CVE-2025-37812 is a vulnerability identified in the Linux kernel specifically affecting the cdns3 USB driver, which handles USB3 controller operations. The issue is a deadlock condition occurring when using the Network Control Model (NCM) gadget functionality under the PREEMPT_RT real-time kernel configuration. The deadlock arises because the threaded interrupt handler can be preempted by a softirq (software interrupt), yet both the threaded interrupt handler and the softirq are protected by the same spinlock. This locking design flaw leads to a scenario where the system can become indefinitely blocked, particularly under heavy network traffic conditions such as bidirectional iperf tests over the NCM ethernet link. The vulnerability mirrors a previously fixed deadlock in the cdnsp driver, indicating a similar root cause. The fix involves disabling softirq processing during the execution of the threaded interrupt handler to prevent the deadlock. This vulnerability affects Linux kernel versions identified by the commit hash 7733f6c32e36ff9d7adadf40001039bf219b1cbe and likely other versions incorporating the vulnerable cdns3 driver code. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The vulnerability primarily impacts systems using the PREEMPT_RT patch for real-time capabilities and employing the cdns3 USB controller with NCM gadget functionality, which is common in embedded and specialized networking devices running Linux.

For European organizations, the impact of CVE-2025-37812 can be significant in environments relying on Linux-based embedded systems or network appliances that utilize the cdns3 USB controller with NCM gadget support, especially under real-time kernel configurations (PREEMPT_RT). Such systems are often found in telecommunications infrastructure, industrial control systems, and specialized networking equipment. The deadlock can cause system hangs or unresponsiveness, leading to denial of service (DoS) conditions that disrupt network communications or device operations. This can affect critical services, including industrial automation, telecom services, and real-time data processing, potentially causing operational downtime and impacting service availability. While the vulnerability does not directly lead to privilege escalation or data leakage, the availability impact can be severe in time-sensitive or mission-critical applications. European organizations with deployments in sectors such as manufacturing, telecommunications, and critical infrastructure that leverage Linux real-time kernels and USB networking gadgets are at higher risk. The lack of known exploits reduces immediate threat but does not eliminate the risk of future exploitation, especially as the vulnerability is relatively recent and publicly disclosed.

To mitigate CVE-2025-37812, European organizations should: 1) Apply the official Linux kernel patches that disable softirq processing during the threaded interrupt handler in the cdns3 driver as soon as they become available. Monitoring Linux kernel mailing lists and vendor advisories for patch releases is critical. 2) For systems using PREEMPT_RT kernels, consider temporarily disabling the PREEMPT_RT patch or reverting to a standard kernel if real-time capabilities are not essential, to avoid triggering the deadlock. 3) Limit or control heavy bidirectional network traffic over NCM ethernet links on affected devices until patches are applied, reducing the likelihood of triggering the deadlock. 4) Conduct thorough testing of updated kernels in staging environments to ensure stability and compatibility before deployment. 5) For embedded device vendors and integrators, update firmware and device software to incorporate the fixed kernel versions and distribute updates to customers promptly. 6) Implement monitoring for system hangs or unresponsiveness related to USB networking interfaces to detect potential deadlock occurrences early. 7) Engage with hardware vendors to confirm whether their devices use the affected cdns3 driver and coordinate patching efforts accordingly.