CVE-2021-34147 in WICED BT Stack (BrakTooth)
Summary
by MITRE • 09/07/2021
The Bluetooth Classic implementation in the Cypress WICED BT stack through 2.9.0 for CYW20735B1 does not properly handle the reception of a malformed LMP timing accuracy response followed by multiple reconnections to the link slave, allowing attackers to exhaust device BT resources and eventually trigger a crash via multiple attempts of sending a crafted LMP timing accuracy response followed by a sudden reconnection with a random BDAddress.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/10/2021
The vulnerability CVE-2021-34147 affects the Bluetooth Classic implementation within the Cypress WICED BT stack version 2.9.0 and earlier, specifically targeting devices equipped with the CYW20735B1 chip. This issue represents a resource exhaustion flaw that stems from inadequate handling of malformed Link Manager Protocol (LMP) timing accuracy responses during Bluetooth connection management processes. The vulnerability is particularly concerning as it can be exploited to cause system instability and potential denial of service conditions within Bluetooth-enabled devices.
The technical flaw manifests when a malicious attacker sends a crafted malformed LMP timing accuracy response followed by rapid reconnection attempts to the same Bluetooth link slave. The WICED BT stack fails to properly validate or sanitize these malformed responses, leading to improper resource allocation and management within the Bluetooth subsystem. The vulnerability is exacerbated by the stack's inability to handle multiple consecutive reconnection attempts with random BDAddresses, which causes the device to consume increasing amounts of memory and processing resources without proper cleanup mechanisms.
This vulnerability impacts the operational integrity of Bluetooth devices by creating a resource exhaustion condition that can ultimately lead to system crashes and complete loss of Bluetooth functionality. The attack vector is particularly dangerous because it requires only a single malicious device to perform repeated attacks against a target device, making it feasible for attackers to disrupt Bluetooth services in environments where multiple devices are connected or in scenarios where devices automatically reconnect to previously paired devices. The timing of the attack is crucial as it must be coordinated to send the malformed LMP response immediately before the sudden reconnection attempts.
The exploitation of this vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under the technique of resource exhaustion, specifically targeting the Bluetooth subsystem through protocol manipulation. The vulnerability is classified as a CWE-400 vulnerability, representing an unchecked resource allocation issue where the system fails to properly manage and limit resource consumption during Bluetooth connection handling. This type of vulnerability is particularly concerning in IoT environments where Bluetooth devices may operate continuously without user intervention, making them susceptible to prolonged exploitation.
Mitigation strategies should focus on implementing proper input validation and sanitization within the Bluetooth stack to prevent malformed LMP responses from causing resource exhaustion. Device manufacturers should consider implementing rate limiting mechanisms to prevent rapid reconnection attempts from overwhelming the Bluetooth subsystem. Additionally, firmware updates should be prioritized to address the root cause within the WICED BT stack implementation, ensuring proper handling of edge cases in LMP protocol processing. Network administrators should also consider implementing monitoring solutions to detect unusual Bluetooth connection patterns that may indicate exploitation attempts.