CVE-2025-21973 is a vulnerability identified in the Linux kernel's Broadcom NetXtreme (bnxt) Ethernet driver, specifically within the bnxt_get_queue_stats_rx and bnxt_get_queue_stats_tx functions. These functions are responsible for collecting per-queue statistics from software rings associated with network interface queues. The vulnerability arises because these functions access certain ring buffers (cp_ring and tx_ring) without verifying whether the network interface is up or down. The rings are only allocated when the interface is up, but the qstats-get operation, which triggers these functions, is allowed even when the interface is down. Consequently, if qstats-get is executed while the interface is down, the driver attempts to access unallocated memory, leading to a NULL pointer dereference and a kernel panic. This results in a denial-of-service (DoS) condition due to the kernel crash. The issue is reproducible by bringing the network interface down and then executing qstats-get commands, as demonstrated by the provided reproducer scripts. The kernel panic manifests as a page fault in kernel mode, with detailed call traces pointing to the bnxt_get_queue_stats_rx function. This vulnerability is rooted in improper null pointer checks and inadequate state validation within the bnxt driver code. While no known exploits are reported in the wild, the flaw can be triggered locally by users with the ability to execute network statistics queries, potentially causing system instability or downtime. The vulnerability affects specific Linux kernel versions identified by commit hashes, and a fix involves adding appropriate null checks to prevent access to unallocated rings when the interface is down.

For European organizations, the impact of CVE-2025-21973 primarily involves potential denial-of-service conditions on Linux systems utilizing Broadcom NetXtreme Ethernet hardware. This can lead to unexpected kernel panics and system crashes, disrupting network connectivity and critical services. Organizations relying on Linux servers for network infrastructure, cloud services, or data centers may experience outages or degraded performance. The vulnerability could affect environments where network interfaces are frequently cycled or managed dynamically, such as in virtualized or containerized deployments. Although exploitation requires local access and the ability to invoke network statistics queries, insider threats or compromised accounts could leverage this flaw to cause service interruptions. The lack of remote exploitability limits the threat surface, but the resulting kernel panic could impact availability of critical systems, leading to operational disruptions and potential financial losses. Additionally, recovery from kernel panics may require manual intervention, increasing administrative overhead. Given the widespread use of Linux in European enterprises, especially in telecommunications, finance, and government sectors, the vulnerability poses a tangible risk to system stability and service continuity.

To mitigate CVE-2025-21973, European organizations should: 1) Apply the official Linux kernel patches that address this vulnerability by adding null pointer checks in the bnxt driver to prevent access to unallocated rings when the interface is down. 2) Identify and inventory all systems running affected Linux kernel versions with Broadcom NetXtreme Ethernet hardware. 3) Implement strict access controls to limit who can execute network statistics queries or perform network interface state changes, reducing the risk of local exploitation. 4) Monitor system logs and kernel messages for signs of kernel panics or crashes related to the bnxt driver, enabling early detection of attempted exploitation or instability. 5) In environments where patching is delayed, consider temporarily disabling or avoiding the use of qstats-get operations on interfaces that may be down, or avoid bringing interfaces down unnecessarily. 6) Incorporate this vulnerability into incident response and system hardening policies, ensuring that administrators are aware of the risk and remediation steps. 7) For critical systems, consider deploying kernel live patching solutions if available to minimize downtime during patch application. These targeted measures go beyond generic advice by focusing on controlling the specific operations that trigger the vulnerability and ensuring rapid patch deployment.