TEEPwn: Breaking TEE by Experience

February 2023

## Abstract Trusted Execution Environments (TEEs) are notoriously hard to secure due to the interaction between complex hardware and a large trusted code bases (TCBs). The security provided by TEEs has been broken on a wide variety of devices, including mobile phones, smart TVs and even vehicles. Publicly disclosed TEE vulnerabilities were often exploited directly from the less-trusted Rich Execution Environment (REE). Many of these vulnerabilities were specific for TEEs and required novel exploitation techniques. The TEEPwn experience provides an offensive system-level perspective and dives into the darker corners of TEE Security. It is designed with a system-level approach, where you will experience powerful exploitation of TEE vulnerabilities. The TEEPwn experience is hands-on, gamified and driven by an exciting jeopardy-style Capture the Flag (CTF). Your journey starts by achieving a comprehensive understanding of TEEs, where you will learn how hardware and software concur to enforce effective security boundaries. You will then use this understanding for identifying interesting vulnerabilities across the entire TEE attack surface. You will then be challenged along the path to exploit them in multiple scenarios. All vulnerabilities are identified and exploited on our emulated attack platform, implementing a 64- bit TEEs based on ARM TrustZone. You will take on different roles, as an attacker in control of: * the REE, attempting to achieve privileged code execution in the TEE. * the REE, trying to access assess protected by a Trusted Application (TA). * a TA, aiming to escalate privileges to TEE OS. * a TA, accessing the protected assets of other TAs. TEEPwn will guide you into an unexpected range of attack vectors and TEE-specific exploitation techniques, which may be leveraged for novel and creative software exploits, refining your skills to a new level. ## Agenda * TEE Fundamentals - TEE overview - Security model * ARM TrustZone-based TEEs - TEE SW components - TEE attacker model - TEE attack surface * REE -> TEE attacks - Secure Monitor - TEE OS (SMC interface) - Exploitation: - Vulnerable SMC handlers - Broken design - Unchecked Pointers - Restricted writes - Range checks * REE -> TA attacks - Communicating with TAs - Global Platform APIs - Exploitation: - Type confusion - TOCTOU (Double fetch) * TA -> TEE attacks - TEE OS (Syscall interface) - Drivers - Exploitation: - Unchecked pointers from TA - Vulnerable crypto primitives * TA -> TA attacks - State confusion ## Key Learning Objectives * Explore TEE security at the system level * Gain strong understanding of TrustZone-based TEEs * Identify vulnerabilities across the entire TEE attack surface * Experience TEE-specific exploitation techniques ## Intended Audience * Security Analysts and Researchers, interested in new techniques, * Software Security Developers/Architects interested in TEE software attack techniques. ## Student Prerequisites * Experience with C/C++ programming * Experience with the ARM architecture (AArch64) * Understanding of typical software vulnerabilities * Familiarity with reverse engineering and typical exploitation techniques * Familiarity with modern OS security concepts ## System requirements * Any modern computer system with sufficient memory * We advise to install and use the Chrome browser * A stable Internet connection with sufficient bandwidth ## Student Deliverables During the training you will get access to: * a personal cloud based VM * the exercise registry * the exercise instructions * the CTF server To continue practicing after the training is completed: * a personal offline VM * a temporary token to access the exercise registry - for downloading all training exercises in the offline VM * a copy of the exercise instructions
Cristofaro Mune and Niek Timmers

Cristofaro Mune

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Cristofaro has been in the security field for 20+ years. He has 15+ years of experience with evaluating the software and hardware security of secure devices, as well as 10+ years of experience in testing and assessing the security of Trusted Execution Environments (TEEs).

Niek Timmers

Niek has been analyzing and testing the security of software and hardware of secure devices for over a decade. His interest is typically sparked by technologies where the hardware of the device is fundamentally part of the equation.