CVE-2020-7537 in Modicon M580
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-2020-7537 represents a critical weakness in industrial control systems manufactured by Schneider Electric, specifically affecting their Modicon M580, M340, Quantum, and Premium controller series. This flaw falls under the Common Weakness Enumeration category 754, which addresses improper checks for unusual or exceptional conditions within software applications. The vulnerability manifests when these controllers receive specially crafted Read Physical Memory requests transmitted via the Modbus protocol, creating a potential pathway for malicious actors to disrupt critical industrial operations. The affected devices operate within environments where continuous operation is paramount, making this vulnerability particularly dangerous as it could lead to complete system outages.
The technical mechanism behind this vulnerability involves the controllers' insufficient validation of input parameters within the Modbus communication protocol implementation. When a malformed Read Physical Memory request is transmitted to the affected controllers, the system fails to properly handle the exceptional condition that arises from the unusual request structure. This improper handling causes the controller to enter a state where it cannot process further legitimate requests, effectively creating a denial of service condition. The vulnerability exploits the lack of proper boundary checking and input validation that should occur during Modbus request processing, allowing attackers to send crafted payloads that trigger unexpected behavior in the controller's memory management subsystem. The flaw demonstrates a classic example of inadequate error handling where exceptional conditions are not properly anticipated or managed, leading to system instability and potential operational disruption.
From an operational standpoint, the impact of CVE-2020-7537 extends beyond simple service interruption to potentially compromise the integrity of industrial processes that depend on these controllers. In manufacturing environments, power generation facilities, or water treatment plants, where Modicon controllers manage critical infrastructure, a denial of service attack could result in production halts, safety system failures, or environmental hazards. The vulnerability's exploitation requires minimal technical expertise to craft the malicious Modbus requests, making it particularly dangerous for industrial networks that may lack robust network segmentation or intrusion detection capabilities. Organizations operating these controllers face significant risk as the attack can be executed remotely over network connections, potentially allowing adversaries to disrupt operations without physical access to the equipment. The vulnerability also aligns with tactics described in the MITRE ATT&CK framework under the 'Execution' and 'Impact' domains, where adversaries can leverage weak input validation to achieve system compromise and operational disruption.
Mitigation strategies for this vulnerability must address both immediate protective measures and long-term architectural improvements to industrial control system security. Organizations should implement network segmentation to isolate affected controllers from general corporate networks, deploy Modbus-specific network monitoring tools to detect anomalous traffic patterns, and establish robust access controls for Modbus communications. The most effective immediate solution involves applying firmware updates provided by Schneider Electric that address the improper input validation in the Modbus implementation. System administrators should also configure controllers to limit the number of concurrent Modbus connections and implement rate limiting to prevent abuse of the vulnerability. Additionally, implementing network access control lists and disabling unnecessary Modbus services can significantly reduce the attack surface. Organizations should conduct regular vulnerability assessments targeting their industrial control systems, particularly focusing on protocol-level weaknesses that could lead to denial of service conditions. The remediation process should also include establishing incident response procedures specifically designed for industrial control system disruptions, ensuring that operators can quickly identify and respond to potential exploitation attempts. This vulnerability underscores the importance of applying security patches promptly and maintaining comprehensive inventory management of industrial control system components to ensure all devices receive appropriate security updates.