Improper Verification of Intent by Broadcast Receiver
The Android application uses a Broadcast Receiver that receives an Intent but does not properly verify that the Intent came from an authorized source.
Certain types of Intents, identified by action string, can only be broadcast by the operating system itself, not by third-party applications. However, when an application registers to receive these implicit system intents, it is also registered to receive any explicit intents. While a malicious application cannot send an implicit system intent, it can send an explicit intent to the target application, which may assume that any received intent is a valid implicit system intent and not an explicit intent from another application. This may lead to unintended behavior.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
The following example demonstrates the weakness.
The ShutdownReceiver class will handle the intent:
Because the method does not confirm that the intent action is the expected system intent, any received intent will trigger the shutdown procedure, as shown here:
An attacker can use this behavior to cause a denial of service.
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