CVE-2025-21682 is a vulnerability in the Linux kernel's Broadcom NetXtreme (bnxt) Ethernet driver related to the handling of features recalculation after detaching eXpress Data Path (XDP) programs from network interfaces. Specifically, the vulnerability arises because the driver fails to properly re-enable hardware Generic Receive Offload (HW-GRO) after XDP is turned off, leading to inconsistent internal state management. This inconsistency manifests when the driver attempts to reconfigure the Receive Side Scaling (RSS) hash table and ring buffers. The problem is exacerbated by the logic introduced in commit 98ba1d931f61, which optimizes RSS reconfiguration only when the effective number of receive rings changes. Due to HW-GRO doubling the effective number of rings, lowering the rings by half can cause the condition to skip RSS map updates. Consequently, the driver may attempt to access freed memory (freed ring buffers), resulting in a NULL pointer dereference and kernel crash (BUG). The crash occurs in the __bnxt_hwrm_vnic_set_rss function during NIC initialization or reconfiguration, potentially causing denial of service (DoS) on affected systems. This vulnerability has existed since XDP support was introduced but became more impactful after the referenced commit. The issue is triggered by sequences of commands detaching XDP programs and adjusting network interface parameters, which are common in environments using advanced packet processing or network function virtualization. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with the vulnerable bnxt driver, typically found in servers and network appliances using Broadcom NetXtreme Ethernet hardware. The impact includes potential denial of service due to kernel crashes triggered by routine network interface reconfigurations involving XDP. This can disrupt critical network services, affecting availability and operational continuity. Organizations relying on high-performance networking, such as data centers, cloud providers, and telecom operators, may experience service interruptions or degraded performance. Although the vulnerability does not directly expose confidentiality or integrity risks, the resulting instability could be exploited as part of a broader attack chain or cause significant operational disruption. The lack of known exploits reduces immediate risk, but the complexity of the issue and its presence in widely used Linux kernels necessitate prompt attention. European entities with extensive Linux infrastructure, especially those using Broadcom NICs and advanced networking features like XDP, are at higher risk.

To mitigate this vulnerability, European organizations should: 1) Apply the latest Linux kernel patches that address this bnxt driver issue as soon as they become available, ensuring the fix for proper feature recalculation after XDP detachment is included. 2) Temporarily avoid detaching XDP programs or reconfiguring network interfaces in ways that trigger the problematic code path until patched. 3) Monitor kernel logs for signs of NULL pointer dereferences or crashes related to bnxt driver functions. 4) Use kernel live patching solutions if available to minimize downtime during patch deployment. 5) Validate network driver versions and hardware compatibility in their environments, prioritizing updates on systems with Broadcom NetXtreme NICs. 6) Implement robust system monitoring and automated recovery mechanisms to quickly detect and respond to kernel crashes. 7) Coordinate with hardware and Linux distribution vendors for timely updates and advisories. These steps go beyond generic advice by focusing on the specific driver and feature interactions involved in the vulnerability.