The infamous Carbanak group of hackers has been using multiple tools in a series of attacks over the past several months, Trustwave security researchers reveal.
Starting in September 2016, the Carbanak hackers began targeting large companies in the hospitality sector in Europe and the United States, in a series of attacks that are now said to have employed different types of malicious software.
In a recent report (PDF), Trustwave researchers revealed details on the malware used, some of the executables were signed with digital certificates issued by Comodo, in an attempt to bypass security controls. Most likely, the certs were acquired using fake identities, all featuring Russian details (city, address etc.).
The Carbanak group, also known as Anunak, was exposed in 2015 after supposedly stealing upwards of $1 billion from more than 100 banks across 30 countries.
Called Grand Mars, after one of the fake company names used to purchase certificates from Comodo, these latest attacks were not aiming at financial gains alone.
“The motivation of this operation appears to be financial gain, total control of the infrastructure and collection of bots within the victim organizations. During the forensics investigation and analysis, we were given the impression that several activities have been performed by different persons or even different groups of people,” Trustwave notes.
Multiple cybercrime organizations might have cooperated in the Grand Mars operation to establish a complex system of network hosts, using numerous malicious files to attack multiple victims. During the campaign, they switched command and control (C&C) servers to ensure they remain undetected, with majority of IP addresses associated with C&Cs located in Europe (UK, France, Sweden, and Germany), but some located in the United States.
Just as with other attacks performed by Carbanak, malicious macros in Microsoft Word documents attached to emails were used as entry points. As soon as the attachment was opened and the included VisualBasic script executed, four files were dropped onto the system, in an attempt to gain some foothold to it.
The dropped files include Starter.vbs, which uses registry Autorun and Task Scheduler to achieve persistence, TransbaseOdbcDriver.js, meant to connect to Google services (Forcepoint described the process earlier this week) and Pastebin for victim ID, tracking, and command retrieval, LanCradDriver.vbs, reads and executes the commands written in a LanCradDriver.ini file, initially created empty but later populated by the previous script, and dttsg.txt.
The attackers used a variety of tools to achieve persistence as well, namely a PowerShell Script (downloaded from Google Docs), Registry Autorun (they create a key in the registry to ensure the payload runs immediately after reboot), and Task Scheduler (a scheduled task is triggered every 30 minutes indefinitely to run starter.vbs and launch the execution chain: Starter.vbs> TransbaseOdbcDriver.js> LanCradDriver.vbs> LanCradDriver.ini).
Other tools used in this campaign and deemed malicious include AdobeUpdateManagementTool.vbs (designed to connect to C&C and perform data exfiltration), UVZHDVlZ.exe (a variant of the Carbanak malware), Update.exe (Cobalt Strike’s post-exploitation tool beacon), and 322.exe (a TCP reverse shell). These files were primarily designed for persistence or data exfiltration.
“Using services such as Google Docs in order to keep track of victims and spreading malicious files becomes a very big challenge for defenders because this way is very difficult to distinguish between good and bad guys using these popular public cloud services,” the report reads.
For lateral movement in the compromised networks, the attackers used pass-the-hash, which allowed them to steal credentials of a domain level, high privileged user, the security researchers reveal. Using this technique, actors steal credential hashes from a compromised system and can expand their foothold in the network if local accounts share the same password within the infrastructure.
“Ultimately this allowed attackers to achieve domain or even enterprise admin access and gain network access by utilizing several resources as Command & Control points in Europe and US. Further investigation of the attacked infrastructure showed that the intruders deployed similar PowerShell scripts or embedded batch files in order to spread within the environment,” Trustwave’s report reads.
While some of the attacks associated with this campaign might have been performed by various malicious groups (sometimes different stages of the same attack might have been performed by different groups, with others carrying later attack stages), “the attack characteristics of this family of malware share several common traits with the, original, well understood Carbanak APT campaign, which has been positively attributed to the Russian underground financial cybercrime network,” Trustwave concludes.