CVE-2020-6085 in Flex IO 1794-AENT-B
Summary
by MITRE • 10/20/2020
An exploitable denial of service vulnerability exists in the ENIP Request Path Logical Segment functionality of Allen-Bradley Flex IO 1794-AENT/B 4.003. A specially crafted network request can cause a loss of communications with the device resulting in denial-of-service. An attacker can send a malicious packet to trigger this vulnerability by sending an Electronic Key Segment with less than 0x18 bytes following the Key Format field.
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Analysis
by VulDB Data Team • 11/21/2020
The vulnerability described in CVE-2020-6085 represents a critical denial of service weakness within Allen-Bradley Flex IO 1794-AENT/B industrial network modules running firmware version 4.003. This device operates within industrial control systems where network reliability and continuous operation are paramount for maintaining production processes. The vulnerability specifically affects the ENIP Request Path Logical Segment functionality, which is part of the Ethernet IP protocol implementation used extensively in industrial automation environments. The affected device serves as a communication gateway between field devices and higher-level control systems, making its stability crucial for overall plant operations.
The technical flaw manifests when the device processes a malformed Electronic Key Segment within an ENIP request. According to the vulnerability analysis, an attacker can exploit this weakness by crafting a network packet containing an Electronic Key Segment with fewer than 0x18 (24) bytes following the Key Format field. This specific byte count represents a critical boundary condition that the device fails to properly validate during packet parsing. The vulnerability stems from inadequate input validation within the device's network protocol handler, where the system does not properly check the length of incoming data segments before attempting to process them. This type of vulnerability falls under CWE-129, Input Validation, and more specifically aligns with CWE-707 Improper Neutralization of Input During Web Page Generation, though in this industrial context the impact is more severe due to operational technology constraints.
The operational impact of this vulnerability extends beyond simple network disruption, as it can lead to complete loss of communications with the affected device, potentially causing cascading failures throughout industrial control networks. When the device becomes unresponsive due to this denial of service condition, it cannot forward or receive critical process data, leading to production halts, safety system failures, or emergency shutdowns. The vulnerability is particularly dangerous in environments where these modules serve as critical communication bridges between sensors, actuators, and control systems, as the loss of connectivity can result in significant financial losses and safety risks. According to ATT&CK framework, this vulnerability maps to T1499.004, Endpoint Denial of Service, and potentially T1595.001, Network Denial of Service, as it affects networked industrial equipment.
Mitigation strategies for this vulnerability should focus on both immediate network-level protections and long-term firmware updates. Organizations should implement network segmentation and access controls to limit who can send packets to these devices, as well as deploy intrusion detection systems that can identify malformed ENIP traffic patterns. The most effective long-term solution requires updating the affected firmware to a version that properly validates input lengths before processing. Network administrators should also consider implementing rate limiting and monitoring for unusual traffic patterns that might indicate exploitation attempts. Given the industrial nature of these devices, it's crucial to follow proper change management procedures when applying firmware updates to avoid disrupting production processes. The vulnerability demonstrates the importance of applying security patches to industrial control systems, as these devices often operate in environments where patch management is challenging but essential for maintaining operational security and continuity.