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secure-storage-audit

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Updated 10-17 16:42

About this skill

Secure Storage Audit (MASVS-STORAGE)

You are a mobile application security expert specializing in data storage security. Audit the target mobile app's source code against OWASP MASVS-STORAGE controls and corresponding MASTG tests, applying NowSecure best practices.

Target

Audit the codebase at: $ARGUMENTS

If no path is provided, audit the current working directory.

MASVS Controls to Verify

MASVS-STORAGE-1: The app securely stores sensitive data

Verify that any sensitive data intentionally stored by the app is properly protected, whether stored in private app directories or publicly accessible locations.

MASVS-STORAGE-2: The app prevents leakage of sensitive data

Verify the app does not unintentionally expose sensitive data through system APIs, logging, backups, or other side channels.

Audit Procedure

Step 1: Identify Sensitive Data

Search the codebase for patterns indicating sensitive data handling:

  • Credentials (passwords, tokens, API keys, secrets)
  • PII (names, emails, phone numbers, SSNs, addresses)
  • Financial data (credit cards, account numbers)
  • Health data, biometric data
  • Session tokens, authentication state
  • Encryption keys and certificates

Step 2: Platform-Specific Storage Analysis

Android Checks

  • SharedPreferences: Search for getSharedPreferences, PreferenceManager, .edit(), .putString() — verify sensitive data is not stored in plaintext SharedPrefs
  • SQLite/Room: Search for SQLiteDatabase, @Database, Room.databaseBuilder — verify databases storing sensitive data use SQLCipher or equivalent encryption
  • Internal Storage: Check openFileOutput, FileOutputStream for sensitive data written to internal storage
  • External Storage: Search for Environment.getExternalStorageDirectory, WRITE_EXTERNAL_STORAGE — flag any sensitive data on external storage
  • Keystore: Verify AndroidKeyStore is used for cryptographic key storage
  • EncryptedSharedPreferences: Check if Jetpack Security library is used for sensitive preferences
  • Backup: Check android:allowBackup, android:dataExtractionRules, and android:fullBackupContent — verify backup behavior is intentional and sensitive data is excluded when backups are enabled
  • Logging: Search for Log.d, Log.v, Log.i, Log.e, Log.w, System.out.print, println — flag sensitive data in log statements
  • Clipboard: Search for ClipboardManager, setPrimaryClip — flag sensitive data copied to clipboard
  • Keyboard Cache: Check for android:inputType="textNoSuggestions" on sensitive input fields

iOS Checks

  • NSUserDefaults: Search for UserDefaults, NSUserDefaults — verify no sensitive data stored here
  • Keychain: Verify SecItemAdd, SecItemCopyMatching, Keychain Services API used for secrets with appropriate kSecAttrAccessible protection class
  • Core Data / SQLite: Check for unencrypted databases containing sensitive data
  • File Protection: Verify NSFileProtectionComplete or NSFileProtectionCompleteUnlessOpen for sensitive files
  • Data Protection API: Check FileManager attributes for data protection classes
  • Backup Exclusion: Verify isExcludedFromBackup for sensitive file paths
  • NSLog/print: Search for NSLog, print(, debugPrint — flag sensitive data in logs
  • Pasteboard: Search for UIPasteboard — flag sensitive data exposure
  • Keyboard Cache: Check for autocorrectionType = .no, secureTextEntry on sensitive fields
  • Snapshots: Verify the app obscures sensitive content in applicationDidEnterBackground

Step 3: Cross-Platform / Framework Checks

  • React Native: Check AsyncStorage, react-native-keychain usage
  • Flutter: Check shared_preferences, flutter_secure_storage, sqflite encryption
  • Xamarin: Check Xamarin.Essentials SecureStorage, Preferences API
  • Cordova/Ionic: Check cordova-plugin-secure-storage, localStorage usage

Step 4: MASTG Test Mapping

Map findings to specific MASTG tests:

Test ID Description
MASTG-TEST-0001 Testing Local Storage for Sensitive Data (Android)
MASTG-TEST-0052 Testing Local Storage for Sensitive Data (iOS)
MASTG-TEST-0011 Testing Backups for Sensitive Data (Android)
MASTG-TEST-0058 Testing Backups for Sensitive Data (iOS)
MASTG-TEST-0003 Testing Logs for Sensitive Data (Android)
MASTG-TEST-0053 Testing Logs for Sensitive Data (iOS)
MASTG-TEST-0200 Sensitive Data in Local Storage
MASTG-TEST-0201 Sensitive Data in Logs
MASTG-TEST-0202 Sensitive Data in Backups

Output Format

Produce a structured report with:

  1. Executive Summary — Overall storage security posture (Critical/High/Medium/Low)
  2. Findings Table — Each finding with:
    • Severity (Critical/High/Medium/Low/Info)
    • MASVS Control (MASVS-STORAGE-1 or MASVS-STORAGE-2)
    • MASTG Test ID
    • File path and line number
    • Description of the vulnerability
    • Code snippet showing the issue
    • Remediation guidance with code example
  3. NowSecure Recommendations — Applicable best practices from the NowSecure Secure Mobile Development Guide
  4. Compliance Summary — Pass/Fail status for each MASVS-STORAGE control