How to Secure a Mobile App: A Practical Checklist
Secure a mobile app by assuming the device and the app binary can be inspected by an attacker, and keeping anything valuable on a server you control. In practice: enforce authorization on every API call, keep secrets out of the app, store tokens in the iOS Keychain or Android Keystore, use HTTPS everywhere, vet third-party SDKs, and collect only the data you need. Use the OWASP MASVS as your checklist and test against it before each major release.
- Most serious mobile breaches happen at the backend API, not on the phone, so server-side authorization comes first.
- Anything shipped inside the app, including API keys, can be extracted; treat the app as a public client.
- Store tokens and sensitive data only in the platform's secure storage: Keychain on iOS, Keystore-backed storage on Android.
- Third-party SDKs run with your app's permissions; inventory them and remove what you do not need.
- OWASP MASVS and MASTG give you a free, recognized standard to build and test against.
The Steps
- Classify the data you handleList the data the app collects and stores, and mark what is sensitive: health, financial, location, identity documents, children's data. Sensitivity determines how much protection and testing you need.
- Lock down the backend APIAuthenticate every request and check authorization on the server for every object, so one user can never read another's records by changing an ID. Add rate limiting and logging.
- Keep secrets off the deviceNever embed private API keys, database credentials or admin tokens in the app. Route calls that need secrets through your own backend, and rotate any key that has shipped.
- Use secure storage for tokensStore session tokens in the iOS Keychain or Android Keystore-backed storage, never in plain preferences or logs. Avoid storing sensitive data on the device at all when you can.
- Enforce encrypted connectionsUse HTTPS with modern TLS for every connection, keep iOS App Transport Security on, and disable cleartext traffic on Android. Consider certificate pinning for high-risk apps.
- Harden authenticationOffer multi-factor authentication or passkeys for sensitive accounts, use short-lived access tokens with refresh tokens, and support biometric sign-in through the platform APIs rather than custom code.
- Vet and update dependenciesInventory every SDK and library, check what data each one collects, enable automated dependency scanning, and patch known vulnerabilities on a schedule.
- Test before every major releaseRun automated static and dynamic scans, and for sensitive apps commission a penetration test against OWASP MASVS. Fix high-severity findings before release and retest.
- Plan for incidentsDecide in advance who investigates, how you revoke tokens and keys, how you force an app update, and how you notify users and regulators if required.
Start With How Mobile Apps Actually Get Attacked
A mobile app runs on hardware you do not control. Anyone can download it, unpack the binary, read its strings, watch its network traffic and replay requests with modified values. That shapes the whole security approach: the app is a public client, and the server is where trust lives.
The OWASP Mobile Top 10 is a useful map of what goes wrong in practice. Its 2024 list leads with improper credential usage and inadequate supply chain security, followed by insecure authentication and authorization, insufficient input and output validation, insecure communication, inadequate privacy controls, insufficient binary protections, security misconfiguration, insecure data storage and insufficient cryptography. Several of these are really backend problems that show up through the app.
Using OWASP MASVS as Your Standard
The OWASP Mobile Application Security Verification Standard (MASVS) is the most widely referenced standard for mobile app security. It groups controls into eight areas:
- Storage: sensitive data is stored securely, or not at all.
- Crypto: cryptography uses current, well-vetted algorithms and keys are managed properly.
- Auth: authentication and authorization follow platform best practices.
- Network: data in transit is protected and server identity is verified.
- Platform: the app uses platform features such as permissions, deep links and WebViews safely.
- Code: dependencies are maintained and input is validated.
- Resilience: for higher-risk apps, resistance to tampering and reverse engineering.
- Privacy: data minimization, transparency and user control.
The companion OWASP Mobile Application Security Testing Guide (MASTG) explains how to test each control. Naming MASVS in your requirements and your contract gives your developers and testers a shared, objective target instead of a vague promise to "make it secure."
The Mistakes That Cause Real Incidents
Broken object-level authorization
The app asks for /api/orders/1042, and the server returns it without checking that order 1042 belongs to the logged-in user. Changing the number reveals other customers' orders. This is one of the most common serious flaws in app backends. Every endpoint must check ownership on the server, on every request.
Secrets in the app bundle
Payment provider secret keys, cloud credentials and AI provider API keys embedded in the app will be found. Use publishable keys that are designed to be public, and route anything privileged through your backend. If a secret has already shipped, rotate it.
Leaky third-party SDKs
Analytics, advertising and chat SDKs can collect more than you expect, and you are responsible for declaring that collection in Apple's privacy details and Google Play's Data safety form. Keep a written inventory of SDKs, what each collects and why it is there.
Sensitive data in logs and backups
Debug logs that print tokens or personal data, screenshots cached by the OS, and unencrypted local databases are frequent findings in security reviews. Strip sensitive logging from release builds and exclude sensitive files from backups.
Platform Tools Worth Using
- Secure storage: Keychain services on iOS and the Android Keystore system for keys and credentials.
- App integrity checks: Apple's App Attest and Google's Play Integrity API let your server check that requests come from a genuine copy of your app on a genuine device, which helps against bots and tampered clients.
- Passkeys and biometrics: platform passkey support and biometric prompts are safer than custom implementations. NIST's current digital identity guidance (SP 800-63B) is a good reference for password and multi-factor rules.
- Network security configuration: iOS App Transport Security and Android's network security config enforce HTTPS and can pin certificates.
Testing, Ownership and Regulated Data
Security is not a one-time audit. Build it into the process: code review, automated dependency and static analysis on every build, and a penetration test before major releases for apps that handle sensitive data. Assign one person to own security decisions and incident response, even in a small company.
If you handle health information, payment data or children's data, specific rules may apply, such as HIPAA, PCI DSS or COPPA. Get advice from a qualified professional on what applies to you; this page is practical guidance, not legal advice. Our healthcare page covers how this affects clinical apps, and the guide to accepting payments in an app explains how to keep card data out of your systems entirely.
Sources and Further Reading
We link to the primary documentation so you can verify the details yourself.
- Mobile Application Security Verification Standard (MASVS), OWASP
- Mobile Application Security Testing Guide (MASTG), OWASP
- OWASP Mobile Top 10, OWASP
- Security checklist, Android Developers
- Establishing your app's integrity, Apple Developer
- SP 800-63B-4: Authentication and Authenticator Management, NIST
Related Questions
Do small business apps really get attacked?
Yes. Most attacks are automated: bots scan for exposed keys, weak APIs and known vulnerabilities in common libraries, regardless of company size. A small app with customer data and a weak backend is an easy target. Basic controls such as server-side authorization and secure storage stop most of this.
Is certificate pinning necessary?
Not for every app. Pinning protects against attackers who can get a trusted certificate issued or installed, which matters most for banking, health and high-value apps. It also adds operational risk, because a badly managed certificate change can break the app. Decide based on your threat model.
How much does a mobile penetration test cost?
It varies with scope: one platform or two, the size of the API, and whether testers get source code. As a rough 2026 US ballpark, a focused test of a small app and its API often runs in the low five figures. Ask for testing mapped to OWASP MASVS and a free retest of fixes.
Can obfuscation protect my app?
Obfuscation and anti-tampering raise the effort needed to reverse engineer an app, which is worthwhile for apps with valuable logic or high fraud risk. They do not make secrets safe to embed, and they do not replace server-side controls. Treat them as an extra layer, not a foundation.