CVE-2020-7542 in Modicon M340
Summary
by MITRE • 12/11/2020
A CWE-754: Improper Check for Unusual or Exceptional Conditions vulnerability exists in Modicon M580, Modicon M340, Legacy Controllers Modicon Quantum & Modicon Premium (see security notifications for affected versions), that could cause denial of service when a specially crafted Read Physical Memory request over Modbus is sent to the controller.
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Analysis
by VulDB Data Team • 12/16/2020
The vulnerability described in CVE-2020-7542 represents a critical security flaw affecting several Modicon controllers including the M580, M340, Quantum, and Premium series from Schneider Electric. This weakness falls under CWE-754, which specifically addresses improper checks for unusual or exceptional conditions within software systems. The vulnerability manifests when these industrial controllers receive specially crafted Read Physical Memory requests over the Modbus protocol, potentially leading to complete system denial of service. The affected controllers operate within critical infrastructure environments where reliability and continuous operation are paramount, making this vulnerability particularly concerning for industrial control systems.
The technical implementation of this vulnerability stems from inadequate error handling within the Modbus communication stack of these controllers. When a malicious actor sends a crafted Read Physical Memory request, the controller fails to properly validate the incoming data structure or memory access parameters. This improper check for unusual conditions allows the malformed request to bypass normal protocol validation mechanisms, causing the controller to enter an unstable state where it cannot process legitimate requests or maintain normal operations. The flaw essentially creates a condition where exceptional input data causes the system to behave unpredictably rather than gracefully handling the error and continuing operation.
From an operational perspective, the impact of this vulnerability extends beyond simple service disruption to potentially compromising entire industrial processes. The denial of service condition can halt production lines, disrupt critical infrastructure operations, and create safety concerns in environments where these controllers manage essential processes. The vulnerability affects legacy industrial control systems that may be deployed in sectors such as manufacturing, energy, water treatment, and transportation systems where controller availability is crucial. The fact that this vulnerability exists in multiple generations of Modicon controllers suggests a systemic issue within the software architecture that requires comprehensive remediation across affected deployments.
Organizations must implement immediate mitigations including network segmentation to isolate affected controllers from general network access, implementing Modbus protocol filtering to block suspicious memory read requests, and applying firmware updates from Schneider Electric as soon as they become available. The vulnerability also highlights the importance of following industrial security standards such as IEC 62443 and NIST SP 800-82 for industrial control systems security. From an attack perspective, this vulnerability maps to ATT&CK technique T1499.004 for network denial of service attacks and could potentially be leveraged as part of broader industrial espionage or sabotage operations targeting critical infrastructure. The affected controllers should be monitored for unusual network traffic patterns that might indicate exploitation attempts, and incident response procedures should be updated to address potential denial of service scenarios involving industrial control systems.