CVE-2025-21827 is a vulnerability identified in the Linux kernel's Bluetooth USB driver, specifically within the Mediatek btusb component. The issue arises from improper locking when calling the function usb_driver_claim_interface() outside of the probe() context. According to the Linux kernel documentation, this function requires the device lock to be held when invoked from any context other than probe(). The Mediatek btusb driver failed to acquire this lock during certain operations, particularly in the Bluetooth power-on workqueue path (hci_power_on). This improper locking can lead to race conditions and inconsistent states, resulting in errors such as "Failed to claim iso interface" and more severe faults like NULL pointer dereferences where the device driver pointer (intf->dev.driver) is unexpectedly NULL. These errors manifest during USB runtime suspend or power management callbacks, potentially causing kernel crashes or instability. The vulnerability was addressed by adding the necessary locking around usb_driver_claim_interface() calls in the affected Mediatek btusb code, ensuring proper synchronization and preventing these faults. The flaw is rooted in concurrency control within the kernel's USB Bluetooth driver stack and affects Linux kernel versions containing the vulnerable Mediatek btusb implementation prior to the patch. No known exploits have been reported in the wild as of the publication date. The vulnerability does not have an assigned CVSS score but is significant due to its potential to cause kernel crashes and system instability on affected Linux systems using Mediatek Bluetooth USB devices.

For European organizations, this vulnerability could lead to system instability or denial of service on Linux-based systems utilizing Mediatek Bluetooth USB devices. Such devices are common in laptops, embedded systems, and IoT devices. The impact includes potential disruption of Bluetooth connectivity, which can affect peripherals, wireless communication, and device management. In critical environments such as healthcare, manufacturing, or transportation where Linux systems are prevalent, unexpected kernel crashes could interrupt operations or degrade service availability. Although there is no evidence of remote code execution or privilege escalation, the instability caused by NULL pointer dereferences could be exploited indirectly to cause denial of service. Organizations relying on Bluetooth for secure device pairing or data exchange might experience interruptions, impacting productivity or security monitoring. Since the vulnerability relates to kernel-level locking, it affects the integrity and availability of the system rather than confidentiality directly. The absence of known exploits reduces immediate risk, but unpatched systems remain vulnerable to accidental or targeted triggering of the flaw.

European organizations should prioritize updating their Linux kernel to versions that include the patch for CVE-2025-21827. Specifically, ensure that distributions have integrated the fix that adds proper locking around usb_driver_claim_interface() in the Mediatek btusb driver. For environments where immediate patching is not feasible, consider disabling Bluetooth USB devices using Mediatek chipsets temporarily to avoid triggering the vulnerability. System administrators should audit their hardware inventory to identify devices using Mediatek Bluetooth USB components and verify kernel versions. Monitoring kernel logs for the specific error messages "Failed to claim iso interface" or NULL pointer dereferences related to usb_suspend_both or usb_runtime_suspend can help detect attempts to trigger the vulnerability. Additionally, enforcing strict access controls on who can load kernel modules or interact with Bluetooth devices reduces risk. For embedded or IoT devices, coordinate with vendors to obtain firmware or kernel updates incorporating the fix. Finally, incorporate this vulnerability into vulnerability management and patching workflows to ensure timely remediation.