CWE-926: Improper Export of Android Application Components

What is Improper Export of Android Application Components?

• Overview: Improper Export of Android Application Components (CWE-926) occurs when an Android application component is made available to other applications without proper access restrictions, allowing unauthorized access or interactions.

• Exploitation Methods:

• Attackers can exploit this vulnerability by launching exported activities, binding to unprotected services, or accessing data through content providers.
• Common attack patterns include invoking exported activities from malicious apps, interacting with services for unauthorized actions, and accessing sensitive data through improperly secured content providers.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive information, unauthorized actions within the application, and manipulations of the application's internal state.
• Potential cascading effects involve compromising user privacy, data leaks, and application instability.
• Business impact could involve loss of user trust, legal ramifications due to data breaches, and damage to the company's reputation.

• Prevention Guidelines:

• Specific code-level fixes include setting the android:exported attribute to false for components that should not be accessible outside the application and using permissions to restrict access.
• Security best practices involve conducting thorough security reviews of exported components and using intent filters with specified permissions.
• Recommended tools and frameworks include using security analysis tools like lint to detect improper exports and leveraging Android's built-in security features to enforce component access control.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Mobile

There are three types of components that can be exported in an Android application.

An Activity is an application component that provides a UI for users to interact with. A typical application will have multiple Activity screens that perform different functions, such as a main Activity screen and a separate settings Activity screen. A Service is an application component that is started by another component to execute an operation in the background, even after the invoking component is terminated. Services do not have a UI component visible to the user. The Content Provider mechanism can be used to share data with other applications or internally within the same application.

Vulnerable Code Example

Java Example

<application>
    <!-- Main activity is exported without restrictions -->
    <activity android:name=".MainActivity"
              android:exported="true">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

Explanation

In this vulnerable code example, the MainActivity is exported without any restrictions (android:exported="true"), which means any external application can launch this activity. This can lead to unauthorized access or manipulation of the application’s functions and data by other applications, posing a security risk.

How to fix Improper Export of Android Application Components?

To fix this vulnerability, it is crucial to restrict access to exported components by specifying permissions or setting android:exported to false when the component should not be accessible by other applications. If the component must be exported, use intent filters with specific actions and categories, and define proper permissions to control which applications can access the component.

Fixed Code Example

<application>
    <!-- Main activity is now secured with an intent filter and a custom permission -->
    <activity android:name=".MainActivity"
              android:exported="true"
              android:permission="com.example.myapp.permission.SECURE_LAUNCH">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
        <!-- Adding a custom intent filter to restrict access -->
        <intent-filter>
            <action android:name="com.example.myapp.SECURE_ACTION" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
</application>

Explanation

• Exported with Intent Filters and Permissions: The MainActivity is now protected by specifying a custom permission (com.example.myapp.permission.SECURE_LAUNCH) that controls which applications can launch this activity. This ensures that only applications with the declared permission can start this activity.
• Specific Intent Filters: Additional intent filters are used to define specific actions (com.example.myapp.SECURE_ACTION) that the activity can respond to, limiting exposure to only those operations that are intended to be public.

By applying these changes, the application components are protected from unauthorized access, reducing the risk of exploitation by malicious apps.