The vulnerability CVE-2026-25508 affects the Espressif Internet of Things Development Framework (esp-idf), specifically versions 5.1.6, 5.2.6, 5.3.4, 5.4.3, and 5.5.2. It arises from an out-of-bounds read condition in the Bluetooth Low Energy (BLE) Attribute Protocol (ATT) Prepare Write handling within the BLE provisioning transport component (protocomm_ble). During provisioning mode, the device accumulates prepared-write fragments in a fixed-size buffer but incorrectly tracks the cumulative length of these fragments. A remote BLE client can exploit this by sending multiple prepare write requests with overlapping offsets, causing the reported cumulative length to exceed the allocated buffer size. This inflated length is then used during the execute-write phase, leading to an out-of-bounds read and potential memory corruption. This can destabilize the device or cause unexpected behavior, potentially impacting device availability and integrity. The vulnerability does not require prior authentication but does require the device to be in provisioning mode, which typically involves user interaction. Espressif has addressed this issue in versions 5.1.7, 5.2.7, 5.3.5, 5.4.4, and 5.5.3. No known exploits are currently reported in the wild. The CVSS v3.1 base score is 6.3, indicating a medium severity level, with attack vector being adjacent network (BLE), low attack complexity, no privileges required, and user interaction needed.

For European organizations, the impact of this vulnerability primarily concerns IoT devices built on Espressif's esp-idf framework that utilize BLE provisioning. Exploitation could lead to memory corruption, causing device crashes or erratic behavior, which may disrupt critical IoT services or industrial control systems relying on these devices. While confidentiality is not directly compromised, the integrity and availability of devices can be affected, potentially leading to denial of service or operational interruptions. This is particularly significant for sectors with high IoT adoption such as manufacturing, smart cities, healthcare, and utilities. Disruptions in these sectors could have cascading effects on operational efficiency and safety. Since exploitation requires physical proximity to the BLE interface and user interaction to enable provisioning mode, the risk is somewhat mitigated but still relevant in environments where devices are accessible to untrusted individuals. Failure to patch could expose organizations to targeted attacks or accidental disruptions during device provisioning or maintenance.

European organizations should immediately audit their IoT device inventory to identify products using affected esp-idf versions (5.1.6, 5.2.6, 5.3.4, 5.4.3, 5.5.2). They must prioritize updating these devices to patched esp-idf versions (5.1.7, 5.2.7, 5.3.5, 5.4.4, 5.5.3) provided by Espressif. Where firmware updates are not immediately feasible, organizations should restrict physical access to BLE interfaces, especially during provisioning phases, and disable BLE provisioning if not required. Implement network segmentation and monitoring for unusual BLE activity to detect potential exploitation attempts. Device manufacturers and integrators should review provisioning workflows to minimize exposure time and consider additional authentication or authorization mechanisms during provisioning. Regular vulnerability scanning and penetration testing focusing on BLE interfaces can help identify residual risks. Finally, maintain awareness of vendor advisories for any emerging exploits or patches related to this vulnerability.