android-legacy-security

name	android-legacy-security
description	Standards for Intents, WebViews, and FileProvider. Use when securing Intent handling, WebViews, or FileProvider access in Android. (triggers: **/*Activity.kt, **/*WebView*.kt, AndroidManifest.xml, Intent, WebView, FileProvider, javaScriptEnabled)

Android Legacy Security Standards

Priority: P0

Implementation Guidelines

Intents & Components

• Visibility: Set android:exported="false" in the Manifest for all internal Activities/Services unless explicitly needed for deep links or external integration.
• Intents: Verify resolveActivity before starting implicit intents. Use LocalBroadcastManager (legacy) or SharedFlow/StateFlow for internal communication.
• Data: Treat all incoming Intent extras as untrusted. Validate all schema/data types before consumption.

WebView

• JS: Default to javaScriptEnabled = false. Use WebViewClient and WebChromeClient to restrict navigation and origin access.
• File Access: Disable allowFileAccess and allowFileAccessFromFileURLs to prevent local file theft via XSS.
• Bridge: If creating a JavascriptInterface, use @JavascriptInterface (API 17+) and strictly limit the exposed API surface.

Storage & Files

• File Exposure: NEVER expose file:// URIs. Use FileProvider (androidx) to generate content:// URIs with temporary permissions.
• SharedPreferences: Use EncryptedSharedPreferences (Security library) for auth tokens and PII. Never use MODE_WORLD_READABLE (deprecated/insecure).
• Network: Use NetworkSecurityConfig to disable cleartextTrafficPermitted (mandatory for API 28+) and implement SSL Pinning/Certificate Pinning.

Anti-Patterns

• No Implicit Intents Internally: Use explicit intents with the component class name.
• No MODE_WORLD_READABLE: Never use for SharedPreferences or files.

References

• Hardening Examples