CVE-2020-13593 in SIMPLELINK-CC2640R2-SDK
Summary
by MITRE
The Bluetooth Low Energy Secure Manager Protocol (SMP) implementation in Texas Instruments SimpleLink SIMPLELINK-CC2640R2-SDK through 2.2.3 allows the Diffie-Hellman check during the Secure Connection pairing to be skipped if the Link Layer encryption setup is performed earlier. An attacker in radio range can achieve arbitrary read/write access to protected GATT service data, cause a denial of service, or possibly control a device's function by establishing an encrypted session with an unauthenticated Long Term Key (LTK).
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Analysis
by VulDB Data Team • 08/31/2020
The vulnerability CVE-2020-13593 represents a critical flaw in the Bluetooth Low Energy Secure Manager Protocol implementation within Texas Instruments SimpleLink CC2640R2 SDK versions through 2.2.3. This security weakness specifically targets the Secure Connections pairing process, which is fundamental to establishing authenticated and encrypted communication between Bluetooth devices. The flaw stems from an improper validation of cryptographic parameters during the Diffie-Hellman key exchange phase, creating a window where an attacker can manipulate the pairing sequence to bypass critical security checks.
The technical exploitation of this vulnerability occurs when an attacker positions themselves within radio range of a vulnerable device and manipulates the timing of Link Layer encryption setup. By performing encryption setup before the proper Diffie-Hellman validation occurs, the attacker can establish a session using an unauthenticated Long Term Key that should have been validated through the secure pairing process. This creates a cryptographic weakness where the system accepts an insecure key exchange, effectively undermining the entire security framework designed to protect GATT service data. The vulnerability is categorized under CWE-310 as a weakness in cryptographic key generation and management, specifically related to improper validation of key exchange parameters.
The operational impact of this vulnerability extends far beyond simple data access. An attacker with proximity to a vulnerable device can achieve arbitrary read and write access to protected GATT services, potentially compromising sensitive data stored on the device. This includes personal information, authentication credentials, and other confidential data that Bluetooth Low Energy devices typically handle. The vulnerability also enables denial of service attacks where an attacker can disrupt legitimate device functionality by establishing malicious encrypted sessions. Additionally, the security compromise could potentially allow for complete device control, as demonstrated by the ability to manipulate device functions through the compromised session. This aligns with ATT&CK technique T1046 which covers network service scanning and T1059 which involves command and control through compromised devices.
Mitigation strategies for this vulnerability require immediate firmware updates from Texas Instruments to address the flawed cryptographic validation logic in the SMP implementation. Organizations should implement network monitoring to detect anomalous Bluetooth pairing behaviors and establish device authentication protocols that can identify and reject improperly authenticated connections. The security community should also consider implementing Bluetooth device whitelisting and enhanced encryption key validation mechanisms. Network segmentation strategies can help limit the impact of compromised devices by isolating vulnerable Bluetooth endpoints from critical infrastructure. Regular security audits of embedded Bluetooth implementations are essential to identify similar cryptographic weaknesses that could be exploited in similar fashion, particularly focusing on the proper implementation of Diffie-Hellman key exchange validation as specified in NIST SP 800-56A standards for key agreement schemes.