CVE-2021-41545 in Desigo DXR2
Summary
by MITRE • 05/10/2022
A vulnerability has been identified in Desigo DXR2 (All versions < V01.21.142.5-22), Desigo PXC3 (All versions < V01.21.142.4-18), Desigo PXC4 (All versions < V02.20.142.10-10884), Desigo PXC5 (All versions < V02.20.142.10-10884). When the controller receives a specific BACnet protocol packet, an exception causes the BACnet communication function to go into a “out of work” state and could result in the controller going into a “factory reset” state.
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Analysis
by VulDB Data Team • 05/12/2022
This vulnerability affects several Desigo controller models including DXR2, PXC3, PXC4, and PXC5 across multiple software versions. The issue stems from improper handling of BACnet protocol packets within the controller's communication stack. When a specifically crafted BACnet packet is received, the system experiences an unhandled exception that triggers a critical failure in the BACnet communication function. This failure condition causes the controller to transition into an "out of work" state, effectively disabling its primary communication capabilities. The vulnerability represents a significant operational risk as it can lead to complete system unavailability and potentially force the controller to enter a factory reset state, resulting in complete loss of configuration and operational data.
The technical flaw manifests as a lack of proper input validation and exception handling within the BACnet protocol processing module. When the controller receives malformed or unexpected BACnet packets, the system fails to gracefully handle the error condition. Instead, the exception propagates through the communication stack causing a cascade failure that ultimately results in the controller's communication functions becoming non-operational. The specific conditions that trigger this vulnerability involve particular packet structures that exploit gaps in the BACnet implementation's error recovery mechanisms. This type of vulnerability aligns with CWE-704 which covers improper handling of exceptions and CWE-248 which addresses exposure of exception information. The vulnerability also demonstrates characteristics of a denial of service condition where normal system operation is disrupted through protocol manipulation.
The operational impact of this vulnerability extends beyond simple communication failure to encompass complete system reliability concerns. Controllers operating in critical infrastructure environments such as building automation systems, industrial control systems, or smart grid applications could face significant operational disruptions. When a controller enters a factory reset state, it not only loses its current configuration but also requires manual intervention to restore proper operation. This can result in extended downtime for facilities that depend on these systems for critical functions such as HVAC control, lighting management, or security systems. The vulnerability creates a potential attack vector where malicious actors could intentionally disrupt building automation systems, leading to operational failures that might affect occupant comfort, energy efficiency, or safety systems. From an attack perspective, this vulnerability maps to ATT&CK technique T1499.004 which covers network disruption and T1566.001 which involves spearphishing with social engineering.
Mitigation strategies should focus on immediate software updates to address the underlying protocol handling issues. Organizations should prioritize deploying the vendor-provided patches that correct the exception handling mechanisms in the BACnet communication functions. Network segmentation and monitoring should be implemented to detect and potentially block suspicious BACnet traffic patterns that could trigger the vulnerability. The implementation of intrusion detection systems specifically designed to monitor BACnet protocol anomalies can provide early warning of potential exploitation attempts. Additionally, maintaining detailed system logs of BACnet communications will aid in forensic analysis if the vulnerability is exploited. Regular security assessments of industrial control systems should include testing for similar protocol handling vulnerabilities, particularly in legacy systems that may not have received recent security updates. The vulnerability also highlights the importance of robust input validation and exception handling in industrial communication protocols, emphasizing the need for comprehensive security testing of control system software before deployment in operational environments.