Android Banking Trojan 'Gustuff' Becomes More Dangerous

An Android banking Trojan that has been around since 2018 has evolved into one of the most serious of financial threats, according to a report by Group-IB.

They put the Trojan -- named Gustuff -- into the same threat tier as Anubis, Red Alert, Exobot, LokiBot and BankBot.

Inside of it are web fakes designed to target users of the Android apps used by top banks including Bank of America, Bank of Scotland, J.P.Morgan, Wells Fargo, Capital One, TD Bank and PNC Bank.

It also tries to take over crypto services such as Bitcoin Wallet, BitPay, Cryptopay and Coinbase. Payment services like PayPal, Revolut, Western Union, eBay, Walmart and WhatsApp can also be spoofed by the Trojan.

Group-IB specialists said that they discovered that Gustuff could potentially target users of more than 100 banking apps. These apps will include 27 in the US, 16 in Poland, ten in Australia, nine in Germany, and eight in India besides the 32 cryptocurrency apps that appear to be vulnerable to it.

The infection method is fairly prosaic. It sends an SMS message to the phone containing a link to malicious Android Package (APK) file. APK is the file format used by the Android operating system for distribution and installation of applications.

Once infected, the Trojan may spread through the device's contact list or server database.

Gustuff is able to display fake push notifications with legitimate icons of the apps which allows it to impersonate the legitimate app. But it has one unique feature to it that makes it even more miserable. ATS (Automatic Transfer Systems) is a legitimate Android feature that autofills fields in many legitimate mobile banking apps, cryptocurrency wallets as well as other apps to speed things up. ATS is found in the Trojan and it will scale up thefts.

Now, ATS is implemented using the Accessibility Service that is targeted at people with disabilities. This allows the Trojan to successfully bypass security measures against interactions with other apps' windows that would otherwise be in effect.

Group-IB says it can also turn off Google Protect about 70% of the time.

The security firm also notes that, "Although the Trojan was developed by a Russian-speaking cybercriminal, Gustuff operates exclusively on international markets. All new Android Trojans offered on underground forums, including Gustuff, are designed to be used mainly outside Russia, and target customers of international companies."

Sam Bakken, senior product marketing manager at OneSpan, found a trend evolving with Gustuff. He told Security Now that "What's interesting is more and more modular malware that will target not only mobile banking or not only payment services or not only cryptowallets, but all of them. This particular example even targeted messaging and retail apps. What developers need to remember is that if their app handles payments in any way, shape or form, that right there makes it imperative to raise the level of the security within their app. Criminals are increasingly targeting mobile apps as consumers increasingly use them to buy things and move money around."

Android as an OS has some major security issues. But Bakken makes a good point. It's up to app developers to assume they will at some point be attacked, and find ways to bake in protection against those attacks.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.