable remote code execution or privilege escalation, the indirect effects of resource exhaustion could disrupt business operations, cause downtime, and increase operational costs due to the need for manual intervention or system reboots. Additionally, in environments with strict uptime requirements, such as healthcare or industrial control systems, this vulnerability could pose a risk to service availability. Since no active exploits are known, the immediate threat level is moderate, but organizations should proactively address the issue to prevent potential future exploitation or operational impact.

To mitigate CVE-2025-21981, European organizations should: 1) Apply the latest Linux kernel updates that include the patch fixing the aRFS memory leak in the ice driver. Regularly monitor vendor advisories and kernel mailing lists for updates. 2) Audit and monitor network interface reset events and system logs to detect abnormal frequency of resets or memory leak symptoms, such as increasing memory usage by kernel worker threads. 3) Implement proactive resource monitoring and alerting on critical servers to identify early signs of memory leaks or resource exhaustion. 4) Where possible, limit unnecessary network interface resets or reconfigurations, especially in high-availability environments. 5) For environments using custom or older kernels, consider backporting the patch or disabling aRFS if it is not essential, as a temporary workaround. 6) Engage with hardware vendors to ensure firmware and driver compatibility with patched kernels. 7) Incorporate this vulnerability into incident response and vulnerability management workflows to ensure timely remediation. These steps go beyond generic advice by focusing on specific driver and kernel behavior, operational monitoring, and vendor coordination.