CVE-2021-22659 in MicroLogix 1400
Summary
by MITRE • 03/25/2021
Rockwell Automation MicroLogix 1400 Version 21.6 and below may allow a remote unauthenticated attacker to send a specially crafted Modbus packet allowing the attacker to retrieve or modify random values in the register. If successfully exploited, this may lead to a buffer overflow resulting in a denial-of-service condition. The FAULT LED will flash RED and communications may be lost. Recovery from denial-of-service condition requires the fault to be cleared by the user.
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Analysis
by VulDB Data Team • 06/03/2026
The vulnerability identified as CVE-2021-22659 affects Rockwell Automation MicroLogix 1400 controllers running firmware versions 21.6 and earlier, representing a critical security flaw in industrial control systems that exposes operational technology infrastructure to remote exploitation. This vulnerability specifically targets the Modbus protocol implementation within these devices, creating a pathway for unauthenticated remote attackers to manipulate system registers through specially crafted network packets. The affected hardware operates in critical industrial environments where reliability and security are paramount, making this vulnerability particularly concerning for manufacturing and process control applications.
The technical flaw manifests as a lack of proper input validation within the Modbus packet processing routine of the MicroLogix 1400 controller firmware. When receiving Modbus requests, the system fails to adequately verify the boundaries and structure of incoming packets, allowing attackers to craft malformed requests that can traverse normal protocol boundaries. This weakness enables attackers to read or modify arbitrary register values within the device's memory space, effectively bypassing normal access controls and authorization mechanisms. The vulnerability stems from improper handling of register addressing parameters within the Modbus implementation, creating a condition where attacker-controlled data can influence memory access patterns and potentially overwrite critical system structures.
The operational impact of this vulnerability extends beyond simple data manipulation to include severe system stability concerns. Successful exploitation can trigger buffer overflow conditions within the controller's memory management system, leading to unpredictable behavior and ultimately resulting in denial-of-service scenarios. When compromised, the affected devices exhibit clear visual indicators through the flashing red FAULT LED, signaling to operators that the system has encountered a critical error condition. Network communications may cease entirely, disrupting production processes and potentially causing significant operational downtime. The recovery process requires manual intervention from system administrators to clear the fault condition, adding to operational complexity and potential production losses.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of inadequate input validation in network services. The attack vector follows ATT&CK technique T1210, specifically targeting remote exploitation through protocol manipulation. Organizations utilizing Rockwell Automation MicroLogix 1400 controllers should implement immediate mitigations including network segmentation to isolate these devices from untrusted networks, deployment of network monitoring solutions to detect anomalous Modbus traffic patterns, and implementation of access control lists to restrict Modbus port access. Firmware updates from Rockwell Automation should be prioritized as the primary remediation strategy, though organizations may need to develop temporary workarounds such as disabling unused Modbus functionality or implementing network-based intrusion detection systems to monitor for exploitation attempts. The vulnerability demonstrates the critical need for robust security practices in industrial environments where traditional cybersecurity controls may be insufficient to protect against sophisticated remote attacks targeting operational technology infrastructure.