OWASP Top 10 for Mobile Apps: M9 – Reverse Engineering

Mobile applications have become an integral part of everyday life, shaping how businesses interact with customers, employees, and the world. However, with their growing prominence, mobile apps have also become prime targets for malicious actors seeking to exploit vulnerabilities. One of the most significant threats facing mobile app developers and security professionals is reverse engineering. This practice, as outlined in the OWASP (Open Web Application Security Project) Top 10 for mobile apps under category M9, poses a substantial risk to app security, data privacy, and business continuity.

In this blog post, we will explore the concept of reverse engineering in mobile apps, its risks, and how software developers and penetration testers can proactively mitigate the dangers it presents. Through detailed analysis and practical insights, this post aims to equip businesses and security professionals with the knowledge they need to safeguard their mobile applications from reverse engineering attacks, ensuring both security and business continuity.

What is Reverse Engineering in the Context of Mobile Apps?

Reverse engineering is the process of analysing a system or software to understand its components, functionality, and architecture. In the context of mobile apps, reverse engineering typically involves deconstructing an app’s compiled code to reveal its source code, data structures, and logic. The goal may be to identify vulnerabilities, extract sensitive data, or alter the app’s behaviour for malicious purposes.

For a mobile app developer, reverse engineering can be a nightmare. If attackers gain access to the underlying code of an app, they can:

Extract sensitive user data.
Discover security flaws and exploit them.
Bypass authentication mechanisms.
Modify app behaviour to introduce malicious features.

How Reverse Engineering Works

To understand how reverse engineering can affect mobile apps, it’s important to grasp the basic steps involved in the process:

Decompiling the App: Mobile apps are typically distributed in a binary format (APK for Android or IPA for iOS). Attackers can decompile these binaries to extract the app’s source code, which may reveal sensitive business logic or authentication protocols.
Analysing the Code: Once decompiled, attackers can analyse the app’s code and look for weaknesses, such as hardcoded credentials, encryption keys, or flaws in cryptographic algorithms.
Modifying the App: In some cases, attackers may not only extract the code but also alter it. They might change the app’s behaviour to steal data, bypass security measures, or install malicious payloads.
Repackaging and Re-distribution: After modifying the app, attackers can repackage it and distribute the altered version through unofficial channels, such as third-party app stores, potentially infecting users with malware or stealing sensitive data.

The Business Impact of Reverse Engineering

The implications of reverse engineering for a business can be devastating. It can lead to financial loss, brand damage, legal repercussions, and a loss of customer trust. Let’s break down the specific business impacts in more detail:

1. Data Breach Risks

Reverse engineering allows attackers to potentially access sensitive data, such as user credentials, private API keys, or financial information. A successful reverse engineering attack can expose this data, leading to breaches that affect both users and the company’s reputation. For example, if attackers extract user credentials stored insecurely in the app, they may use this information for identity theft or fraud.

2. Intellectual Property Theft

Many mobile applications are built with proprietary business logic, algorithms, or unique features that provide a competitive edge. Reverse engineering allows attackers to steal this intellectual property (IP), which can be used by competitors or even sold on underground marketplaces. If a competitor can replicate your app’s functionality by reverse-engineering your code, you may lose market advantage.

3. Business Continuity and Operational Disruption

If attackers are able to modify an app’s functionality, they can introduce vulnerabilities or backdoors that allow future attacks. For example, attackers may inject malicious code that can disrupt app performance or steal data at a later stage, creating operational disruptions. These types of attacks can cause extended downtime or loss of service, significantly impacting business continuity.

4. Brand and Customer Trust Erosion

Consumers and businesses place great trust in apps to protect their data. If an app becomes the target of reverse engineering, and sensitive data is compromised or misused, the brand’s reputation will suffer. This can lead to a loss of customers, decreased revenue, and an increased burden on the business to rebuild trust through costly public relations campaigns or legal actions.

5. Legal and Regulatory Consequences

Depending on the jurisdiction, businesses can face legal consequences for failing to protect user data or intellectual property. For example, the General Data Protection Regulation (GDPR) in the European Union imposes heavy fines on companies that fail to adequately safeguard personal data. If reverse engineering leads to a data breach, businesses can face significant penalties, especially if they have not taken proper measures to protect against reverse engineering in the first place.

How Reverse Engineering Threatens Mobile App Security

Reverse engineering is a serious threat to mobile app security for several reasons. It opens up numerous attack vectors that can compromise the integrity and confidentiality of both the app and its users. Let’s explore some of the specific security risks associated with reverse engineering:

1. Exposure of Hardcoded Secrets

One of the most common mistakes in mobile app development is storing sensitive information, such as API keys, passwords, or encryption keys, directly in the app’s code. Reverse engineering allows attackers to retrieve this hardcoded information and gain unauthorised access to critical services or data. This can lead to full-scale account takeover, data theft, or denial of service.

2. Bypassing Authentication

Many mobile apps rely on various authentication mechanisms, such as token-based authentication or biometric identification. However, attackers can reverse engineer these mechanisms to find ways to bypass authentication. For example, an attacker might intercept communication between the app and the server, gaining access to accounts without ever needing to enter a password.

3. Manipulation of App Behaviour

Once an attacker has access to the app’s code, they can alter how the app functions. This could involve:

Removing security checks, such as verifying device integrity or location.
Changing app logic to allow unauthorised access to premium features.
Injecting malicious code to steal user data or perform other harmful activities.

4. Tampering with Communication

Reverse engineering can also allow attackers to modify network traffic between the mobile app and the backend servers. This can lead to attacks like Man-in-the-Middle (MitM) attacks, where attackers intercept and modify data exchanged between the app and its backend services, potentially gaining access to sensitive data or introducing malicious payloads.

5. Injection of Malware

With full access to the app’s code, attackers can inject malware into the app and repackage it. The modified app can then be redistributed through unofficial channels, targeting unsuspecting users. Once installed, the malware may:

Harvest personal information from the device.
Record user interactions.
Exploit system vulnerabilities to gain deeper access to the device.

Mitigating Reverse Engineering Risks: A Developer’s Guide

Given the severe risks associated with reverse engineering, it is essential for developers and penetration testers to implement strategies to protect their mobile applications. Below, we’ll explore practical techniques and tools that can help mitigate the risk of reverse engineering.

1. Code Obfuscation

Code obfuscation is one of the most effective ways to make reverse engineering more difficult. By obfuscating the app’s code, developers make it harder for attackers to understand the logic and functionality of the app. Obfuscation tools modify the app’s code by renaming variables, methods, and classes into meaningless names, making the code less readable and harder to reverse-engineer.

However, it is important to note that obfuscation does not prevent reverse engineering entirely; it only makes the process more time-consuming and challenging for attackers.

2. Encryption and Secure Storage

Storing sensitive data securely is crucial to preventing data leakage through reverse engineering. Developers should use strong encryption techniques to protect data both at rest (on the device) and in transit (over the network). Sensitive information such as passwords, API keys, and tokens should never be stored in plaintext.

Additionally, consider using secure storage mechanisms provided by the mobile platform (e.g., iOS’s Keychain or Android’s Keystore) to store sensitive data securely.

3. Server-Side Validation

To ensure that attackers cannot manipulate the app’s functionality, critical validation should be performed server-side rather than on the client side. This includes validating API requests, authentication tokens, and user input. By relying on server-side validation, developers can reduce the risk of attacks such as bypassing authentication or injecting malicious code.

4. Code Signing and Integrity Checks

Implement code signing and integrity checks to ensure that the app has not been tampered with. Mobile operating systems (iOS and Android) support code signing, which allows developers to sign their apps with a certificate. This ensures that the app has not been altered since it was signed, helping to prevent attackers from distributing modified versions of the app.

5. Use of Secure Communication Protocols

All communication between the mobile app and backend services should be encrypted using secure protocols like HTTPS (SSL/TLS). This prevents attackers from intercepting or tampering with data exchanged between the app and the server. Additionally, developers should use certificate pinning to prevent Miscreants-in-the-Middle (MitM) attacks.

Certificate Pinning

Certificate pinning helps prevent Miscreants-in-the-Middle (MitM) attacks by binding the app to a specific server certificate. This ensures that even if the attacker intercepts the app’s traffic, they cannot impersonate the server.

6. Application Runtime Protection

Tools like ProGuard and AppShield can be used to protect the app at runtime. These tools detect when the app is being reverse-engineered or debugged and can take action to prevent the attack, such as terminating the app or obfuscating certain parts of the code during runtime.

Runtime Application Self-Protection (RASP)

RASP solutions can detect and prevent reverse engineering in real-time. These solutions monitor the app’s behaviour and provide an extra layer of protection against runtime manipulation and tampering.

Understanding the Process Strategies

Reverse engineering is an essential aspect of security analysis, particularly in the realm of software and mobile application security. It involves systematically deconstructing software or hardware systems to understand their design, functionality, and potential vulnerabilities. While reverse engineering can be a powerful tool for improving security through penetration testing, it can also be exploited by malicious actors to compromise systems. For developers and security professionals, understanding the methodology of reverse engineering is crucial for identifying weaknesses and implementing effective protections.

In this post, we will explore the reverse engineering methodology, focusing on the process, tools, and strategies used to reverse-engineer mobile applications. We’ll also highlight the importance of secure development practices and provide insights into how businesses and penetration testers can protect applications from reverse engineering.

1. Overview of Reverse Engineering

Reverse engineering is typically performed on compiled software or hardware components. In software, it involves deconstructing a program to reveal its source code or to analyse its behaviour, algorithms, and architecture. For mobile apps, reverse engineering allows security professionals to inspect an app’s code, identify vulnerabilities, and determine how an app interacts with its environment.

While reverse engineering has legitimate uses in debugging, security analysis, and software maintenance, it can also be used maliciously. Attackers use reverse engineering to find exploits, steal intellectual property, or deploy malware. Understanding the process is vital for both developers and penetration testers to identify potential risks and safeguard mobile applications against reverse engineering attacks.

2. Stages of Reverse Engineering for Mobile Apps

Reverse engineering can be broken down into several stages. These stages may vary depending on the target (Android, iOS, etc.) and the goal of the reverse engineering process. Below are the typical stages involved in reverse engineering a mobile application:

2.1. Initial Assessment and Data Collection

Before diving into reverse engineering, a comprehensive understanding of the target is essential. The initial assessment involves gathering as much information as possible about the mobile app, including:

App version: Knowing the app version helps determine if any updates or patches have been applied.
File format: Mobile apps are packaged in formats like APK (Android) or IPA (iOS), and identifying these formats helps in choosing the correct tools for decompiling or unpacking the files.
Permissions and APIs: Analysing what permissions the app requests, such as access to location, camera, or microphone, provides insight into the app’s functionality and potential security risks.

At this stage, the goal is to collect basic data to help guide the rest of the process.

2.2. Decompiling and Unpacking

Once the app is collected, the next step is to decompile or unpack the app’s binary file (APK for Android or IPA for iOS). This is where tools such as APKTool, jadx (for Android), and class-dump (for iOS) are commonly used.

Android (APK): Tools like APKTool are used to disassemble the APK, revealing the resources, code, and manifest file. This helps in understanding the app’s logic and identifying any hardcoded secrets or potential vulnerabilities in the code.
iOS (IPA): For iOS apps, tools like class-dump or IDA Pro are used to extract classes and methods from the binary. iOS apps are typically more secure out-of-the-box, so reverse engineers might need to jailbreak the device or bypass certain security mechanisms before analysing the app.

This stage results in a collection of resources, including source code, configuration files, and other assets that can be further explored.

2.3. Code Analysis

In this stage, the reverse engineer inspects the decompiled source code to understand the app’s functionality and identify potential weaknesses. Key tasks include:

Identifying hardcoded data: Developers often store sensitive information, such as API keys, passwords, and encryption keys, directly in the app’s code. Reverse engineers look for this information to gain unauthorised access.
Examining code flow: Understanding how the app operates and processes data can help pinpoint flaws, such as weak authentication mechanisms or vulnerabilities in communication protocols.
Looking for insecure storage: If the app stores sensitive data (e.g., passwords) in plaintext or uses weak encryption, it becomes a prime target for exploitation.
Static analysis: This process involves examining the app’s code without executing it, looking for logical errors or vulnerabilities.

Tools such as JD-GUI (for Java-based Android apps) or Ghidra (a general-purpose disassembler) may be employed for deep code analysis.

2.4. Dynamic Analysis

Dynamic analysis is the process of running the app in a controlled environment to observe its behaviour during execution. This stage helps identify runtime vulnerabilities, such as:

Interception of API calls: By using tools like Burp Suite or Frida, penetration testers can intercept and modify API calls between the app and the server to understand how data is transmitted and identify weak points.
Memory inspection: By monitoring the app’s memory space during runtime, attackers can find unencrypted data or other information that is not stored securely.
Identifying runtime behaviour: Understanding how the app interacts with the system in real-time is crucial for detecting flaws such as privilege escalation, lack of input validation, or the use of outdated libraries.

In dynamic analysis, the goal is to observe the app’s execution in a real-world environment to identify runtime vulnerabilities that may not be apparent from static code alone.

2.5. Reverse Engineering the Communication Channels

Another critical aspect of reverse engineering mobile apps is examining how the app communicates with backend servers. Attackers will often focus on the following:

API communication: Apps often rely on REST APIs to communicate with the server. Reverse engineers will examine these API endpoints to find potential security holes, such as unencrypted communication or poorly implemented authentication.
Network traffic analysis: Tools like Wireshark or mitmproxy are used to capture and analyse network traffic between the app and the server. If sensitive data is transmitted without proper encryption (e.g., over HTTP instead of HTTPS), this can expose the app to Man-in-the-Middle (MitM) attacks.
Examining third-party libraries: Many apps use third-party libraries, and reverse engineers will inspect these to ensure there are no security flaws that could be exploited.

3. Common Tools Used in Reverse Engineering Mobile Apps

Several tools are commonly employed in the reverse engineering process, each serving a different purpose. Below is a list of the most popular tools used in reverse engineering mobile apps:

3.1. For Android:

APKTool: Used to decompile Android APK files and decode resources.
JD-GUI: A tool for decompiling Java bytecode to Java source code.
Jadx: A decompiler for Android APK files that converts DEX (Dalvik Executable) files into readable Java code.
Frida: A dynamic analysis tool that allows penetration testers to intercept and modify live application code during runtime.

3.2. For iOS:

class-dump: Used to extract class definitions from iOS applications.
IDA Pro: A powerful disassembler used for deep code analysis, including binary analysis for both iOS and Android.
Hopper Disassembler: A reverse engineering tool for Mac OS and iOS apps, capable of performing static and dynamic analysis.

3.3. For Both Android and iOS:

Wireshark: A network protocol analyser for monitoring network traffic.
Burp Suite: A popular tool for intercepting HTTP/S requests and responses, commonly used for web application penetration testing.
Ghidra: A software reverse engineering tool developed by the NSA, useful for decompiling and analysing binary files.

Final Thoughts

Reverse engineering is one of the most formidable threats to mobile app security. For software developers and penetration testers, understanding the risks associated with reverse engineering and adopting effective countermeasures is critical. By implementing techniques such as code obfuscation, secure data storage, server-side validation, and runtime protection, businesses can significantly reduce the risk of reverse engineering attacks, safeguarding both their intellectual property and user data.

As mobile app usage continues to rise, it is essential to remain vigilant and proactive in securing applications against reverse engineering. By doing so, companies not only protect their business but also maintain the trust and confidence of their customers, ensuring long-term success in an increasingly digital world.

Reverse engineering is a powerful technique used by security researchers and attackers alike to understand and exploit mobile apps. By following a systematic methodology, attackers can uncover vulnerabilities that threaten an app’s security, data privacy, and business continuity. However, developers can take proactive steps to defend

Penetration testers play a vital role in identifying vulnerabilities in mobile applications, and through the use of modern tools and techniques, they can simulate reverse engineering attacks to identify weak points before malicious actors can exploit them. As mobile applications continue to dominate the digital landscape, ensuring their security through effective reverse engineering countermeasures is crucial for protecting businesses, users, and data from emerging threats.