CVE-2017-7575 in Modicon TM221CE16R
Summary
by MITRE
Schneider Electric Modicon TM221CE16R 1.3.3.3 devices allow remote attackers to discover the application-protection password via a \x00\x01\x00\x00\x00\x05\x01\x5a\x00\x03\x00 request to the Modbus port (502/tcp). Subsequently the application may be arbitrarily downloaded, modified, and uploaded.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2017-7575 affects Schneider Electric Modicon TM221CE16R devices running firmware version 1.3.3.3, representing a critical security flaw that exposes application protection mechanisms through improper Modbus protocol implementation. This weakness allows remote attackers to exploit a specific Modbus request pattern consisting of the sequence Z to gain unauthorized access to the device's application protection password. The vulnerability resides in the device's Modbus port implementation on TCP port 502, which serves as the primary communication interface for industrial control systems and is commonly targeted in industrial cyber attacks.
The technical flaw stems from insufficient authentication and authorization controls within the Modbus protocol handler, specifically allowing unauthenticated access to sensitive application protection mechanisms. When the malformed Modbus request Z is transmitted to port 502, the device responds with the application protection password, effectively bypassing all security controls designed to protect the device's configuration and operational integrity. This weakness directly maps to CWE-287 Improper Authentication, where the device fails to properly verify the identity of requesting entities before granting access to protected resources. The vulnerability represents a fundamental failure in the device's security architecture, as it exposes critical system information without requiring any credentials or authorization.
The operational impact of this vulnerability is severe and multifaceted, as it enables attackers to gain complete control over the device's application environment. Once the application protection password is discovered, adversaries can arbitrarily download the current application configuration, modify it to introduce malicious code or alter operational parameters, and then upload the modified version back to the device. This capability allows for persistent compromise of industrial control systems, enabling attackers to manipulate process variables, disrupt operations, or create backdoor access for future exploitation. The vulnerability affects the CIA triad by compromising confidentiality through password disclosure, integrity through unauthorized application modification, and availability through potential operational disruption.
This vulnerability aligns with several ATT&CK framework techniques including T1071.001 Application Layer Protocol: Web Protocols, T1046 Network Service Scanning, and T1059 Command and Scripting Interpreter. The attack chain typically begins with network reconnaissance to identify Modbus-enabled devices, followed by the specific exploitation of the password disclosure mechanism. Organizations implementing industrial control systems should consider this vulnerability in their risk assessments and security monitoring strategies, particularly in environments where OT and IT systems intersect. The threat landscape for industrial control systems has evolved significantly since this vulnerability was disclosed, with adversaries increasingly targeting such weaknesses to establish persistent access within critical infrastructure environments.
Mitigation strategies should include immediate firmware updates from Schneider Electric to address the vulnerability, network segmentation to isolate Modbus traffic, and implementation of network access controls to restrict access to port 502. Additionally, organizations should deploy network monitoring solutions capable of detecting anomalous Modbus traffic patterns and implement regular security assessments of industrial control systems. The vulnerability demonstrates the critical importance of secure protocol implementation in industrial environments and underscores the need for comprehensive security testing of all network interfaces in critical infrastructure devices.