CVE-2025-1221 in Zigbee
Summary
by MITRE • 07/30/2025
A Zigbee Radio Co-Processor (RCP), which is using SiLabs EmberZNet Zigbee stack, was unable to send messages to the host system (CPCd) due to heavy Zigbee traffic, resulting in a Denial of Service (DoS) attack, Only hard reset will bring the device to normal operation
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Analysis
by VulDB Data Team • 07/30/2025
The vulnerability identified as CVE-2025-1221 affects Zigbee Radio Co-Processors that utilize the Silicon Labs EmberZNet Zigbee stack implementation. This issue manifests as a denial of service condition where the RCP fails to communicate with the host system through the CPCd (Common Peripheral Communication daemon) under conditions of high Zigbee network traffic. The affected devices operate within Zigbee network infrastructures where the RCP serves as a critical communication intermediary between the physical radio layer and the application layer running on the host processor. The EmberZNet stack provides the foundational protocol implementation for Zigbee networks, enabling device discovery, routing, and message transmission across mesh networks. When network traffic exceeds certain thresholds, the RCP becomes overwhelmed with processing demands, causing it to drop messages intended for the host system. This failure mode represents a fundamental flaw in the resource management and traffic handling capabilities of the embedded firmware, creating a condition where legitimate network operations cannot proceed normally while the device remains functionally impaired.
The technical root cause stems from inadequate buffer management and queue handling within the RCP firmware implementation. When heavy Zigbee traffic occurs, the device's internal message queues become saturated, preventing the proper processing and forwarding of communication packets to the host system. This condition creates a cascading failure where the CPCd loses connectivity to the RCP, effectively isolating the Zigbee network functionality from the application layer. The vulnerability specifically impacts the communication protocol stack's ability to handle high-throughput scenarios, where multiple concurrent transactions or network events occur simultaneously. The firmware's inability to gracefully handle queue overflow conditions or implement proper traffic shaping mechanisms results in the complete communication breakdown between the RCP and host system. This represents a classic resource exhaustion vulnerability where the system's finite buffer space becomes overwhelmed, leading to a complete operational failure that requires physical intervention through hard reset to restore normal functionality.
The operational impact of this vulnerability extends beyond simple service interruption to encompass complete network partitioning within Zigbee ecosystems. In smart home and industrial IoT deployments, this DoS condition can render entire Zigbee networks non-functional, affecting lighting controls, security systems, environmental monitoring, and other connected devices that rely on the RCP for proper operation. The requirement for hard reset to restore functionality creates significant operational challenges, particularly in remote or hard-to-access deployments where physical access to devices may be limited. Network administrators and system integrators face the challenge of maintaining service availability while dealing with intermittent failures that occur under specific traffic conditions. The vulnerability affects both residential and commercial Zigbee installations, potentially impacting critical infrastructure systems where continuous operation is required. Organizations using Zigbee-based solutions must account for the possibility of complete network outages during periods of high activity, creating operational risk that can affect business continuity and user experience.
Mitigation strategies for this vulnerability should focus on implementing traffic management and monitoring solutions to prevent the conditions that trigger the DoS state. Network administrators should implement traffic shaping policies to limit concurrent message transmission and establish monitoring systems that can detect early warning signs of queue saturation. Firmware updates from Silicon Labs should be prioritized to address the underlying buffer management issues within the EmberZNet stack implementation. Network design considerations should include proper load distribution across multiple RCPs to prevent single points of failure, and redundant communication paths should be established to maintain operational integrity during transient traffic spikes. The implementation of watchdog mechanisms within the host system can help detect communication failures and automatically initiate recovery procedures. Organizations should also consider implementing network segmentation strategies that isolate high-traffic zones from critical control systems to minimize the impact of potential DoS conditions. This vulnerability aligns with CWE-400, which addresses improper resource management, and maps to ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the need for robust resource management and traffic control in embedded networking systems.