CVE-2021-3430 in zephyrproject-rtos
Summary
by MITRE • 06/29/2022
Assertion reachable with repeated LL_CONNECTION_PARAM_REQ. Zephyr versions >= v1.14 contain Reachable Assertion (CWE-617). For more information, see https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-46h3-hjcq-2jjr
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Analysis
by VulDB Data Team • 07/16/2022
The vulnerability identified as CVE-2021-3430 represents a critical assertion reachability issue within the Zephyr real-time operating system that affects versions 1.14 and later. This flaw manifests through repeated LL_CONNECTION_PARAM_REQ commands, creating a scenario where an attacker can trigger a reachable assertion that leads to system instability. The vulnerability resides in the Bluetooth low energy stack implementation and specifically targets the connection parameter request handling mechanism. According to the CWE-617 classification, this represents a reachable assertion that can be exploited to cause denial of service conditions, making it particularly dangerous in embedded systems where reliability is paramount.
The technical exploitation of this vulnerability occurs when an attacker repeatedly sends LL_CONNECTION_PARAM_REQ packets to a Zephyr-based device. These packets are part of the Bluetooth low energy protocol specification used to request changes to connection parameters such as interval, latency, and timeout values. The flaw arises from insufficient input validation and state management within the connection parameter request processing code. When multiple such requests are received in rapid succession, the system's assertion mechanism is triggered, causing the device to terminate or enter an undefined state. This behavior aligns with the ATT&CK technique T1499.004 for Network Denial of Service, where adversaries exploit protocol implementation flaws to disrupt system availability.
The operational impact of CVE-2021-3430 extends beyond simple denial of service scenarios, particularly in environments where Zephyr-based devices serve critical functions. Devices running affected versions may experience unexpected restarts, application crashes, or complete system lockups when subjected to this attack vector. The vulnerability affects a wide range of IoT devices, wearables, and embedded systems that utilize Zephyr as their underlying operating system for Bluetooth connectivity. Security researchers have noted that the attack requires minimal resources to execute, making it particularly dangerous as it can be triggered remotely without requiring physical access or complex prerequisites. The issue demonstrates poor defensive programming practices where assertions are not properly guarded against malicious input sequences.
Mitigation strategies for CVE-2021-3430 primarily focus on upgrading to patched versions of the Zephyr operating system where the assertion handling has been corrected. The official security advisory recommends updating to Zephyr version 2.5.0 or later, which includes proper input validation and state management improvements. Organizations should also implement network monitoring to detect unusual patterns of LL_CONNECTION_PARAM_REQ traffic that may indicate attempted exploitation. Additional defensive measures include configuring rate limiting for Bluetooth connection parameter requests, implementing proper access controls for Bluetooth interfaces, and conducting regular security assessments of embedded systems. The vulnerability highlights the importance of proper assertion handling in embedded systems and the need for comprehensive testing of protocol implementations against malicious input sequences. From a compliance perspective, this vulnerability may impact organizations subject to standards such as ISO 27001 or NIST cybersecurity frameworks, particularly in areas concerning system availability and robustness.