GM Bot: Alive and Upgraded, Now on Android M

IBM X-Force Research detected a recently updated version of the GM Bot mobile banking malware designed to deploy on Android 6 operating systems and bypass new security applied to the platform. Android officially released this Marshmallow OS, code-named M, in October 2015. The GM Bot version we analyzed can work on all Android versions up to the Marshmallow distribution.

This new finding is notable since GM Bot’s developer was banned in underground boards where he used to sell the malware. A competitor claimed that the original developer has stopped selling it. However, it’s now obvious that GM Bot is still alive and continuously updated to circumvent Android security. Attackers have been actively using the new version in the wild.

GM Bot Continues to Evolve

 Overlay Trojans, such as GM Bot and its derivatives, are designed to superimpose fraudulent message windows on top of banking and payment applications to phish credentials, credit card information and other personally identifiable information (PII). GM Bot’s spyware features also empower remote attackers to access transaction authorization codes sent via short message service (SMS), view device information, intercept, forward or initiate phone calls, or lock the device’s screen. Overlay malware is ultimately a cybercriminal’s way to gather victims’ online banking credentials and authentication factors all on one device.

In general terms, the overlay scheme works when the malware can:

• Identify which app was opened by the user and which app is running in the foreground.
• Launch a matching fake app screen on top of the running app.

The first task is often achieved by abusing Android getRunningTasks() application program interface (API). The option was deprecated starting with the Android Lollipop release, thus temporarily hampering the ability of overlay Trojans to figure out what the user is looking at.

Of course, cybercriminals operating Trojans of this type are not going to wait to find the next fix. Malware developers tried a variety of tricks to get past the new deprecation block, including:

• Getting the current foreground application via getRunningAppProcesses(), which was introduced and worked on Android 5.0 and 5.1 (Android L);
• Abusing the accessibility service to find out what’s running on the screen; and...
• In some cases, abusing the UsageStatsManager API.

GM Bot’s developer, known as GanjaMan, also found a way to bypass the deprecation block and implemented it in the most recent version of the malware. In this case, the developer did not go far into programming genius. Rather, he used an open-source method documented on GitHub and began implementing a process enumeration to find out which app was running in the foreground — a good, heuristic way to figure it out.

This post was part of my work with IBM X-Force. Read the complete post here.