CVE-2021-34149 in CC256XCQFN-EM (BrakTooth)
Summary
by MITRE • 09/07/2021
The Bluetooth Classic implementation on the Texas Instruments CC256XCQFN-EM does not properly handle the reception of continuous LMP_AU_Rand packets, allowing attackers in radio range to trigger a denial of service (deadlock) of the device by flooding it with LMP_AU_Rand packets after the paging procedure.
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Analysis
by VulDB Data Team • 09/10/2021
The vulnerability identified as CVE-2021-34149 affects the Bluetooth Classic implementation within Texas Instruments CC256XCQFN-EM hardware modules, representing a critical denial of service weakness that can be exploited through wireless means. This flaw specifically manifests during the Bluetooth paging procedure when the device receives an excessive number of LMP_AU_Rand packets, which are part of the Bluetooth link management protocol used for authentication and encryption key generation. The issue stems from inadequate input validation and packet handling mechanisms within the embedded Bluetooth stack, creating a scenario where legitimate device operation becomes impossible due to resource exhaustion or state machine corruption.
The technical nature of this vulnerability places it squarely within CWE-400, which categorizes improper handling of input data leading to resource exhaustion or system instability. The attack vector involves an adversary positioned within radio range of the vulnerable device, capable of transmitting continuous LMP_AU_Rand packets that overwhelm the device's processing capabilities. These packets are typically used during the Bluetooth authentication process to generate random numbers for cryptographic operations, but when flooded in excessive quantities, they cause the device to enter a deadlock state where normal Bluetooth operations cease entirely. The underlying flaw demonstrates poor state management and insufficient rate limiting mechanisms in the Bluetooth protocol implementation.
From an operational impact perspective, this vulnerability can severely disrupt services in environments where Bluetooth Classic devices are critical for connectivity, such as industrial IoT deployments, medical devices, or automotive systems. The denial of service condition affects the device's ability to maintain or establish Bluetooth connections, potentially leading to complete service interruption. The attack requires only proximity to the target device and does not necessitate complex authentication or specialized equipment, making it particularly dangerous in environments where physical access is difficult to control. The vulnerability can be exploited by any attacker within the wireless range, potentially causing cascading failures in connected systems that rely on Bluetooth Classic functionality.
Mitigation strategies for this vulnerability should encompass both immediate and long-term approaches to address the root cause. Device manufacturers should implement rate limiting mechanisms to control the frequency of LMP_AU_Rand packet processing, ensuring that the device can handle legitimate authentication traffic without being overwhelmed by malicious flooding. The implementation should include proper state machine validation to prevent deadlock conditions and maintain system stability during abnormal packet sequences. Network administrators should consider implementing Bluetooth monitoring solutions to detect anomalous packet patterns and alert on potential exploitation attempts. Additionally, firmware updates from Texas Instruments should be prioritized to address the specific implementation flaws in the CC256XCQFN-EM hardware, with patch management procedures established to ensure timely deployment across affected deployments. The vulnerability also highlights the importance of applying the principle of least privilege in wireless communications and implementing proper network segmentation to limit the potential impact of such attacks.