Dos Exploitation Of Allen-Bradley'S Legacy Protocol Through Fuzz Testing

EtherNet/IP is a TCP/IP-based industrial protocol commonly used in industrial control systems (ICS). TCP/IP connectivity to the outside world has enabled ICS operators to implement more agile practices, but it also has exposed these cyber-physical systems to cyber attacks. Using a custom Scapy-based fuzzer to test for implementation flaws in the EtherNet/IP software of commercial programmable logic controllers (PLC), we uncover a previously unreported denial-of-service (DoS) vulnerability in the Ethernet/IP implementation of the Rockwell Automation/Allen-Bradley MicroLogix 1100 PLC that, if exploited, can cause the PLC to fault. ICS-CERT recently announces this vulnerability in the security advisory ICSA-17-138-03. This paper describes this vulnerability, the development of an EtherNet/IP fuzzer, and an approach to remotely monitor for faults generated when fuzzing.