A harmless-looking currency converter application downloaded by more than 10,000 users from Google Play was designed to deliver the Cerberus banking Trojan.
A Malware-as-a-Service (Maas), Cerberus is known for its mobile remote access Trojan (mRAT) capabilities, as well as functionality through which it logs keystrokes and steals credentials, information from Google Authenticator, and SMS messages.
As part of the newly identified attack, the malware was disguised as a currency converter for Android users in Spain and managed to remain undetected by hiding the malicious activity for weeks after being submitted to Google Play.
Thus, it managed to rack up over 10,000 downloads before beginning the malicious routine of harvesting users’ banking data. Called Calculadora de Moneda, the application has already been reported to Google for removal, Avast’s security researchers reveal.
At a later stage, the application received updates that included dropper code, but the command and control (C&C) server only started issuing commands after a while longer, so as to avoid any suspicion from its users.
After months of benign operations, the application received a command from the C&C instructing it to download the Cerberus banking Trojan, which is designed to monitor users’ activity and display fake login pages over banking applications in use on the victim’s phone.
Thus, the Trojan steals a user’s login credentials and, due to its ability to read text messages and two-factor authentication details, might also be able to bypass security measures and compromise the banking account.
According to Avast, the C&C server was actively delivering the malicious payload for a short period of time, after which the server disappeared and “the currency converter app on Google Play no longer contained the Trojan malware,” a common tactic amongst cybercriminals looking to evade detection.
Users are advised to always make sure they use a verified banking app, to employ two-factor authentication, rely on trusted app stores only, check the ratings of new applications, and verify the permissions an application requires. Using a mobile security solution should help staying protected.
“Even though the malware slipped into Google Play, its payload was downloaded from an external source. If you deactivate the option to download apps from other sources, you will be safe from this type of banking Trojan activating on your phone,” Avast notes.