CVE-2020-7477 in Ethernet Network module 140NOE771x1
Summary
by MITRE
A CWE-754: Improper Check for Unusual or Exceptional Conditions vulnerability exists in Quantum Ethernet Network module 140NOE771x1 (Versions 7.0 and prior), Quantum processors with integrated Ethernet – 140CPU65xxxxx (all Versions), and Premium processors with integrated Ethernet (all Versions), which could cause a Denial of Service when sending a specially crafted command over Modbus.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2020-7477 represents a critical security flaw classified under CWE-754, which specifically addresses improper checks for unusual or exceptional conditions within software systems. This weakness affects a broad range of industrial automation equipment manufactured by Schneider Electric, including the Quantum Ethernet Network module 140NOE771x1 operating on firmware versions 7.0 and earlier, along with various Quantum processors featuring integrated Ethernet capabilities such as the 140CPU65xxxxx series and Premium processors with integrated Ethernet across all versions. The flaw manifests when these devices receive specially crafted Modbus commands over the network, creating a scenario where normal operational procedures can be disrupted through malicious input manipulation.
The technical implementation of this vulnerability stems from inadequate error handling mechanisms within the Modbus protocol implementation of these industrial controllers. When processing Modbus requests containing malformed or unexpected data structures, the affected devices fail to properly validate input parameters and do not implement robust exception handling routines that would normally detect and gracefully manage unusual conditions. This absence of proper input validation creates a pathway for attackers to craft specific command sequences that trigger unexpected behavior in the device's processing logic, ultimately leading to system instability and potential denial of service conditions.
The operational impact of CVE-2020-7477 extends beyond simple service disruption to potentially compromise entire industrial control systems where these devices operate. In industrial environments, particularly those utilizing Modbus protocols for communication between programmable logic controllers and various field devices, a denial of service attack could result in production line halts, process control failures, and significant financial losses. The vulnerability's exploitation does not require authentication or specialized knowledge beyond understanding the Modbus protocol structure, making it particularly dangerous as it can be leveraged by attackers with minimal privileges to disrupt critical infrastructure operations. This characteristic aligns with ATT&CK technique T1499.001, which covers network denial of service attacks that specifically target industrial control systems.
Mitigation strategies for this vulnerability should prioritize immediate firmware updates from Schneider Electric, as these patches typically address the underlying validation issues in the Modbus implementation. Network segmentation and access control measures can provide additional protection by limiting direct network access to these devices from untrusted networks. Implementing network monitoring solutions that can detect anomalous Modbus traffic patterns may help identify potential exploitation attempts. Organizations should also consider deploying intrusion detection systems specifically configured to monitor for Modbus protocol anomalies that could indicate exploitation of this vulnerability. The remediation process must account for operational continuity requirements in industrial environments, ensuring that firmware updates are carefully planned and tested in controlled settings before deployment to production systems, as these devices often operate in mission-critical environments where downtime is unacceptable.