Security researchers from Palo Alto Networks have managed to identify distribution networks used by the Ursnif banking Trojan to target various users worldwide.
The Ursnif Trojan is distributed via spam emails that contain malicious attachments meant to download the Ursnif executable from a remote site. While analyzing the threat, Palo Alto researchers discovered that there are two main components in the malware’s distribution network, namely a spam botnet to send malicious emails, and compromised web servers to host the malware.
The spam botnet, researchers say, is focused on delivering either banking Trojans or malware downloaders to vulnerable machines in Japan, Italy, Spain, Poland, Australia, and Germany. The compromised web servers, on the other hand, host banking Trojans and spam bot files that malicious downloaders distributed by spam would drop onto compromised machines.
Throughout 2016, millions of spam messages, the majority written in Japanese, were sent to users in Japan, with Shiotob (a.k.a Bebloh or URLZone) being the most widely distributed threat (75 unique variants identified in 7 million spam emails). Although capable of stealing banking information itself, the malware was used only for downloading a secondary payload (such as Ursnif), at least in the second half of the year, the researchers say.
“Unit 42 observed millions of spam emails attacking Japanese recipients, some of whom could be running the banking Trojan and spam bot simultaneously. Though it is difficult to know the exact numbers of infections by the email campaign, we know the number is significant considering an increase in Japan-based IP addresses as a source of emails with malicious attachment,” Palo Alto says.
An analysis of 200 unique Japanese IP addresses that were spamming Shiotob revealed 250 unique malware samples being sent among 268,000 emails in 2016. While most payloads were either banking Trojans or downloaders, researchers discovered that attackers were adapting to the country. Thus, Ursnif and Shiotob were delivered in Australia; KINS and Ursnif in Italy; Shiotob and Ursnif in Japan; Ursnif and Tinba in Spain and Poland; and Ursnif and KINS in Germany.
Attackers were found to have made their infrastructure redundant by copying the malicious files on multiple servers. The researchers discovered more than 200 such files on 74 servers used by the threat actors between April 2015 and January 2017. Most were compromised personal or small-to-medium-sized business websites in Europe, which haven’t been maintained for years.
A breakdown of the malware found on these web servers revealed that Ursnif represented around half of the samples. KINS, Pushdo, Rovnix, Andromeda, Shiotob, and Zeus were also among the identified malware families.
“The actors deploying these banking Trojans use a spam bot network and compromised web servers. It is still unclear whether a single group attacks multiple countries with various threats by using the infrastructures, or if numerous threat actors share them,” the researchers note.