Malware in the SGX Supply Chain: Be Careful When Signing Enclaves!

Malware attacks are a significant part of the new software security threats detected each year. Intel Software Guard Extensions (SGX) are a set of hardware instructions introduced by Intel in their recent lines of processors that are intended to provide a secure execution environment for user-developed applications. To our knowledge, there was no serious attempt yet to overcome the SGX protection by exploiting the weaknesses in the software supply chain infrastructure, namely at the level of the development, build or signing servers. While SGX protection does not specifically take into consideration such threats, we show in the current article that a simple malware attack exploiting a separation between the build and signing processes can have a serious damaging impact, practically nullifying SGX integrity protection measures. We also explore two possible mitigations against the attack, one centralized leveraging SGX itself, and one distributed that relies on a smart contract deployed on a blockchain infrastructure. Our evaluation shows that both methods are feasible in practice and their added costs are acceptable for the offered protection.

1 Introduction

A software supply chain attack can be informally defined as the act of compromising legitimate software packages during their development or distribution phases. The number of such attacks showed a tremendous increase recently. A NIST forum presentation [1] reported seven significant events in 2017 compared to only four during the previous three years. One of the most common attack vectors is injecting malicious malware code [1], [2] into legitimate software packages during or between development and distribution phases, such as upon building or signing. The most prominent example is an infected installation package of the well-known CCleaner [3] application that included a malware deployed in the vendor’s build server [4]. The altered binary file was downloaded by 2.27 million customers, with potentially serious effects ranging from keystrokes recording to stealing secret credentials from users.