A new malware campaign that targets Android-using Australian banking customers has been discovered and, while the approach is not particularly sophisticated, elements of the malware have put security professionals around the world on guard.
The campaign, built around Gustuff malware, was discovered by Cisco Talos researchers and disclosed in a blog post authored by Vitor Ventura. The malware was offered as a botnet-for-rent on Exploit.in and has been shown to have the potential to hit banks and financial institutions around the world.
Talos researchers found the code to be obfuscated and packed, a combination that makes it very difficult to analyze with standard debuggers. They discovered that the code has multiple layers of protection against being run in a sandbox or on a device with antimalware in place. Once the code decides it's safe to execute, though, it becomes very active, very quickly.
The malware finds and exfiltrates a user's contact list and banking credentials, using one for spreading itself and the other for setting up criminal financial activity. So far, the malware is using SMS to spread rather slowly — slowly enough, in fact, for it to remain under the radar of many protective systems. Thus, while it's not spreading quickly at this point, it has a target list that would allow extensive replication and spread.
"Usually we would see this sort of malware spreading by email. The SMS is slower but sidesteps some standard defense," says Craig Williams, director, outreach, at Cisco Talos.
There are three other factors of special note with this campaign. First, it requires user intervention; the victim receives an SMS message containing a link that must be clicked on to begin the infection chain. The second is that the malware, once active, can intercept and respond to the SMS messages used in many two-factor authentication schemes.
The third special factor is fascinating to other security professionals. "One thing they did call out was the ability of this malware to re-establish its communications via text message," says John Todd, executive director of Quad9. "If it gets disconnected, an inbound text message will allow it to reconnect. It's an out-of-band control mechanism to re-establish broken command-and-control communications."
While this campaign is aimed at Australian institutions and customers, Williams says there's no barrier to its use against institutions around the world. The list of mobile financial apps monitored includes those from every major bank and many major financial institutions in the US and Europe.
Given the nature of the malware's activities, there are few unbeatable technology solutions. "Because it spreads via SMS, it will come down to user education," Williams says. "Unfortunately, you can't patch the user, so it's always going to be a struggle."
Todd offers some specific instructions. "If you get an SMS from me with a URL in it, don't click on it. Don't click on a link in a text message unless you've gotten a phone call telling you to expect it," he says. "Don't click on a link with an IP address in it. You'll always want some DNS in the process, something with a recognizable name in it."
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