How Secure Are Flutter Apps?

What is Flutter?

Flutter is an open source framework for mobile application development developed by Google, and is based on the Dart language. It can be run on various platforms such as Android and iOS, as well as the web, desktop, and IoT devices, and is optimized for cross-platform development that supports multiple environments with a single code. Due to its fast development speed, high scalability, rich UI components, and animation support, it has recently established itself as a leader in mobile app development, and is being chosen by many developers and companies.

Flutter App Security: Is It Really Worse Than Native Apps?

However, Flutter has some areas where security is lacking with only the basic settings, and these are often overlooked. In particular, security in the mobile environment is not an option but a necessity, but security considerations are often neglected due to the focus on convenience and speed of development.
Many developers may have the prejudice that "Flutter is cross-platform, so security is weak," but in reality, depending on the method and attitude of security implementation, a level of security comparable to that of native apps can be implemented. What is important is not the framework itself, but how security is applied.
Flutter apps can basically provide a similar level of security to native (Android/iOS) apps, but additional measures are required for code protection, data storage, and network security. In particular, they can be vulnerable to security threats such as code leakage through decompilation, unencrypted data storage, and man-in-the-middle attacks (MITM).

In addition, recent mobile app hacking techniques are becoming increasingly sophisticated, going beyond simple code analysis to memory manipulation, network sniffing, and the use of automated tools. In particular, Flutter apps have AOT compilation and structural simplicity, so attackers can quickly figure out the code structure when reverse engineering, and traditional security methods alone have limitations in responding. In this blog, we will analyze what vulnerabilities Flutter apps have in terms of security and take a closer look at the security enhancement methods that must be applied to develop a secure app.

1. Security Vulnerabilities in Flutter Apps: Comparative Analysis with Native Apps

1) Code protection issues: Risk of decompiling Dart code

Dart, the base language of Flutter, has the advantage and disadvantage of being simple. It is intuitively easy to use, but for experienced developers, it is not as complicated as languages ​​like Kotlin or Swift. Dart is converted to native code through AOT (Ahead-of-Time) compilation during the build process. However, during this process, there is a risk that some metadata and code structures may be exposed through reverse engineering. In particular, if sensitive information such as authentication logic or API keys are included in the client code, there is a risk that they can be easily exposed through decompilation. Therefore, it is recommended to apply code obfuscation (--obfuscate, --split-debug-info) and protect the core security logic by separating it into native code on the Android or iOS side.

2) Data storage vulnerability: Data storage is basically unencrypted.

In order to store information in Flutter, the SharedPreferences package is commonly used. However, this method does not support encryption by default, so there is a risk that sensitive information such as tokens, login information, and personal information of users may be easily exposed. Therefore, when storing sensitive data such as login information or user identification values ​​(ID), it is recommended to store them using SecureStorage, and it is recommended to consider a structure in which sensitive information is managed on a server rather than locally if possible.

3) Network security issues: MITM attacks are possible if SSL Pinning is not applied.

Flutter apps usually use libraries like http or dio to process network requests when exchanging data with servers. Basic SSL authentication is applied during this process, but since the server certificate is not thoroughly checked for forgery, there is a risk of a man-in-the-middle attack (MITM) in which an attacker intercepts communication with a fake server. Especially when handling sensitive data such as login, payment, and user information, a secure connection between the app and the server is very important. To this end, by applying SSL Pinning, you can strengthen security by restricting the app to communicate only with normal servers with trusted certificates. It can be easily implemented in Flutter with dio settings or a dedicated plugin.

4) Lack of security validation for packages (plugins)

When developing Flutter apps, using various packages (plugins) can make development much easier, but using unverified packages can be dangerous. Some packages may require excessive permissions or may transmit sensitive data to the outside. Therefore, even for packages registered on pub.dev, you must check the rating, whether they have been recently updated, and whether they are open source code. If possible, it is safer to preferentially use packages provided by trusted developers or officially provided.

2. How to strengthen Flutter app security with LIAPP

Flutter is convenient because it focuses on rapid development and UI-centric convenience, but in terms of security, it requires more careful management than native apps. As we have seen above, there is a risk of code exposure due to the characteristics of Dart code, and the high dependency on external packages can lead to unintended information leaks or security vulnerabilities. In addition, due to the cross-platform nature, there is a structure that makes it difficult to respond in detail to all security situations. To supplement these security vulnerabilities, you can apply powerful security functions to your app without additional development by utilizing the professional mobile app security service LIAPP.

1) Critical code obfuscation & encryption

Apps made with Flutter are based on Dart code and are compiled and distributed as native library files such as libapp.so. These native files may contain actual business logic or sensitive processing, so there is a risk that the internal implementation can be stolen through reverse engineering.
Usually, data encryption is applied through the encrypt package in Flutter, but if the encryption logic and key exist inside the client, there is still a security vulnerability. Therefore, simple logic-level encryption is not enough, and measures to protect the native library itself are needed.
LIAPP can further strengthen security by providing integrity verification and anti-forgery prevention for the .so file containing the core logic of the Flutter app through the Native Library Protection function in addition to Java source obfuscation. If the existing Java code obfuscation function is also applied in parallel, a security environment that can respond to both native and hybrid structures is built.

2) Data protection through various security features

Flutter's flutter_secure_storage and sqflite_sqlcipher packages are effective in encrypting and storing sensitive data within the app, but the encryption logic or key itself can still be exposed, making complete protection difficult. However, using a security solution such as LIAPP can enhance the overall security of the app by providing security features such as memory protection, debugging detection and blocking, rooting detection, virtual machine detection, and hacking tool detection. LIAPP goes beyond simple data encryption to protect the entire app execution environment, helping to respond to advanced hacking techniques such as reverse engineering and memory tampering. In particular, it can prevent the leakage of logic or encryption keys containing sensitive information, which is a major advantage in that it can enhance the security of the execution unit that is difficult for developers to implement directly.

3) Supplementing SSL Pinning from a network security perspective

Applying SSL Pinning to network requests in Flutter can prevent basic MITM attacks, but open source code-based SSL Pinning is difficult to consider as a complete security measure because various bypass methods are already known. Therefore, to strengthen Flutter network security, it is more effective to utilize LIAPP's SSL Pinning function to dynamically verify certificates during app execution and detect and block malicious proxies or abnormal network environments.

External packages used in Flutter are useful for accelerating development, but they can be vulnerable to security vulnerabilities, so caution is required. When selecting a package, it is recommended to check the GitHub star rating, recent commits, maintenance status, etc., and review suspicious permission requests or internal logic. It is also important to regularly check for package updates and use the latest version with security patches. Introducing a vulnerability scanner to the CI/CD pipeline will help detect security risks in advance. And most importantly, it is important not to rely solely on security-related packages, but to introduce a specialized security solution such as LIAPP to protect the integrity of the entire app and its execution environment. This will also prevent security incidents caused by package vulnerabilities in advance.

If you consistently manage these practices, your Flutter app can also build a strong security environment that is superior to that of native apps.

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