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ExpensiveWall: A dangerous ‘packed’ malware on Google Play that will hit your wallet

September 2017 by Check Point

Check Point’s mobile threat research team identified a new variant of an Android malware that sends fraudulent premium SMS messages and charges users’ accounts for fake services without their knowledge. According to Google Play data, the malware infected at least 50 apps and was downloaded between 1 million and 4.2 million times before the affected apps were removed.

The new strain of malware is dubbed “ExpensiveWall,” after one of the apps it uses to infect devices, “Lovely Wallpaper.” ExpensiveWall is a new variant of a malware found earlier this year on Google Play. The entire malware family has now been downloaded between 5.9 million and 21.1 million times.

What makes ExpensiveWall different than its other family members is that it is ‘packed’ – an advanced obfuscation technique used by malware developers to encrypt malicious code – allowing it to evade Google Play’s built-in anti-malware protections.

Check Point notified Google about ExpensiveWall on August 7, 2017, and Google promptly removed the reported samples from its store. However, even after the affected Apps were removed, within days another sample infiltrated Google Play, infecting more than 5,000 devices before it was removed four days later.

It’s important to point out that any infected app installed before it was removed from the App store, still remains installed on users’ devices. Users who downloaded these apps are therefore still at risk and should manually remove them from their devices.

What does ExpensiveWall do?

The malware registers victims to premium services without their knowledge and sends fraudulent premium SMS messages, charging their accounts for fake services.

Why is ExpensiveWall dangerous?

While ExpensiveWall is currently designed only to generate profit from its victims, a similar malware could be easily modified to use the same infrastructure in order to capture pictures, record audio, and even steal sensitive data and send the data to a command and control (C&C) server. Since the malware is capable of operating silently, all of this illicit activity takes place without the victim’s knowledge, turning it into the ultimate spying tool.

How does ExpensiveWall work?

Once ExpensiveWall is downloaded, it requests several common permissions, including internet access – which allows the app to connect to its C&C server – and SMS permissions – which enable it to send premium SMS messages and register users for other paid services all without the users knowledge.

While these permissions are harmful within the context of a malware, many apps request the same permissions for legitimate purposes. Most users grant these permissions without thinking, especially when installing an app from a trustworthy source such as Google Play.

ExpensiveWall contains an interface that connects between in-app actions and the JavaScript code, which runs on a web interface called WebView, meaning JavaScript running inside the WebView can trigger in-app activities. After it is installed and granted the necessary permissions, ExpensiveWall sends data about the infected device to its C&C server, including its location and unique identifiers, such as MAC and IP addresses, IMSI, and IMEI.




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