CVE-2021-3433 in zephyrproject-rtos
Summary
by MITRE • 06/29/2022
Invalid channel map in CONNECT_IND results to Deadlock. Zephyr versions >= v2.5.0 Improper Check or Handling of Exceptional Conditions (CWE-703). For more information, see https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-3c2f-w4v6-qxrp
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Analysis
by VulDB Data Team • 07/16/2022
The vulnerability identified as CVE-2021-3433 represents a critical deadlock condition within the Zephyr real-time operating system affecting versions 2.5.0 and later. This issue manifests specifically during Bluetooth Low Energy connection establishment when processing CONNECT_IND packets, creating a scenario where the system becomes unresponsive due to improper handling of exceptional conditions. The flaw resides in the Bluetooth stack implementation where an invalid channel map in the CONNECT_IND message triggers an unexpected state that leads to system deadlock rather than graceful error recovery or connection termination.
The technical root cause of this vulnerability stems from CWE-703, which classifies improper check or handling of exceptional conditions within software systems. In the Zephyr Bluetooth implementation, when a CONNECT_IND packet contains an invalid channel map, the system fails to properly validate this condition before proceeding with connection establishment logic. This validation failure creates a path where the system enters a deadlock state, preventing any further Bluetooth operations from completing successfully. The channel map validation occurs during the connection setup phase where the system attempts to establish communication parameters, but the absence of proper error handling mechanisms causes the thread executing the connection logic to become permanently blocked.
The operational impact of this vulnerability extends beyond simple system unresponsiveness to potentially compromise entire embedded IoT devices running Zephyr-based systems. When a device encounters an invalid channel map during Bluetooth connection establishment, it becomes completely unresponsive to new connection attempts or other Bluetooth operations, effectively rendering the device's wireless communication capabilities non-functional until manual intervention or device reset occurs. This scenario is particularly concerning in IoT deployments where devices may be remotely managed or where continuous connectivity is critical for system operation. The vulnerability affects devices that rely on Zephyr's Bluetooth stack for wireless communication, potentially impacting smart home devices, industrial sensors, medical devices, and other embedded systems where Bluetooth connectivity is essential.
Mitigation strategies for this vulnerability require immediate action from system administrators and developers. The primary recommendation involves upgrading to patched versions of the Zephyr RTOS where the improper exception handling has been corrected through proper validation of channel map parameters in CONNECT_IND packets. Organizations should conduct comprehensive vulnerability assessments to identify all systems running affected Zephyr versions and implement coordinated upgrade schedules. Additionally, implementing monitoring solutions to detect deadlock conditions can provide early warning of potential exploitation attempts. From a security perspective, this vulnerability aligns with ATT&CK technique T1499.004 which involves network denial of service through system resource exhaustion or lockout conditions, though in this case the resource exhaustion manifests as thread deadlock rather than traditional resource depletion. The fix implemented in patched versions typically involves strengthening input validation routines and implementing proper error recovery mechanisms that prevent the system from entering deadlock states when encountering malformed Bluetooth connection parameters.