Securing mobile apps: common vulnerabilities and fixes

In short: Most security holes in mobile apps trace back to a handful of recurring mistakes: sensitive data in unprotected storage, API keys in the app code, a backend that trusts the app blindly, and sloppy authentication. The most important rule of mobile app security is that anything on the device can be read. Secrets belong in the backend, tokens in the Keychain or Keystore, and every request is checked on the server.

Why mobile apps have their own security risks

A web application runs on your server; a mobile app runs on the user's device. Anyone who installs the app holds the complete package and can unpack, inspect and modify it with freely available tools. Add lost or stolen devices, insecure Wi-Fi and rooted or jailbroken phones.

The OWASP Mobile Top 10 and OWASP's MASVS verification standard are good references. They describe the typical risk areas and concrete test criteria. The points below cover the mistakes that come up most in practice.

The most common vulnerabilities

Insecure data storage

Tokens, passwords or personal data often end up in places not meant for them: UserDefaults on iOS, SharedPreferences on Android, or AsyncStorage in React Native. These stores are not encrypted and can be read with access to the device or a backup.

The fix is to use the system stores for secrets: the Keychain on iOS and the Android Keystore. In React Native you reach them through libraries such as expo-secure-store or react-native-keychain. Also, store only what the app really needs offline.

Secrets in the app code

API keys for payment providers, AI services or databases have no place in the app package. Even obfuscated, they can be extracted with modest effort. Every call that needs a secret key goes through your own backend, which holds the key and forwards the request after checking it.

A backend that trusts the app

A common fallacy: "The app doesn't allow that, so it can't happen." Any check that happens only in the app can be bypassed, because the API can be called directly without the app. Permissions, prices, limits and input validation must therefore be enforced on the server. Our article on web security fundamentals covers the basics, and they apply equally to mobile backends.

Weak authentication

Mobile apps should use OAuth 2.0 with PKCE through the system browser, not an embedded WebView in which the app could read credentials. Access tokens should be short-lived, refresh tokens stored securely and revocable on the server. Biometric unlock is convenient but does not replace server-side session checks. Details on tokens and sessions are in implementing authentication with OAuth, JWT and sessions.

Insecure communication

iOS enforces HTTPS by default through App Transport Security, and Android has blocked cleartext traffic by default since version 9. Problems start when developers switch these protections off for testing and forget to turn them back on. Certificate pinning adds protection against forged certificates but needs a plan for certificate rotation, or a renewal will lock out your own users.

Deep links and data leaks

Custom URL schemes such as myapp:// can be registered by any other app as well. For sensitive flows like login redirects or password resets, Universal Links on iOS and App Links on Android are safer, because they are bound to your domain. Also make sure logs, crash reports and the app switcher snapshot contain no sensitive data.

Building security into the development process

Security is hard to add afterwards. A lean approach works well: at the start of the project, clarify which data the app handles and how sensitive it is. That sets the requirements for storage, authentication and backend. Dependencies are scanned automatically for known vulnerabilities, and before major releases a penetration test by external specialists is worth it.

Apps with especially sensitive data, for example in finance or health, need further measures: app integrity checks via the Play Integrity API and Apple App Attest, detection of tampered devices and stricter session rules. Since mobile apps almost always process personal data, the GDPR belongs in the plan too. Our practical guide to GDPR-compliant software development helps with that.

Frequently asked questions (FAQ)

Is React Native less secure than native development?

Not inherently. The risks almost always lie in the implementation: storage, communication and backend. With the right libraries for secure storage and careful configuration, a React Native app reaches the same level of protection.

Is obfuscating the app code enough?

No. Obfuscation makes analysis harder but doesn't prevent it. It is an extra hurdle on top of the basic rule: keep secrets out of the app and check everything on the server.

How often should an app be security tested?

Automated checks of dependencies and code ideally run on every change. A manual security test is worth it before the first release and after major changes to authentication, payments or data storage.

Conclusion

Secure mobile apps come less from special tools than from a clear stance: the device is untrusted and the backend decides. If you keep secrets off the device, use the system stores and check every request on the server, you close most gaps before they open.

If you are planning an app or want to secure an existing one, talk to us about mobile app development.