CVE-2020-6087 in Flex IO 1794-AENT-B
Summary
by MITRE • 10/14/2020
An exploitable denial of service vulnerability exists in the ENIP Request Path Data Segment functionality of Allen-Bradley Flex IO 1794-AENT/B. 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 If the ANSI Extended Symbol Segment Sub-Type is supplied, the device treats the byte following as the Data Size in words. When this value represents a size greater than what remains in the packet data, the device enters a fault state where communication with the device is lost and a physical power cycle is required.
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Analysis
by VulDB Data Team • 11/19/2020
The vulnerability described in CVE-2020-6087 represents a critical denial of service weakness within Allen-Bradley Flex IO 1794-AENT/B industrial network devices that operates at the application layer of the network stack. This device functions as an Ethernet I/O module that communicates using the Ethernet Industrial Protocol (ENIP) which is a key component of the Industrial Internet of Things infrastructure. The vulnerability specifically targets the request path data segment functionality that handles incoming network requests for device configuration and control operations. The flaw manifests when the device processes an ANSI Extended Symbol Segment Sub-Type field within incoming packets, creating a condition where the system's memory management becomes compromised due to improper bounds checking.
The technical mechanism behind this vulnerability involves a classic buffer overflow condition that occurs when processing network packet data structures. When the device encounters an ANSI Extended Symbol Segment Sub-Type field in an incoming packet, it interprets the subsequent byte as representing the Data Size in words rather than validating whether this value corresponds to actual available data within the packet boundaries. This parsing error creates a scenario where an attacker can craft a malicious packet with an inflated data size parameter that exceeds the actual remaining packet data. The device's failure to validate this boundary condition causes it to attempt to access memory locations beyond the legitimate packet data, resulting in an unrecoverable fault state that terminates all network communications with the device.
This vulnerability directly maps to CWE-129, which describes improper validation of the length of input data, and also aligns with ATT&CK technique T1499.001 for network denial of service attacks. The operational impact of this vulnerability extends beyond simple service interruption as it creates a complete communication breakdown that requires physical intervention to resolve. Network administrators face the challenge of maintaining industrial control system availability when a single malicious packet can render an entire I/O module inoperable, potentially causing production line shutdowns or safety system failures in critical infrastructure environments. The requirement for a physical power cycle to restore functionality further compounds the operational disruption, as it may not be immediately possible to access the affected device in remote or hazardous locations.
The mitigation strategies for this vulnerability should focus on implementing network segmentation and access control measures to prevent unauthorized network access to industrial devices. Network administrators should deploy intrusion detection systems that can identify and block malformed packets containing the specific ANSI Extended Symbol Segment Sub-Type patterns. Additionally, implementing network access control lists and restricting direct network access to industrial devices through firewalls and network segmentation can significantly reduce the attack surface. The device firmware should be updated to implement proper bounds checking for all incoming packet data structures, ensuring that data size parameters are validated against available packet data before any memory operations are performed. Organizations should also establish procedures for regularly monitoring network traffic for anomalous patterns that may indicate attempts to exploit this vulnerability, while maintaining detailed documentation of device configurations and network access controls to ensure rapid response capabilities during security incidents.