FIN7 Hackers Using Weaponized Windows 11 Themed Word Document To Drop JavaScript Backdoor

Researchers uncovered a weaponized word document that mimics a malicious Windows 11 Alpha-theme used as a medium to drop a JavaScript payload with a JavaScript backdoor.

FIN7 is an APT threat group believed to reside in the Eastern European active since 2015, and this group considers as one of the notorious hacking groups targeted 100+ companies that involved with credit card theft of over 15 million payment card records that cost organizations around the world approximately one billion dollars (USD) in losses.

Researchers uncovered a weaponized word document that mimics a malicious Windows 11 Alpha-theme used as a medium to drop a JavaScript payload with a JavaScript backdoor.

FIN7 group operating with a different name including Carbon Spider, Gold Niagara, Calcium, also closely working with “Carbanak” another threat group that sharing TTP’s and their backdoor.

This group new come up with a new way of targeted attack by abusing the latest windows 11 update from Microsoft to inject a backdoor on the windows system using malicious Microsoft Word document (.doc) files.

Technical Analysis

The initial stage of the infection chain starts with an email phishing or spear-phishing campaign that contains a malicious Microsoft Word document (.doc) along with a decoy image posed as Windows 11 Alpha.

The image trick the victims to Enable Editing and Content to proceed to the next stage of the installation process, and the file embedded with the image contain a VBA macro. Once the victim enabled the content, then the Macro will be executed immediately.

Researchers from Anomali found a junk data is a common tactic used by threat actors to impede analysis. Once they remove this junk data, they are left with a VBA macro.

VBA Macro without Junk Data

Attackers also prevent the execution for some of the countries includes Russian, Ukrainian, Sorbian, Slovak, Slovenian, Estonian, Serbian, and if these languages are detected, the function me2XKr is called which deletes the table and stops running.

Also they are preventing the malware to execute on virtual machine and its stop the execution once its detected. Script also checks the following:-

  • Domain name, specifically CLEARMIND (Figure 9)
  • Language, if any of the languages listed in Table 1
  • Reg Key Language Preference for Russian
  • Virtual machine – VMWare, VirtualBox, innotek, QEMU, Oracle, Hyper and Parallels, if a VM is detected the script is killed (Figure 8)
  • Memory Available, if there is less than 4GB then don’t proceed
  • Check for RootDSE via LDAP

In-depth Analysis reveals an obfuscated strings, once replaced the obfuscated values with the deobfuscated strings, JavaScript backdoor functionalities are identified that are similar to the other FIN7 backdoors.

Finally, JavaScript backdoor is executed after connecting to the bypassociation[.]com address by checking the script for an active IP to retrieve the MAC address and DNSHostName.

“While not providing solid attribution, the language check function and table it scores against indicate a likely geographic location for the creator of this malicious doc file”. researchers said.

You can collect an IOC and malicious IP address here.

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