The Carbanak Trojan was at the heart of the attacks. The banks were infected through spear phishing emails and the group took advantage of poorly patched, network-misconfigured systems.
Once a system was infected, the malware provided the conduit for FIN7 to covertly spy on staff, watch how they transferred cash, and then mimic the techniques to transfer funds fraudulently without detection.
Cybersecurity researchers from Seattle-based Icebrg have now uncovered a change in attitude from FIN7, which has ramped up its infiltration techniques to avoid detection.
In a blog post earlier this week, researchers Alex Sirr and Spencer Walden said that FIN7 has recently focused on improving their phishing documents, with the latest update receiving a concerning initial detections on VirusTotal of 0/59 and 1/59 for RTF and DOCX formats respectively -- which means that traditional antivirus software may not be enough to pick up malicious code embedded in a seemingly legitimate business email.
"While the newly observed malicious documents do not represent a "new" attack methodology, the change of payload may cause detection issues for legacy signatures and heuristic detections which utilize overly strict detection mechanisms, lacking in durability or layered coverage," the researchers said.
The threat actors use phishing to gain an initial foothold into a corporate network. Once complete, the group then paves their way through to Point of Sale (PoS) systems in order to steal credit card data, which can then be used in identity theft or potentially card cloning, should the information not be encrypted well.
FIN7 now uses a modified payload with an embedded file type for the first wave of attack. In the past, the cyberattackers have been spotted using malicious shortcut files (LNK) or visual basic scripts (VBS or VBE) to lay the trap for remote code execution.
These files were embedded into malicious documents using the Windows Object Linking and Embedding (OLE) framework.
However, it appears the hackers are now switching from LNK files to OLE embedded CMD files. These files are underlain with JScript, and writes a "tt.txt" files to the victim's home directory. The script then uses the JScript engine on the file, also leading to code execution, but is more difficult to spot.
In addition, FIN7's custom backdoor, HALFBAKED, has evolved. In the newest version, changes have been made to obfuscation techniques.
Originally, HALFBAKED utilized base64 encoding, stored in a string array variable called "srcTxt." Now, this name is obfuscated and the string is broken up into multiple strings.
The backdoor is also equipped with a command called "getNK2" which is designed to covertly pull a victim's full Microsoft Outlook email client auto-complete list, which suggests the threat group is keen to acquire as many new targets as possible.
"Detection authors must make trade-offs to optimize signature performance; narrow signatures lead to high fidelity detections, but risk missing changes in actor behaviors, meanwhile broader detection patterns provide better coverage, at the risk of more false positives," the researchers note. "Combatting a well-resourced and adaptive adversary requires a layered approach of both signature styles."
Must-have mobile apps to encrypt your texts and calls