CVE-2018-7794 in Modicon M580
Summary
by MITRE
A CWE-754: Improper Check for Unusual or Exceptional Conditions vulnerability exists in Modicon M580, Modicon M340, Modicon Quantum, Modicon Premium (see security notification for specific versions) which could cause a Denial of Service when reading data with invalid index using Modbus TCP.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2018-7794 represents a critical weakness in several Modicon programmable logic controller models including the M580, M340, Quantum, and Premium series. This issue falls under the Common Weakness Enumeration category 754, which specifically addresses improper checks for unusual or exceptional conditions within software systems. The flaw manifests when these industrial control devices process Modbus TCP requests containing invalid data indices, creating a scenario where normal operational procedures can be disrupted through carefully crafted malicious inputs.
The technical implementation of this vulnerability stems from inadequate error handling mechanisms within the Modicon controllers' Modbus TCP protocol implementation. When a valid Modbus TCP request is received with an invalid index value, the system fails to properly validate the input parameters before attempting data retrieval operations. This failure creates an exception condition that is not adequately managed, leading to system instability and potential complete service interruption. The vulnerability specifically impacts the controllers' ability to handle malformed data requests without proper defensive programming measures.
From an operational standpoint, this vulnerability poses significant risks to industrial control systems where uninterrupted operation is critical for safety and productivity. The denial of service condition can occur during routine data reading operations, potentially disrupting critical manufacturing processes, monitoring systems, or control functions. The impact extends beyond simple service interruption as the affected controllers may require manual intervention or system restarts to recover from the exception state, leading to extended downtime and potential production losses. Organizations relying on these controllers for mission-critical applications face substantial operational risks when this vulnerability is exploited.
The security implications of CVE-2018-7794 align with ATT&CK framework techniques related to denial of service and system compromise. This vulnerability could serve as an initial access point for more sophisticated attacks, as the system instability created by the denial of service condition may provide opportunities for further exploitation. Network administrators and industrial security teams should consider this vulnerability as part of a broader threat landscape where basic system stability is compromised. The issue demonstrates how seemingly minor input validation gaps can create significant operational risks in industrial environments where system reliability is paramount.
Mitigation strategies for this vulnerability should include implementing proper input validation mechanisms within the Modbus TCP implementations, establishing robust exception handling procedures, and deploying network segmentation to limit exposure. Organizations should also consider applying firmware updates from Schneider Electric as soon as available, implementing network monitoring to detect anomalous Modbus TCP traffic patterns, and establishing incident response procedures specifically addressing denial of service conditions in industrial control systems. The vulnerability highlights the importance of defensive programming practices and proper error handling in embedded systems where system availability directly impacts operational safety and business continuity.