An Analytical Approach to Modern Binary Deobfuscation

For Reverse Engineers and Malware Analysts

August 2022

## Abstract Code obfuscation has become one of the most prevalent mechanisms aiming to complicate the process of software reverse engineering. It plays a major role on a wide range of domains: from malware threats to protection of intellectual property and digital rights management. "An Analytical approach to Modern Binary Deobfuscation" is a curated training that provides an intensive jump-start into the field of code (de)obfuscation. Over the course of this training, students will receive a comprehensive introduction to the most relevant software obfuscation mechanisms as well as existing deobfuscation techniques to analyze, confront and defeat obfuscated code. ## Key learning objectives - Obtain a high-level overview of the context and scenarios where code obfuscation is used - Gain an in-depth understanding of code obfuscation mechanisms - Build obfuscated code, both from scratch and through available tooling - Develop an understanding of the main code deobfuscation techniques - Learn tooling for analyzing obfuscated code and apply deobfuscation techniques - Become familiar with state of the art (de)obfuscation research literature ## Contents ## Day 1 #### INTRODUCTION, CONTEXT AND MOTIVATION #### DATA-FLOW BASED OBFUSCATIOn - Constant unfolding - Dead code insertion - Encodings - Pattern-based obfuscation #### CONTROL-FLOW BASED OBFUSCATION - Function inlining/outlining - Opaque predicates - Control-flow flattening #### MIXING DATA-FLOW AND CONTROL-FLOW OBFUSCATION - VM-based obfuscation - Hardening VM-based obfuscation EXERCISES
PROJECT: Manually craft a custom obfuscation VM ## Day 2 #### SMT-BASED ANALYSIS - A primer on SMT solvers - Translate code conditions into SMT solver constraints - Program analysis with SMT solvers #### MIXED BOOLEAN-ARITHMETIC - Preliminary concepts - MBA rewriting - Insertion of identities - Opaque constants EXERCISES
PROJECT: Applied MBA to obfuscate the semantics of VM-handlers ## Day 3 #### SYMBOLIC EXECUTION - Reasoning about code in a symbolic way - Working with native code - Working with intermediate representations - Data-flow analysis and compiler optimizations - Extract symbolic formulas - Extract path constraints - Plugging an SMT solver - Attacking obfuscation schemes GUIDED PROJECT: Build your own (toy) symbolic execution engine
PROJECT: Attack obfuscated VM and explore symbolic execution limits ## Day 4 #### PROGRAM SYNTHESIS - Code syntax VS Code semantics - Specifying program behavior - Oracle-based program synthesis - Describing semantics through I/O behavior - Generating I/O pairs - Different synthesis flavors - Practical considerations - Attacking obfuscation schemes #### CONCLUSIONS AND RESEARCH DIRECTIONS GUIDED PROJECT: Build your own code semantics synthesizer
PROJECT: Recover the semantics of MBA-obfuscated VM-handlers ## Tools used * Disassemblers - IDA Free/Home/Pro - Ghidra - radare2 * Obfuscation - Manual obfuscation - O-LLVM - Tigress * Symbolic execution - Miasm - Triton * Program synthesis - Syntia - Msynth - Custom tooling * Other tools - Z3 - Custom tooling ## Teaching methodology Live classes are designed to be dynamic and engaging, making the students get the most out of the training materials and instructor expertise. A clear presentation of the concepts, accompanied by illustrative examples and demos. For each section, there will be practice time allocated. The students will be provided with several exercises to work on, with the continuous support of the instructor. ## Who should attend Reverse engineers, malware analysts and folks within the anti-cheating and software protection industry. It can also be really beneficial for bug hunters, vulnerability researchers, exploit developers and enthusiast security researchers in general. ## Prerequisites - Understanding of basic programming concepts - Familiarity with x86 assembly, C and Python - Knowledge of reverse engineering fundamentals ## System requirements - A working desktop/laptop capable of running virtual machines - 40 GB free hard disk space ## Students will be provided with - A Virtual Machine with all tools, examples and exercises - Access to a private chat with instructor and other students
Arnau Gàmez

Arnau Gàmez i Montolio

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Catalan hacker, reverse engineer and mathematician, with an extensive background in code (de)obfuscation research and Mixed Boolean-Arithmetic expressions, as well as industry experience as a senior malware reverse engineer. Founder of Fura Labs (@FuraLabs), a research and education firm on software security and reverse engineering. Co-founder and president of @HackingLliure, a non-profit association and hacking community. Speaker and trainer at several international security conferences.