CVE-2020-7543 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 identified as CVE-2020-7543 represents a critical weakness in several Modicon industrial controller models including the M580, M340, Quantum, and Premium series. This flaw manifests as a CWE-754 improper check for unusual or exceptional conditions, which fundamentally undermines the robustness of these industrial control systems. The vulnerability specifically affects the Modbus communication protocol implementation within these controllers, creating a potential pathway for malicious actors to disrupt critical operations through carefully crafted network requests.
The technical exploitation of this vulnerability occurs through a specially crafted Read Physical Memory request sent over the Modbus protocol to the affected controllers. When such a request is processed, the controller fails to properly validate or handle the unusual conditions presented by the malformed memory read request. This improper handling results in the controller entering an undefined state where it becomes unresponsive or completely ceases to function, effectively causing a denial of service condition. The flaw demonstrates a classic lack of proper input validation and error handling mechanisms within the controller's Modbus implementation, allowing malicious inputs to trigger unexpected behavior patterns.
From an operational impact perspective, this vulnerability poses significant risks to industrial environments where these controllers operate. The denial of service condition can disrupt critical manufacturing processes, automation systems, and control operations that depend on these controllers. In scenarios where these controllers manage safety-critical processes, such as chemical processing, power generation, or water treatment facilities, the potential consequences extend beyond simple operational disruption to include safety hazards and regulatory compliance issues. The vulnerability's impact is particularly concerning given that these controllers are deployed in environments where system uptime and reliability are paramount requirements.
Organizations utilizing affected Modicon controllers should implement immediate mitigations to address this vulnerability. The primary recommended approach involves applying the manufacturer's security patches and firmware updates that specifically address the improper input validation in the Modbus implementation. Network segmentation and access control measures should be strengthened to limit direct communication between external networks and these controllers. Additionally, implementing network monitoring solutions that can detect unusual Modbus traffic patterns and abnormal memory read requests will help identify potential exploitation attempts. Security teams should also consider disabling unnecessary Modbus services when not actively required and establish robust incident response procedures to address potential denial of service events. This vulnerability aligns with ATT&CK technique T1499.001 for network denial of service and represents a critical concern for industrial control system security.