CVE-2025-21662 is a vulnerability identified in the Linux kernel specifically within the Mellanox mlx5_core driver, which handles network interface cards (NICs) based on Mellanox hardware. The issue arises in the command handling logic of the mlx5 driver, particularly in the cmd_alloc_index() and cmd_work_handler() functions. When cmd_alloc_index() fails to allocate a command entry, cmd_work_handler() does not properly complete the associated synchronization variable ent->slotted before returning early. This improper handling causes the issuing task to hang indefinitely, as it waits for a completion event that never occurs. The kernel log snippet indicates that a worker thread (kworker) becomes blocked for more than 120 seconds, effectively causing a denial of service (DoS) condition on the affected system. The problem is rooted in the mlx5_core_modify_cq and mlx5_core_modify_cq_moderation functions, which are involved in modifying completion queues and their moderation parameters, critical for network packet processing. This bug can lead to kernel-level task hangs, impacting system responsiveness and network functionality. Although no known exploits are reported in the wild, the vulnerability can cause significant operational disruption, especially in environments relying on Mellanox NICs and the affected Linux kernel versions. The affected versions are identified by specific git commit hashes, indicating this is a low-level kernel code issue fixed in recent patches. The vulnerability does not require user interaction or authentication to trigger, as it occurs within kernel driver operations handling network commands.

For European organizations, the impact of CVE-2025-21662 can be substantial, particularly for data centers, cloud providers, and enterprises using Linux servers equipped with Mellanox network adapters. The vulnerability can cause kernel worker threads to hang, leading to degraded network performance or complete network outages on affected hosts. This can disrupt critical services such as web hosting, cloud infrastructure, financial transaction processing, and telecommunications. Organizations relying on high-performance computing or storage networks using Mellanox hardware are especially at risk. The denial of service condition could also cascade in clustered or virtualized environments, affecting multiple services or tenants. Given the widespread use of Linux in European IT infrastructure, the vulnerability poses a risk to availability and operational continuity. While confidentiality and integrity are not directly impacted, the availability degradation can lead to financial losses, reputational damage, and regulatory compliance issues under frameworks like GDPR if service disruptions affect customer data access or processing.

To mitigate this vulnerability, European organizations should: 1) Identify and inventory Linux systems using Mellanox mlx5 network drivers, focusing on kernel versions corresponding to the affected commit hashes. 2) Apply the latest Linux kernel patches that address CVE-2025-21662 as soon as they become available from trusted sources or vendor distributions. 3) For environments where immediate patching is not feasible, consider temporarily disabling or replacing affected Mellanox NICs with alternative hardware to prevent triggering the bug. 4) Monitor kernel logs for symptoms such as hung kworker threads or repeated cmd_work_handler failures indicating the issue. 5) Implement robust system monitoring and alerting to detect early signs of task hangs or network performance degradation. 6) Engage with hardware and Linux distribution vendors for guidance and support on patch deployment and validation. 7) Test patches in staging environments to ensure stability before production rollout, given the kernel-level nature of the fix. 8) Review and update incident response plans to include procedures for handling kernel-level hangs and network outages related to this vulnerability.