CVE-2019-19194 in BLE SDK
Summary
by MITRE
The Bluetooth Low Energy Secure Manager Protocol (SMP) implementation on Telink Semiconductor BLE SDK versions before November 2019 for TLSR8x5x through 3.4.0, TLSR823x through 1.3.0, and TLSR826x through 3.3 devices installs a zero long term key (LTK) if an out-of-order link-layer encryption request is received during Secure Connections pairing. An attacker in radio range can have arbitrary read/write access to protected GATT service data, cause a device crash, or possibly control a device's function by establishing an encrypted session with the zero LTK.
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Analysis
by VulDB Data Team • 03/30/2024
The vulnerability described in CVE-2019-19194 represents a critical flaw in the Bluetooth Low Energy Secure Manager Protocol implementation within Telink Semiconductor's BLE SDK across multiple device families. This issue affects versions released prior to November 2019 and impacts TLSR8x5x through 3.4.0, TLSR823x through 1.3.0, and TLSR826x through 3.3 devices, creating a significant security weakness in the pairing process that undermines the fundamental security guarantees of Bluetooth Low Energy communications. The flaw manifests specifically during Secure Connections pairing when the system encounters out-of-order link-layer encryption requests, leading to the installation of a zero long term key that provides no cryptographic protection.
The technical nature of this vulnerability stems from improper handling of encryption request sequences during the Bluetooth pairing process, which is classified as a weakness in the secure key exchange mechanism. When an out-of-order encryption request is received, the system fails to properly validate the request sequence and instead installs a zero LTK, effectively creating a null encryption state. This condition directly violates the Bluetooth specification requirements for secure connections and creates a pathway for unauthorized access to the device's protected data. The zero LTK essentially provides no cryptographic protection, allowing attackers to establish encrypted sessions that offer no security benefits while maintaining full access to the device's functionality.
The operational impact of this vulnerability is severe and multifaceted, as it enables attackers within radio range to gain arbitrary read and write access to protected GATT service data without authentication. This access can be leveraged to extract sensitive information, modify device configurations, or potentially take control of device functions entirely. The vulnerability also creates opportunities for device crash conditions, which could be exploited for denial of service attacks, and in some cases, may allow for complete device compromise. The attack vector requires only proximity to the target device, making it particularly dangerous in environments where physical access is difficult to control, such as industrial IoT deployments, smart home ecosystems, or wearable devices. This vulnerability directly maps to attack patterns described in the MITRE ATT&CK framework under the T1059 and T1068 techniques for remote code execution and privilege escalation through network services.
Mitigation strategies for this vulnerability require immediate firmware updates to patched versions of the Telink Semiconductor BLE SDK released after November 2019, which address the improper handling of out-of-order encryption requests and ensure proper LTK generation during pairing sequences. Organizations should conduct comprehensive inventory assessments to identify all affected devices and prioritize remediation efforts based on risk exposure. Network segmentation and monitoring of Bluetooth traffic can provide additional defensive layers, while implementing proper device authentication mechanisms and regular security audits can help detect and prevent exploitation attempts. The vulnerability demonstrates the critical importance of proper cryptographic implementation and the necessity of thorough testing of security protocols, particularly in IoT environments where devices may operate without regular security updates. This issue aligns with CWE-310, which addresses cryptographic weaknesses, and represents a failure in the secure implementation of cryptographic key management processes.