CVE-2025-3885 is a medium-severity vulnerability affecting the Harman Becker MGU21 device, specifically its Bluetooth functionality implemented via the BCM89359 wireless chipset. The vulnerability arises from improper input validation (CWE-20) within the Bluetooth stack, where the device fails to adequately validate incoming Bluetooth frames. This flaw allows a network-adjacent attacker to send specially crafted Bluetooth frames that can trigger a denial-of-service (DoS) condition, effectively disrupting the normal operation of the device. Notably, exploitation does not require any authentication or user interaction, which lowers the barrier for attackers. The affected firmware version is MGU21_22-07 with LMP Version 5.0 (0x9) and LMP Subversion 0x420d. The CVSS v3.0 base score is 5.3, reflecting a medium severity level, with the vector indicating that the attack requires adjacent network access (AV:A), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no impact on confidentiality or integrity (C:N/I:N), but high impact on availability (A:H). There are no known exploits in the wild at this time, and no patches have been linked yet. The vulnerability was reserved in April 2025 and published in May 2025. The core technical issue is the lack of proper validation of Bluetooth frames, which can be exploited to crash or otherwise incapacitate the device, leading to service disruption.

For European organizations, the impact of this vulnerability can be significant depending on the deployment of Harman Becker MGU21 devices within their environments. These devices are commonly used in automotive infotainment systems and potentially in other embedded Bluetooth-enabled systems. A successful DoS attack could disrupt critical communication or infotainment functions, leading to operational interruptions, reduced user experience, and potential safety concerns in automotive contexts. Since the attack requires only network-adjacent access via Bluetooth, attackers in proximity to affected devices could exploit this vulnerability without needing physical access or credentials. This could be particularly impactful in environments with many vehicles or devices in close quarters, such as corporate fleets, public transportation, or automotive service centers. While the vulnerability does not compromise confidentiality or integrity, the availability impact could affect business continuity and user trust. Additionally, the lack of patches means organizations must rely on mitigations until official updates are released.

Given the absence of available patches, European organizations should implement specific mitigations to reduce the risk of exploitation. First, limit physical and network access to affected devices by enforcing strict Bluetooth usage policies, including disabling Bluetooth when not in use and restricting pairing to trusted devices only. Employ Bluetooth monitoring tools to detect anomalous or malformed Bluetooth frames indicative of an attack attempt. Where possible, segment networks to isolate devices with the Harman Becker MGU21 chipset from general user environments to reduce exposure. Organizations should also engage with Harman Becker or their automotive suppliers to obtain firmware updates or security advisories and plan for timely patch deployment once available. Additionally, educating staff and users about the risks of unauthorized Bluetooth connections and encouraging vigilance in public or high-density areas can help reduce attack opportunities. Finally, consider deploying intrusion detection systems capable of monitoring Bluetooth traffic for suspicious activity.