The return of software vulnerabilities in the Brazilian voting machine

Abstract

This paper presents a detailed and up-to-date security analysis of the voting software used in Brazilian elections based on results obtained by the authors in a recent hacking challenge organized by the national electoral authority. During the event, multiple serious vulnerabilities were detected in the voting software, which when combined compromised the main security properties of the equipment, namely ballot secrecy and software integrity. The insecure storage of cryptographic keys, hard-coded directly in source code and shared among all machines, allowed full content inspection of the software installation memory cards, after which two shared libraries missing authentication signatures were detected. Injecting code in the libraries allowed the execution of arbitrary code in the machine, violating the integrity of the voting software. Our progress is richly described, to illustrate difficulties and limitations in the testing methodology chosen by the electoral authority, and to inform how teams participating in future challenges can optimize their performance. We trace the history of the vulnerabilities to a previous security analysis, providing some perspective about how the system evolved in the past 6 years. As far as we know, this was the most in-depth compromise of an official large-scale voting system ever performed under such severely restricted conditions.