CVE-2024-1638 is a medium-severity vulnerability in the Zephyr real-time operating system (RTOS), specifically related to its Bluetooth Low Energy (BLE) Generic Attribute Profile (GATT) implementation. The issue arises from improper input validation concerning the enforcement of read/write permissions on Bluetooth characteristics when using LE Secure Connections (LESC) encryption. Zephyr defines permission flags such as BT_GATT_PERM_READ_LESC and BT_GATT_PERM_WRITE_LESC to require LESC encryption for reading or writing attributes. However, these flags only enforce permission checks correctly when combined with other permission flags like BT_GATT_PERM_READ_ENCRYPT or BT_GATT_PERM_READ_AUTHEN for reads, and BT_GATT_PERM_WRITE_ENCRYPT or BT_GATT_PERM_WRITE_AUTHEN for writes. If these additional flags are omitted, the stack erroneously skips permission verification, allowing unauthorized read or write access to BLE characteristics even if LESC is enabled. This flaw stems from improper input validation (CWE-20) in the permission enforcement logic, effectively bypassing intended security controls. Since Zephyr is widely used in embedded and IoT devices, including those with Bluetooth capabilities, this vulnerability could allow attackers within Bluetooth range to access or modify sensitive device data or behavior without proper authentication or encryption enforcement. No public exploits have been reported yet, and no patches are currently linked, indicating that mitigation relies on awareness and configuration review. The vulnerability affects all versions of Zephyr as indicated, making it broadly relevant to any device using Zephyr’s BLE stack with these permission flags misconfigured or incompletely set.

For European organizations deploying IoT devices, embedded systems, or industrial control systems based on Zephyr RTOS with Bluetooth functionality, this vulnerability poses a risk of unauthorized data access and manipulation. Attackers in physical proximity could exploit the flawed permission checks to read sensitive data or write malicious data to BLE characteristics, potentially leading to data leakage, device malfunction, or unauthorized control. This could impact sectors such as manufacturing, healthcare, smart buildings, and automotive industries where Zephyr-powered devices are integrated. The breach of confidentiality and integrity could undermine operational security, cause safety hazards, or enable lateral movement within networks if compromised devices serve as gateways. Given the increasing adoption of IoT and embedded devices in Europe, the vulnerability could affect supply chains and critical infrastructure relying on secure BLE communications. Although exploitation requires Bluetooth proximity, the widespread use of Bluetooth-enabled devices in enterprise and industrial environments increases the attack surface. The lack of authentication enforcement also raises concerns about insider threats or attackers gaining physical access to facilities. Overall, the vulnerability could degrade trust in device security and lead to compliance issues with European data protection regulations if sensitive data is exposed.

1. Review and audit all Zephyr-based devices with BLE functionality to ensure that Bluetooth GATT characteristic permissions are correctly configured. Specifically, verify that BT_GATT_PERM_READ_LESC and BT_GATT_PERM_WRITE_LESC flags are always combined with the appropriate BT_GATT_PERM_READ_ENCRYPT/BT_GATT_PERM_READ_AUTHEN or BT_GATT_PERM_WRITE_ENCRYPT/BT_GATT_PERM_WRITE_AUTHEN flags to enforce proper permission checks. 2. Implement strict Bluetooth device pairing and bonding policies to limit access to trusted devices only, reducing the risk of unauthorized proximity attacks. 3. Monitor BLE communications for anomalous read/write operations that could indicate exploitation attempts. 4. Engage with Zephyr project maintainers and community to track the release of patches or updates addressing this vulnerability and plan timely deployment. 5. For critical deployments, consider additional layers of security such as application-level encryption or authentication to protect sensitive data beyond BLE stack permissions. 6. Educate developers and integrators on secure configuration of BLE permissions within Zephyr to prevent misconfigurations that lead to this vulnerability. 7. Where possible, restrict physical access to Bluetooth-enabled devices and implement environmental controls to reduce the risk of proximity-based attacks.