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FIN7 Hackers Use LNK Embedded Objects in Fileless Attacks

The infamous FIN7 hacking group has been distributing malware through a LNK file embedded in a Word document via the Object Linking and Embedding (OLE) technology, Cisco Talos security researchers say.

The infamous FIN7 hacking group has been distributing malware through a LNK file embedded in a Word document via the Object Linking and Embedding (OLE) technology, Cisco Talos security researchers say.

FIN7, also known as Anunak, or Carbanak, is a financially motivated group that has been highly active since the beginning of this year. 

While analyzing the attack, the Talos researchers found that the hackers were using an RTF document containing an LNK embedded OLE object that extracted a JavaScript bot and injected an information stealer into memory using PowerShell. The tactic allowed the final payload to be executed onto the target machine without it ever touching the disk.

The use of RTF documents containing an embedded JavaScript OLE object isn’t a novel technique, and the use of LNK files for infection has been associated with the FIN7 group before. What the security researchers did discover, however, was that the JavaScript differs from one attack to another in order to avoid detection.

In early 2017, the group had been using multiple tools in attacks, and began refining their phishing techniques several months later, while also leveraging shims for persistence.

The use of reflective DLL injection PowerShell code in association with LNK embedded OLE objects for malware delivery shows that the sophisticated group is consistently changing techniques between attacks to avoid detection, Cisco Talos notes.

As part of the analyzed attack, the LNK file is used to execute wscript.exe with the beginning of the JavaScript chain from a Word document object. 

The DLL’s analysis reveals data stealing functionality and the targeting of a multitude of applications for this purpose, namely Outlook, Firefox, Google Chrome, Chromium, and forks of Chromium and Opera browsers.

The stolen data is dumped to %APPDATA%%USERNAME%.ini, then read and encrypted using the SimpleEncrypt function, after which it is sent to a hardcoded command and control (C&C) server using POST requests. The Google Apps Script hosting service is included among the hardcoded addresses, which is not surprising, as the Carbanak group was seen abusing Google services before.

“The FIN7 group is an example of an advanced adversary targeting a variety of industries using conventional technologies that ship with most versions of Microsoft Windows. Through the use of Microsoft Word documents to ship entire malware platforms they have the ability to leverage scripting languages to access ActiveX controls, and “file-less” techniques to inject shipped portable executables into memory using PowerShell without ever having the portable executable touch disk,” Cisco concludes.

Related: Carbanak Hackers Refine Intrusion Tactics

Related: FIN7 Hackers Change Phishing Techniques

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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