CVE-2025-41657 is a medium-severity vulnerability affecting the Auma AC1.2 product line, specifically units delivered between January 1, 2024, and May 9, 2025. The root cause is the presence of an undocumented active Bluetooth stack on these devices. This Bluetooth functionality is not disclosed in product documentation or expected behavior, leading to an observable behavioral discrepancy (classified under CWE-207: Observable Behavioral Discrepancy). An unauthenticated attacker in physical proximity (adjacent attacker) can exploit this by fingerprinting the device via Bluetooth signals without requiring any user interaction or authentication. Fingerprinting here means the attacker can identify and distinguish these devices from equivalent products, potentially enabling targeted reconnaissance or follow-up attacks. The CVSS 3.1 score of 4.3 reflects a low complexity attack vector (adjacent network), no privileges or user interaction needed, and limited impact confined to confidentiality (information disclosure through fingerprinting). There is no indication of direct compromise of integrity or availability. No patches or exploits in the wild are currently reported, but the presence of an undocumented Bluetooth stack increases the attack surface and may lead to further vulnerabilities if leveraged by attackers.

For European organizations using Auma AC1.2 devices, particularly in industrial or critical infrastructure environments where these products are deployed, this vulnerability poses a risk primarily related to information disclosure. An attacker could perform reconnaissance to identify specific devices and their deployment locations, which may facilitate targeted attacks or espionage. While the vulnerability does not directly allow device control or disruption, the fingerprinting capability can aid adversaries in mapping networked assets and planning more sophisticated attacks. This is especially relevant for sectors such as energy, manufacturing, and utilities where Auma products are commonly used for automation and control. The lack of authentication and user interaction requirements lowers the barrier for exploitation, increasing risk in environments with physical access by unauthorized personnel or where Bluetooth signals can be intercepted from adjacent areas. However, the medium severity and limited impact suggest that the immediate threat is moderate, but it should not be ignored given the strategic importance of affected systems.

To mitigate this vulnerability, European organizations should first conduct an inventory of all Auma AC1.2 devices deployed within the affected delivery window (01.01.2024 to 09.05.2025). Network segmentation and physical security controls should be enhanced to restrict unauthorized physical proximity to these devices, limiting Bluetooth signal exposure. Disabling Bluetooth functionality on the devices, if configurable, should be prioritized to eliminate the attack vector. If disabling is not possible, organizations should monitor for unusual Bluetooth scanning activity in the vicinity of critical assets. Additionally, organizations should engage with Auma for official guidance and request firmware updates or patches that disable or secure the undocumented Bluetooth stack. Incorporating Bluetooth signal detection tools into security monitoring can help detect potential fingerprinting attempts. Finally, raising awareness among operational technology (OT) and security teams about this vulnerability will ensure timely response and risk management.