A rare chain of OpSec mistakes led to the discovery of a new Android banking botnet targeting Russian citizens that had been in operation since at least 2016. The Geost botnet, discovered by researchers from Czech Technical University, UNCUYO University, and Avast, infected over 800,000 Android devices (according to researchers’ estimation) and potentially controlled several million Euros. The researchers discovered a more startling story as they began to dissect the unencrypted chat logs found as part of their investigation.
The unusual discovery was made when the botmasters decided to trust a malicious proxy network built using a malware called HtBot. The HtBot malware provides a proxy service that can be rented to give users a pseudo-anonymous communication to the internet. Analysis of the HtBot network communication led to the discovery and disclosure of a large malicious operation infecting more than 800,000 Android-based devices.
In addition to a poor choice of anonymization platform to hide their tracks, the botmasters failed to encrypt their communications, allowing researchers an unprecedented view into their inner workings. The chat logs found revealed how they accessed servers, brought new devices into the botnet, and how they evade antivirus software, but it also contained something more intimate about the social relationships among the botmasters.
In one conversation, a member of the ring wants to leave the group but the leader encouraged him to stay, saying, “Alexander, really, if we started together we need to finish it. Because for now this is working and we can earn money. Not every day we are getting 100k for promotion.”
While it is not completely clear what is meant by “promotion,” the leader was also engaged in conversations about money laundering and payments using popular systems among Russian cybercriminals. Further analysis illustrated how the botmasters bring devices into the botnet, and how the delivery of the banking trojan and infiltration of the victim’s banking account follows.
“We really got an unprecedented view into how an operation like this functions,” said Anna Shirakova, researcher at Avast. “Because this group made some very poor choices in how it tried to hide its actions, we were able to see not just samples of the malware, but also delve deep into how the group works with lower level operatives bringing devices into the botnet and higher level operatives determining how much money was under their control. All told, there were over eight hundred thousand victims and the group potentially controlled millions in currency.”
Geost botnet and banking trojan
The Geost botnet seems to be a complex infrastructure of infected Android phones. The phones are infected with Android APKs that resemble different fake applications, such as fake banks and fake social networks. Once infected the phones connect to the botnet and are remotely controlled. The usual actions of the attackers seem to be accessing the SMS, sending SMS, communicating with banks, and redirect the traffic of the phone to different sites. The botmasters also access a great deal of personal information from the user.
Following the infection, the command and control stores the complete list of SMS messages of all the victims starting with the moment the device becomes infected. The SMSs were then processed offline in the C&C server to automatically compute the balance of each victim. On subsequent studies, it was possible for the researchers to understand the botmaster’s process for determining which online victims had the largest balance of money.
The botnet had a complex infrastructure including at least 13 C&C IP addresses, more than 140 domains, and more than 140 APK files. Five banks, mostly from Russia, were the primary targets of the banking trojan, and full details are revealed in the paper of the research.