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edfas.org 13 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 3 THE THREAT OF MALICIOUS CIRCUIT-BOARD ALTERATION: ATTACK TAXONOMY AND EXAMPLES Samuel H. Russ University of South Alabama, Mobile sruss@southalabama.edu EDFAAO (2021) 3:13-22 1537-0755/$19.00 ©ASM International ® INTRODUCTION Circuit boards (or printed wiring boards or PWBs) are nearly ubiquitous in electronic assemblies. Providing both structural support andwiring interconnection, these boards are nowcritically important to nearly all aspects of modern life, fromcell phones to routers to factory automa- tion. Recent work has highlighted how extremely vulner- able circuit boards are to malicious alteration. Starting with an account of an apparent circuit-board “hack,” this article reviews possible ways that attacks can occur and shows examples of what an attack might look like. In one example, a fully functional commercially sold microcon- troller is added to a control bus on a small satellite board. The article concludes with the steps necessary to protect circuit-board design integrity. FIRST INDICATION OF TROUBLE The earliest well-known publication of the malicious alterationof a PWBoccurred in 2018 inBloombergNews. [1] The article detailed how IT professionals at Apple noticed suspicious Internet traffic on their server network. After a bout of troubleshooting, investigators discovered an extra circuit component on recently purchased server moth- erboards. The article asserted that the extra component was roughly the size of a grain of rice. The motherboards came from Supermicro, an extremely reputable vendor in the computer-server industry. The extra circuit compo- nent was allegedly able to access the board’s baseboard management controller, a small supervisory processor found on many server motherboards, and use it to send data over the Internet. The publication launched a firestorm of controversy. One security professional quoted in the article said that finding evidence of a nation-state level attack on hard- ware was like finding “a unicorn jumping over a rainbow.” Government agencies, however, largely discounted the news, andmany regard the alleged incident as discredited. The question that is posed here is much simpler, and hopefully less controversial. How easy is it to “hack” a circuit board? The answer is that it is remarkably easy, and that, rather than being a “unicorn jumping over a rainbow,” it is a very real threat that must be taken seri- ously. Conversely, simple steps can be taken to make the likelihood of an undetected alteration much smaller. A recently published article summarized the threat and suggested remedial steps. [2] As an aside, it is important to understand the assump- tions being made in this article. First, this article is not considering the security of integrated circuits. While clearly an important topic, altering an integrated circuit is complicated, requiring access to the internal structure of an IC and requiring access to very specialized fabrication technology. At any rate, such possible attacks are outside the scope of this article. Second, this article assumes that a “hack” (more accurately, “attack”) is purposeful and malevolent, to gain access to information andpossibly to exert unwanted control. It also assumes that the attacker is a knowledge- able electronics professional. The level of education required to pull off a successful attack will become clear later in this article. Third, this article assumes that the simplest way to hack a circuit board is to add an unwanted component or tomodify a wanted component into an unwanted one. Subtracting a component would likely cause a readily visible malfunction. Another mode of attack would be to somehow embed an unwanted circuit into the circuit board itself, but thiswould be quite expensive and require access to very specialized circuit-board manufacturing capabilities. This type of attack is not out of the question,