CVE-2017-7924 in MicroLogix 1100
Summary
by MITRE
An Improper Input Validation issue was discovered in Rockwell Automation MicroLogix 1100 controllers 1763-L16BWA, 1763-L16AWA, 1763-L16BBB, and 1763-L16DWD. A remote, unauthenticated attacker could send a single, specially crafted Programmable Controller Communication Commands (PCCC) packet to the controller that could potentially cause the controller to enter a DoS condition.
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Analysis
by VulDB Data Team • 01/13/2021
The vulnerability identified as CVE-2017-7924 represents a critical improper input validation flaw within Rockwell Automation MicroLogix 1100 controllers, specifically affecting models 1763-L16BWA, 1763-L16AWA, 1763-L16BBB, and 1763-L16DWD. This issue resides in the Programmable Controller Communication Commands (PCCC) protocol implementation, which serves as the primary communication interface for industrial control systems. The flaw stems from inadequate validation of incoming data packets, creating a pathway for malicious actors to exploit the controller's communication stack. The vulnerability is particularly concerning because it allows for remote exploitation without requiring authentication credentials, making it accessible to any attacker with network access to the affected devices. The PCCC protocol operates at the application layer of industrial communication stacks and is commonly used for programming and configuration activities, making it a prime target for adversaries seeking to disrupt industrial operations. This weakness aligns with CWE-20, Improper Input Validation, which is classified as a fundamental software security flaw that frequently leads to various types of attacks including denial of service, code execution, and data manipulation. The vulnerability's impact is amplified by the industrial control environment where these controllers operate, as they typically manage critical infrastructure operations in manufacturing, process control, and automation systems.
The technical exploitation of this vulnerability occurs through the transmission of a single, specially crafted PCCC packet to the affected controller. The malformed packet contains sequences that bypass input validation checks within the controller's firmware, causing the device to process invalid data structures that ultimately lead to a denial of service condition. When the controller receives the malformed packet, its communication stack fails to properly handle the unexpected input, resulting in a system crash or reboot that renders the controller non-operational. The specific nature of the PCCC packet manipulation targets the controller's protocol parser, which lacks sufficient bounds checking and input sanitization mechanisms. This type of attack represents a classic example of a buffer overflow or input parsing vulnerability where the controller's firmware fails to validate packet lengths, content types, or sequence structures before processing. The attack vector is particularly dangerous because it requires no prior authentication, making it accessible to adversaries who may only have network visibility or access to the industrial network segment. From an operational perspective, this vulnerability creates a significant risk to industrial continuity since the affected controllers are often deployed in mission-critical applications where downtime can result in production losses, safety hazards, or environmental impacts. The controller's failure mode is characterized by complete service disruption rather than partial functionality degradation, meaning that the entire control system may become inoperable until manual intervention or power cycling occurs.
The operational impact of CVE-2017-7924 extends beyond simple service disruption to encompass broader industrial control system security concerns. When a MicroLogix 1100 controller enters a denial of service state, it can cause cascading failures throughout the connected automation network, potentially affecting multiple downstream devices and processes that depend on the controller's output for proper operation. The vulnerability's remote nature means that attackers can exploit it from outside the industrial network perimeter, potentially targeting controllers through exposed network services or through compromised network segments. This attack scenario aligns with ATT&CK technique T1499.001, which covers Network Denial of Service, and represents a significant threat to industrial cybersecurity posture. The affected controllers are commonly used in manufacturing environments where they control critical processes such as conveyor systems, packaging equipment, and process control loops. The DoS condition can result in production halts, quality control issues, and potential safety hazards if the controllers manage safety-critical functions. Organizations operating these devices face the challenge of maintaining operational continuity while addressing the vulnerability, as many industrial control systems cannot tolerate extended downtime for patching operations. The vulnerability also highlights the broader issue of legacy industrial systems that were not designed with modern cybersecurity considerations in mind, often lacking the ability to receive timely security updates or patches. Recovery from such an attack typically requires manual intervention, including power cycling the device or physical access to restore normal operations, which can be problematic in remote or hazardous environments.
Mitigation strategies for CVE-2017-7924 should focus on both immediate defensive measures and long-term architectural improvements to industrial control system security. Network segmentation represents a critical first step, isolating affected controllers from general network access through dedicated industrial networks or virtual local area networks that limit exposure to unauthorized access. Implementing network access control lists and firewalls specifically configured to block PCCC protocol traffic from untrusted sources can significantly reduce the attack surface. Organizations should also consider deploying intrusion detection systems that monitor for unusual communication patterns or malformed PCCC packets that could indicate exploitation attempts. The implementation of network monitoring tools capable of identifying and alerting on suspicious traffic patterns can provide early warning of potential attacks. Additionally, regular network audits should be conducted to identify and isolate any unpatched controllers that may be exposed to the internet or untrusted network segments. From a compliance perspective, this vulnerability should be addressed in accordance with industrial security standards such as NIST SP 800-82, which provides guidelines for the security of industrial control systems. The vulnerability also underscores the importance of maintaining up-to-date security assessments and risk evaluations for industrial control environments, as many legacy systems continue to operate without adequate security measures. Organizations should also consider implementing zero-trust network architectures that verify all communications regardless of source location, which can help prevent exploitation of similar input validation vulnerabilities. Regular security training for industrial personnel on recognizing potential security incidents and understanding the operational impact of denial of service attacks is also essential for maintaining robust security postures in industrial environments.