CVE-2021-34146 in CYW920735Q60EVB (BrakTooth)
Summary
by MITRE • 09/07/2021
The Bluetooth Classic implementation in the Cypress CYW920735Q60EVB does not properly handle the reception of continuous unsolicited LMP responses, allowing attackers in radio range to trigger a denial of service and restart (crash) 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-2021-34146 affects the Bluetooth Classic implementation within Cypress CYW920735Q60EVB evaluation boards, representing a critical flaw in wireless communication protocols that can lead to system-wide disruption. This issue stems from inadequate handling of unsolicited Link Manager Protocol responses, specifically targeting the LMP_AU_Rand packet type that is typically used during authentication procedures. The vulnerability exists within the device's radio frequency processing capabilities where it fails to properly validate incoming LMP packets during the paging phase of Bluetooth connections, creating a condition where malicious actors can exploit this weakness to cause system instability.
The technical flaw manifests when an attacker within radio range transmits continuous LMP_AU_Rand packets to a vulnerable device after the initial paging procedure has been completed. This specific packet type is normally part of the Bluetooth authentication handshake process, but when sent in excessive quantities without proper context or sequence validation, it overwhelms the device's processing capabilities. The implementation lacks proper input sanitization and packet filtering mechanisms that would normally prevent such flooding attacks from disrupting the device's normal operations. This weakness falls under CWE-129, Input Validation, and more specifically CWE-400, Uncontrolled Resource Consumption, as the device cannot properly handle the excessive packet volume that exceeds its processing capacity.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause complete device restarts or crashes that may result in extended downtime for connected systems. This denial of service condition can be particularly problematic for IoT devices, medical equipment, automotive systems, or industrial control systems that rely on continuous Bluetooth connectivity. The attack requires only proximity to the target device, making it accessible to anyone within radio range without requiring sophisticated equipment or advanced technical skills. The vulnerability essentially allows an attacker to remotely force a device into a reboot cycle, potentially causing data loss, service interruption, or even safety hazards in critical systems where continuous operation is essential.
Mitigation strategies for this vulnerability should focus on implementing proper packet filtering and rate limiting mechanisms within the Bluetooth stack to prevent excessive LMP packet processing. Device manufacturers should consider implementing hardware-level protections that can detect and drop anomalous packet sequences before they reach the main processing units. Network administrators should monitor for unusual Bluetooth traffic patterns and implement network segmentation to isolate vulnerable devices from critical systems. The remediation approach aligns with ATT&CK technique T1499.001, Network Denial of Service, and T1566.002, Phishing via Social Engineering, as the attack vector relies on physical proximity and the exploitation of protocol implementation weaknesses. Organizations should prioritize updating firmware to patched versions when available, implementing network monitoring solutions that can detect anomalous Bluetooth traffic patterns, and considering alternative wireless communication protocols for critical applications where such vulnerabilities might pose significant risks.