Firmware Counterfeiting and Modification Attacks on Programmable Logic Controllers

Recent attacks on industrial control systems (ICSs), like the highly publicized Stuxnet malware, have perpetuated a race to the bottom where lower level attacks have a tactical advantage. Programmable logic controller (PLC) firmware, which provides a software-driven interface between system inputs and physically manifested outputs, is readily open to modification at the user level. Current efforts to protect against firmware attacks are hindered by a lack of prerequisite research regarding details of attack development and implementation. In order to obtain a more complete understanding of the threats posed by PLC firmware counterfeiting and the feasibility of such attacks, this research explores the vulnerability of common controllers to intentional firmware modifications. After presenting a general analysis process that takes advantage of various techniques and methodologies applied to similar scenarios, this work derives the firmware update validation method used for the Allen-Bradley ControlLogix PLC. A proof of concept demonstrates how to alter a legitimate firmware update and successfully upload it to a ControlLogix L61. Possible mitigation strategies discussed include digitally signed and encrypted firmware as well as preemptive and post-mortem analysis methods to provide protection. Results of this effort facilitate future research in PLC firmware security through direct example of firmware counterfeiting