Reverse engineering
In today's interconnected digital landscape, understanding the inner workings of software and computer systems in general is paramount for both innovation and security. While most development focuses on building forward, a critical practice involves looking backward: reverse engineering. Often seen as a mysterious or purely offensive technique, reverse engineering is, in fact, an indispensable tool for cybersecurity professionals and is foundational to modern digital defense.
What is reverse engineering?
Just out of curiosity, a child may take a device and disassemble it, possibly wondering what elements are inside and how they come together to work. Something similar can be done by an adult in a workshop, but, for example, with the intention of repairing an engine that, for some unknown reason, has stopped working. We can also mention the woman who, in her workplace, has the mission of deconstructing the program that others had worked on before, just to renew and improve some of its performance features. All of them have applied what is known as reverse engineering.
Reverse engineering is a process of deconstruction. It is a matter of reversing the steps of development in order to analyze and obtain knowledge of anything engineered and elaborated by human beings, primarily. That thing can be a chemical substance, a machine, a software code, or another type of object. Reverse engineering seeks to reveal and determine the innermost details, the components and their relationships, and ultimately to discover how the object in question was designed and produced.
Here are some of the reasons why reverse engineering is employed:
Information on a product: Documentation may have been lost, is inaccessible, or simply never existed, and there is no contact with the producer.
Analysis of a product: Knowing how it works, what components it has, defining costs, and identifying possible copyright violations.
An update or correction of the product's functioning.
Security auditing or assessment of a product.
Creation of duplicates of a product without a license.
Competition issue: Understanding what competitors do and what characterizes their products.
Simple curiosity and learning purposes about the structure of a product.
In the context of information technology, we can apply reverse engineering to hardware or software. In this case, we focus on software reverse engineering. Basically, this engineering takes a "final" software product—often a compiled binary or executable file—and works backward to uncover its underlying logic, structure, and functionality—especially when the original design documentation or source code is missing or inaccessible—usually for the purpose of repairing or improving it. This process is said to have emerged from software maintenance and support, largely from malware analysis.
Why is reverse engineering essential in cybersecurity?
While reverse engineering has broader applications (e.g., product duplication, interoperability, legacy system modernization), its role in cybersecurity is unequivocally preventive and defensive. It serves mainly as a fundamental mechanism for vulnerability discovery and malware analysis. In other words, in the realm of security, software reverse engineering transforms from a general analytical tool into a necessary technique for protecting digital assets.
Malware analysis and threat intelligence
The most common application of reverse engineering in cybersecurity is the dissection of malicious software. Threat actors frequently employ obfuscation and encryption techniques to conceal the true nature of their code, making traditional security analysis ineffective. Reverse engineers can effectively unmask these threats.
By taking apart malware binaries, analysts can precisely determine:
Payload and objectives: What the malware is designed to do (e.g., steal data, encrypt files, install a backdoor).
Evasion techniques: How the malicious code hides from antivirus software or operates discreetly within a compromised system.
Command-and-control (C2) structure: How it communicates with its operators to receive new instructions or exfiltrate data.
Indicators of compromise (IOCs): Critical data points (file names, registry keys, network addresses) that bolster an organization's incident response efforts and help develop definitive signatures and patches.
This detailed, low-level understanding is vital for creating effective countermeasures, such as new antivirus signatures, firewall rules, and system patches.
Vulnerability discovery and auditing
Reverse engineering is crucial in vulnerability research, where security experts proactively hunt for flaws that attackers might exploit. By scrutinizing applications—especially those that handle sensitive data or are internet-facing—at the assembly or source code level, professionals can uncover weaknesses that are often invisible from external black-box testing. This includes identifying:
Insecure coding practices
Hidden backdoors or hardcoded credentials
Flaws in proprietary encryption algorithms
Buffer overflows and other memory corruption issues
Identifying these security gaps before malicious actors do allows for the timely development of fixes and patches, significantly enhancing the software's security posture.
Digital forensics and incident response
Following a security incident or data breach, reverse engineering plays a key role in digital forensics. Experts use the technique to understand the full scope of an attack by
dissecting software artifacts or modified system files left behind by an attacker;
reconstructing the attacker's actions and methods to trace the attack’s source;
gathering legally admissible evidence related to the breach.
On the basis of these analyses, the organizations affected and stakeholders can receive recommendations and implement preventive and reactive measures in the event of possible future incidents, in order to guarantee their own security and that of their customers or users.
The phases of software reverse engineering
We can separate software reverse engineering into two main stages: The first one can be seen as a large-scale observation or high-level overview to determine the general structure, and sometimes areas of special interest, of the software under analysis. This stage implies the use of various tools and several services of the operating system. These tools and services enable the acquisition of information, tracking inputs and outputs, and inspecting executables, among other things. The second stage is deeper and more granular, oriented to code fragments to understand them in their structure and functionality.
Here is a more detailed, commonly recognized three-step process that is applied across most reverse engineering efforts:
1. Information extraction and static analysis
This initial phase focuses on gathering all possible data about the software without executing it (static analysis).
Asset discovery: Identifying the file type, compiling tools, embedded resources, and relevant metadata (e.g., timestamps, integrity checks).
Disassembly: The executable is fed into a disassembler to convert the raw machine code (binary or hexadecimal code) into assembly language, a human-readable, low-level representation of processor instructions.
Decompilation: The analyst uses a decompiler to transform the compiled code (either binary or assembly) into a higher-level, even more understandable, language, often C or C++ pseudocode. While this code isn't the original source, it provides a much clearer view of the program's logic, control flow, and data structures.
This phase aims to create a conceptual model of the software, often through data flow diagrams or structure charts, which map how the different parts of the program interact.
2. Dynamic analysis and observation
This phase involves running the program in a controlled and isolated environment (a sandbox or virtual machine) to observe its behavior in real-time.
Debugging: A debugger is used to execute the code line-by-line, set breakpoints at critical points, and inspect the program's state, including the contents of memory registers and variables, at various stages. This is crucial for understanding how the code handles data, manipulates the system, and interacts with external services.
Network monitoring: Tools are used to capture and analyze network traffic generated by the application, which is essential for understanding communication protocols, command-and-control channels, and data exfiltration attempts.
This phase adds runtime context to the static findings, verifying whether potential code-level vulnerabilities are actually exploitable in a live environment.
3. Reconstruction, documentation, and mitigation
The final phase consolidates all the information to achieve the expected security goals.
Reconstruction: The analyzed data is used to fully reconstruct the software's logic and design, providing a detailed understanding of its security posture.
Documentation: All findings, including vulnerabilities, malware mechanisms, and potential attack paths, are meticulously documented.
Mitigation: This knowledge is translated into actionable security measures, such as developing patches, creating detection signatures, or implementing new defensive coding practices.
Essential toolset for reverse engineering
Reverse engineers rely on a specific suite of tools—many of which were not designed directly for reverse engineering—that aid in translating machine instructions into human-understandable logic and observing the program's behavior in a controlled, live environment for dynamic analysis.
Disassemblers
One of the main tools for software reverse engineering is the disassembler, which develops a process contrary to an assembler, and which will be different depending on the platform on which it is used. The disassembler translates machine language (input) to assembly language (output) for the entire program or parts of it. Examples:
IDA Pro (interactive disassembler): Widely considered the industry standard, IDA offers robust static analysis and supports a vast array of processors and executable formats, often extended with the Hex-Rays Decompiler.
Ghidra: Developed by the NSA (National Security Agency) and released to the public, Ghidra is a free and open-source tool that offers a comprehensive suite of reverse engineering capabilities, including a disassembler and decompiler, making it highly popular among security researchers.
Radare2 (r2): A powerful, command-line-driven framework known for its portability and abilities to handle large binaries and explore possible execution paths within static code.
Debuggers
As an expansion of the disassembler’s work, and in some reverse engineering tasks as the only necessary tool, we have the debugger. With this kind of tool, over the disassembled code, we can establish breakpoints—and check the current state of the program within them—in locations of interest, go through the code running line by line in its analysis, and even make edits at run time. In other words, unlike the disassembler, the debugger does not work on static program code, but allows us to observe the behavior of the program while it is running, at a pace suitable for human perception, with pauses in execution as necessary. Examples:
x64dbg/OllyDbg: Popular open-source debuggers for dynamic analysis on Windows, often used to examine system calls and malware behavior in real-time.
WinDbg: Microsoft's powerful debugger, essential for low-level Windows kernel and application analysis.
Frida/Xposed: Dynamic instrumentation toolkits used for runtime manipulation and debugging of mobile applications (Android/iOS).
Decompilers
A decompiler tries to recreate the original source code in a high-level language through the analysis of the binary code or sometimes the assembly language. Nevertheless, the information obtained is complex to understand. High-level concepts like classes, arrays, sets, and lists may not be easily recreated. And comments and variable names may have been completely lost (omitted during compilation), even the name of the high-level language used. Still, the decompiler is valuable and useful because it reveals all the basic information about the operation of the program. Examples:
Hex-Rays decompiler: The decompiler component for IDA Pro.
JADX/JEB decompiler: Tools specializing in decompiling Android's Dalvik Executable (DEX) files back into readable Java code.
Other utility tools
Hex editors (e.g., WinHex, Hiew): Used to view and manually edit raw binary data at the byte level.
Sandboxes (e.g., Cuckoo, Any.Run): Automated environments designed to safely execute malicious software for behavior analysis and reporting.
Network analyzers (e.g., Wireshark): Essential for capturing and inspecting network traffic to understand C2 communications or protocol flaws.
Unpackers: Tools used to decompress or decrypt packed/obfuscated files, which are common tactics employed by malware.
Knowledge required to become a reverse engineer
Software reverse engineering is a highly specialized skill that requires a deep and multifaceted understanding of computer science fundamentals, far beyond standard application development. A successful reverse engineer must possess proficiency in:
Low-level programming languages
A broad understanding of assembly language is non-negotiable. Since disassemblers translate binaries into assembly code, the analyst must be able to read and interpret what the processor is doing at the most fundamental level—how it handles memory, registers, and execution flow. This also necessitates strong knowledge of high-level languages like C and C++, as many operating systems and critical applications are written in these languages.
Operating system and hardware architecture
Reverse engineering requires intimate knowledge of how different operating systems (Windows, Linux, macOS) work and how software interacts with the OS kernel and hardware. Analysts need to understand system calls, memory management, process creation, and inter-process communication to trace a program’s behavior accurately and identify how malware may be exploiting system vulnerabilities.
Obfuscation, anti-debugging, and cryptography
Threat actors are constantly working to impede reverse engineering efforts. Therefore, the reverse engineer must be skilled in identifying and bypassing these countermeasures:
Code obfuscation: techniques like packing, encryption, and confusing control flow, designed to deliberately make the code difficult to read and understand during static analysis.
Anti-debugging: code that actively detects if it is running inside a debugger or sandbox and then alters its execution or terminates to conceal its true purpose and prevent dynamic analysis.
Cryptography: the use of strong or proprietary cryptographic algorithms to protect the malware's most sensitive data (payloads) and encrypt its C2 communication streams, making them unreadable without the correct key or successful reverse engineering.
Scripting and automation
While the core analysis is manual, scripting languages like Python are crucial for automating repetitive tasks, analyzing large log files, and extending the functionality of tools like Ghidra or IDA Pro through custom plugins and scripts.
Ethical, legal, and business implications of reverse engineering
Reverse engineering is a double-edged sword: it is a technique used to protect systems, but it can also be leveraged for malicious or ethically questionable purposes.
The dual nature of reverse engineering
Software reverse engineering can be useful for modifying application structures, altering code, adding or removing commands, and changing functions, thus affecting their logical flow. From the security area, the software reverse engineering provides techniques for hacking, whether it is malicious or ethical. In other words, it is useful to do damage or to generate protection and prevent it.
On the positive side, reverse engineering has made it possible to detect flaws and vulnerabilities in, for example, encryption algorithms. Also, to analyze the behavior and properties of malware in test systems or already infected foreign systems (hence the development of antivirus software). Furthermore, it has enabled the prevention of the piracy of programs and the information contained in them, thus protecting digital rights.
On the negative side, through software reverse engineering, criminals can find vulnerabilities in systems, and well… take advantage of them. Malicious actors use reverse engineering to bypass license checks, gain unfair competitive advantage by stealing proprietary algorithms, or develop zero-day exploits.
Legal and ethical considerations
The line between ethical and unethical reverse engineering is often determined by intent and local law.
Intellectual property: Many commercial software license agreements (EULAs) explicitly prohibit reverse engineering. The primary concern is protecting proprietary algorithms and source code. However, many legal systems, such as the U.S. Digital Millennium Copyright Act (DMCA), contain exceptions that permit reverse engineering for legitimate goals like:
Interoperability: making a product compatible with another system
Security research: finding and reporting vulnerabilities (ethical hacking or pentesting)
Fair use: academic research and education
Ethics: The ethics of reverse engineering revolve around the principle of respecting the original creator's intellectual property versus the greater good of public safety. Ethical reverse engineering is always conducted with explicit permission from the owner of the system being analyzed or is focused solely on assessing publicly available malware for defensive purposes.
Our stance: ethical hacking and security assurance
At Fluid Attacks, our security experts or pentesters work within an ethical hacking framework, meaning they always have our clients' consent and act in their best interests in terms of privacy, integrity, and security. As part of our comprehensive Continuous Hacking solution, reverse engineering is one of the three fundamental manual vulnerability detection techniques we use, along with penetration testing as a service (PTaaS) and secure code review (SCR).
In our team, we leverage reverse engineering to perform in-depth analyses on various types of software, dissecting the compiled code to ensure that secrets or logic vulnerabilities that other types of evaluations might overlook do not remain hidden. All this is done with the aim of suggesting to our clients' development and security teams the implementation of clear vulnerability remediation guidelines or other appropriate preventive measures against possible future cyberattacks.
Conclusions
Reverse engineering, when applied ethically, is one of the most powerful analytical tools available to the cybersecurity community. It moves security beyond surface-level checks, enabling a deep, code-to-metal understanding of how digital systems truly function.
By dissecting threats and deconstructing applications at the binary level, reverse engineers transform fragmented code into actionable intelligence, allowing organizations to develop highly precise defenses against the most sophisticated cyber threats. For any organization committed to building robust and resilient software, investing in the expertise and tools necessary for reverse engineering is not optional—it is a strategic necessity for mastering the digital threat landscape.
Contact us and learn more about Fluid Attacks' AppSec solutions.
