CVE-2023-0027 in Modbus TCP Server AOI
Summary
by MITRE • 03/17/2023
Rockwell Automation Modbus TCP Server AOI prior to 2.04.00 is vulnerable to an unauthorized user sending a malformed message that could cause the controller to respond with a copy of the most recent response to the last valid request. If exploited, an unauthorized user could read the connected device’s Modbus TCP Server AOI information.
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Analysis
by VulDB Data Team • 04/11/2023
The vulnerability identified as CVE-2023-0027 affects Rockwell Automation Modbus TCP Server AOI software versions prior to 2.04.00, representing a critical security flaw that undermines the integrity of industrial control systems. This issue stems from inadequate input validation mechanisms within the Modbus TCP server implementation, specifically when processing malformed network messages. The flaw creates a condition where an unauthorized attacker can craft and send specially crafted requests that exploit a response caching mechanism within the controller. When such malformed messages are received, the system fails to properly validate the incoming data and instead responds with a cached copy of the most recent legitimate response, effectively leaking sensitive operational information to unauthorized parties.
The technical nature of this vulnerability aligns with CWE-20, "Improper Input Validation," and demonstrates how insufficient data sanitization can lead to information disclosure in industrial environments. The flaw operates at the application layer of the network stack, specifically targeting the Modbus TCP protocol implementation used for communication between industrial devices and control systems. Attackers can exploit this weakness by sending malformed Modbus requests that trigger the server to return cached responses containing configuration data, device identifiers, or other sensitive information that should remain protected within the controller's memory space. This behavior represents a classic information leakage vulnerability that can provide attackers with valuable intelligence for subsequent attack phases.
The operational impact of CVE-2023-0027 extends beyond simple information disclosure, as it can enable attackers to gain insights into the operational environment of industrial control systems. The leaked information may include device model numbers, firmware versions, communication parameters, and potentially network configurations that could be leveraged for more sophisticated attacks. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1046, "Network Service Scanning,' and T1566, 'Phishing for Information,' as it provides attackers with the means to gather intelligence about target systems without direct physical access. The vulnerability's exploitation does not require privileged access or complex attack chains, making it particularly dangerous in operational technology environments where such systems may be exposed to external networks or have limited security controls.
Organizations should immediately implement mitigation strategies including updating to Rockwell Automation Modbus TCP Server AOI version 2.04.00 or later, which contains the necessary patches to address the input validation issues. Network segmentation and access control measures should be strengthened to limit exposure of industrial control systems to untrusted networks, particularly implementing firewall rules that restrict Modbus TCP traffic to authorized endpoints only. Additionally, network monitoring solutions should be configured to detect anomalous Modbus traffic patterns that might indicate exploitation attempts. Security teams should also conduct comprehensive vulnerability assessments of their industrial control system environments to identify other potentially affected devices and ensure proper configuration management practices are in place to prevent similar issues from occurring in the future. The vulnerability demonstrates the importance of maintaining current security patches in industrial environments and highlights the need for robust security controls in operational technology systems that may be exposed to external threats.