Five malicious dropper Android apps with over 130,000 cumulative installations have been discovered on the Google Play Store distributing banking trojans like SharkBot and Vultur, which are capable of stealing financial data and performing on-device fraud.
"These droppers continue the unstopping evolution of malicious apps sneaking to the official store," Dutch mobile security firm ThreatFabric told The Hacker News in a statement.
"This evolution includes following newly introduced policies and masquerading as file managers and overcoming limitations by side-loading the malicious payload through the web browser."
Targets of these droppers include 231 banking and cryptocurrency wallet apps from financial institutions in Italy, the U.K., Germany, Spain, Poland, Austria, the U.S., Australia, France, and the Netherlands.
Dropper apps on official app stores like Google Play have increasingly become a popular and efficient technique to distribute banking malware to unsuspecting users, even as the threat actors behind those campaigns continually refine their tactics to bypass restrictions imposed by Google.
The list of malicious apps, four of which are still available on the digital marketplace, is below -
- Codice Fiscale 2022 (com.iatalytaxcode.app) - 10,000+ downloads
- File Manager Small, Lite (com.paskevicss752.usurf) - zero downloads
- My Finances Tracker (com.all.finance.plus) - 1,000+ downloads
- Recover Audio, Images & Videos (com.umac.recoverallfilepro) - 100,000+ downloads
- Zetter Authenticator (com.zetter.fastchecking) - 10,000+ downloads
The latest wave of SharkBot attacks aimed at Italian banking users since the start of October 2022 entailed the use of a dropper that masqueraded as an to determine the tax code in the country ("Codice Fiscale 2022").
While Google's Developer Program Policy limits the use of the REQUEST_INSTALL_PACKAGES permission to prevent it from being abused to install arbitrary app packages, the dropper, once launched, gets around this barrier by opening a fake Google Play store page impersonating the app listing, leading to the download of the malware under the guise of an update.
Outsourcing the malware retrieval to the browser is not the only method adopted by criminal actors. In another instance spotted by ThreatFabric, the dropper posed as a file manager app, which, per Google's revised policy, is a category that's allowed to have the REQUEST_INSTALL_PACKAGES permission.
Also spotted were three droppers that offered the advertised features but also came with a covert function that prompted the users to install an update upon opening the apps and grant them permission to install apps from unknown sources, leading to the delivery of Vultur.
The new variant of the trojan is notable for adding capabilities to extensively log user interface elements and interaction events (e.g., clicks, gestures, etc.), which ThreatFabric said could be a workaround to the use of the FLAG_SECURE window flag by banking apps to prevent them from being captured in screenshots.
The findings from ThreatFabric also come as Cyble uncovered an upgraded version of the Drinik Android trojan that targets 18 Indian banks by impersonating the country's official tax department app to siphon personal information through the abuse of the accessibility services API.
"Distribution through droppers on Google Play still remains the most 'affordable' and scalable way of reaching victims for most of the actors of different levels," the company noted.
"While sophisticated tactics like telephone-oriented attack delivery require more resources and are hard to scale, droppers on official and third-party stores allow threat actors to reach a wide unsuspecting audience with reasonable efforts."