CVE-2019-6533 in PR100088 Modbus Gateway
Summary
by MITRE
Registers used to store Modbus values can be read and written from the web interface without authentication in the PR100088 Modbus gateway versions prior to Release R02 (or Software Version 1.1.13166).
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/09/2020
The vulnerability described in CVE-2019-6533 represents a critical authentication bypass flaw in the PR100088 Modbus gateway device. This issue affects firmware versions prior to Release R02, specifically software versions older than 1.1.13166, where the device fails to properly enforce access controls for its Modbus register interface. The flaw allows unauthorized remote attackers to directly read and write to registers that store Modbus values through the web-based management interface without requiring any authentication credentials. This represents a fundamental breakdown in the device's security architecture, as it violates core principles of access control and privilege management that are essential for industrial control systems.
The technical implementation of this vulnerability stems from inadequate authentication mechanisms within the web interface component of the Modbus gateway. Modbus registers typically contain critical operational data including sensor readings, control signals, and system configuration parameters that are essential for maintaining proper industrial processes. When these registers can be accessed without authentication, an attacker gains the ability to manipulate system state, read sensitive operational data, or potentially disrupt industrial processes. The vulnerability falls under the category of weak authentication or authentication bypass flaws, which are commonly categorized as CWE-287 in the Common Weakness Enumeration. This weakness directly enables unauthorized access to system resources that should be protected by proper authentication mechanisms.
The operational impact of this vulnerability extends far beyond simple data exposure, particularly within industrial environments where Modbus gateways serve as critical communication bridges between operational technology and information technology systems. An attacker could potentially modify control parameters, alter sensor readings, or manipulate device configurations to cause operational disruptions, safety hazards, or financial losses. The implications are especially severe in manufacturing, energy, and critical infrastructure sectors where industrial control systems rely on accurate data flow and proper device management. This vulnerability creates an attack surface that aligns with several tactics described in the MITRE ATT&CK framework for industrial control systems, particularly those related to privilege escalation and defense evasion, as the attacker can operate undetected while modifying system parameters.
Mitigation strategies for this vulnerability must focus on immediate firmware updates to the affected PR100088 devices, ensuring that all systems are upgraded to Release R02 or later versions where the authentication mechanisms have been properly implemented. Network segmentation should be implemented to isolate these devices from critical operational networks, and access controls should be enforced through proper firewall rules and network access control lists. Additionally, organizations should implement monitoring solutions to detect unauthorized access attempts to Modbus interfaces and establish regular security assessments of industrial control systems. The vulnerability demonstrates the importance of maintaining up-to-date firmware in industrial environments and highlights the need for comprehensive security testing of operational technology devices before deployment in critical infrastructure environments.