Recently, DeathRing, the latest pre-installed Android malware supposedly from China, was spotted in popular low-end smartphones sold in Asian and African countries including India, Vietnam, Indonesia, Nigeria, Taiwan and China.
This mobile Trojan disguises itself as a ringtone application and attempts to download other malware APKs, or target the user’s personal information and act as per the remote commands from a Command & Control server operated by cyber criminals. To avoid being uninstalled by the user, this malware is packed in the device as a system application.
One should now be paranoid about trusting a new smartphone. A precautionary action of scanning the new smartphone with a Mobile AV before use, or may be even before purchase, would stand as a temporary solution, but the Antivirus might not be able to remove the malware as it resides in the restricted-privilege system area.
Now, let us look briefly at what this malware does to achieve its malicious behavior. Even though this application is pre-loaded, supposing a user installs this application at will, the group permissions requested from the user during installation will be as shown in Figure 1 below.

Figure 1.Permissions requested from user during installation

Few of the important permissions to be granted by the user are shown in Figure 2 below. With these permissions, this Trojan app gains the ability to unmount and mount the phone’s file system with its desired privileges to install another malware APK in the system area, kill other running processes, interfere with a user’s outgoing calls and receive BOOT_COMPLETE information on device power-on.

Figure 2.Permissions list

Interestingly, this malware also requests permission to inject into user events (key, touch or trackball)  to deliver the event stream  to  the main activity of the Trojan.

Figure 3.Permission to inject into a user key event

Further analysis of this malware reveals that it also registers more than one callback and several services with the android system to start its malevolent behaviour with all possible intents that include ACTION_SHUTDOWN, NEW_OUTGOING_CALL etc., as shown in Figure 4.

Figure 4.Callbacks registered by the DeathRing malware

This malware carries the code to receive the key events in the main activity by declaring click listeners to trigger the corresponding relative activity.

Figure 5.Code to receive Click Listener

One of the relative activities listens for the key press events like onClick and onKeyDown from the SHUTDOWN key as a part of its malicious functionality as shown in Figure 6.

Figure 6.Code listening on shutdown button

This malware is also interested in the network state of the user’s device by first checking the user’s network type and subscriber ID, and then enabling the network connectivity based on the subscriber’s ID type.

Figure 7.Code identifying wi-fi connection

Figure 8.Code enabling network state

As proposed to Google in our last VB paper, an updated boot and broadcast framework that enabled the AV component to load earlier than any other application, even system applications, could help detecting and removing such malware.
Also, identifying and correcting the loophole through which the malware is loaded into the life-cycle of manufacturing and delivering the device at the earliest would help prevent pre-loaded malware, unless the presence of pre-loaded malware is not accidental.
K7 Mobile Security users are protected against this malware with the detection “Trojan (0001140e1)”.
V.Dhanalakshmi
Senior Threat Researcher, K7TCL
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