Android applications can receive broadcasts from the system or other applications. Receiving intents is security-sensitive. For example, it has led
in the past to the following vulnerabilities:
Receivers can be declared in the manifest or in the code to make them context-specific. If the receiver is declared in the manifest Android will
start the application if it is not already running once a matching broadcast is received. The receiver is an entry point into the application.
Other applications can send potentially malicious broadcasts, so it is important to consider broadcasts as untrusted and to limit the applications
that can send broadcasts to the receiver.
Permissions can be specified to restrict broadcasts to authorized applications. Restrictions can be enforced by both the sender and receiver of a
broadcast. If permissions are specified when registering a broadcast receiver, then only broadcasters who were granted this permission can send a
message to the receiver.
This rule raises an issue when a receiver is registered without specifying any broadcast permission.
Ask Yourself Whether
- The data extracted from intents is not sanitized.
- Intents broadcast is not restricted.
There is a risk if you answered yes to any of those questions.
Recommended Secure Coding Practices
Restrict the access to broadcasted intents. See the Android documentation for more
information.
Sensitive Code Example
<receiver android:name=".MyBroadcastReceiver" android:exported="true"> <!-- Sensitive -->
<intent-filter>
<action android:name="android.intent.action.AIRPLANE_MODE"/>
</intent-filter>
</receiver>
Compliant Solution
Enforce permissions:
<receiver android:name=".MyBroadcastReceiver"
android:permission="android.permission.SEND_SMS"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.AIRPLANE_MODE"/>
</intent-filter>
</receiver>
Do not export the receiver and only receive system intents:
<receiver android:name=".MyBroadcastReceiver" android:exported="false">
<intent-filter>
<action android:name="android.intent.action.AIRPLANE_MODE"/>
</intent-filter>
</receiver>
See
