New 'Quantum' Builder Lets Attackers Easily Create Malicious Windows Shortcuts

A new malware tool that enables cybercriminal actors to build malicious Windows shortcut (.LNK) files has been spotted for sale on cybercrime forums.

Dubbed Quantum Lnk Builder, the software makes it possible to spoof any extension and choose from over 300 icons, not to mention support UAC and Windows SmartScreen bypass as well as “multiple payloads per .LNK” file. Also offered are capabilities to generate .HTA and disk image (.ISO) payloads.

Quantum Builder is available for lease at different price points: €189 a month, €355 for two months, €899 for six months, or as a one-off lifetime purchase for €1,500.

“.LNK files are shortcut files that reference other files, folders, or applications to open them,” Cyble researchers said in a report. “The [threat actor] leverages the .LNK files and drops malicious payloads using LOLBins [living-off-the-land binaries].”

Early evidence of malware samples using Quantum Builder in the wild is said to date back to May 24, masquerading as harmless-looking text files (“test.txt.lnk”).

“By default, Windows hides the .LNK extension, so if a file is named as file_name.txt.lnk, then only file_name.txt will be visible to the user even if the show file extension option is enabled,” the researchers said. “For such reasons, this might be an attractive option for TAs, using the .LNK files as a disguise or smokescreen.”

Launching the .LNK file executes PowerShell code that, in turn, runs a HTML application (“bdg.hta”) file hosted on Quantum’s website (“quantum-software[.]online”) using MSHTA, a legitimate Windows utility that’s used to run HTA files.

Quantum Builder is said to share ties with the North Korean-based Lazarus Group based on source code-level overlaps in the tool and the latter’s modus operandi of leveraging .LNK files for delivering further stage payloads, indicating its potential use by APT actors in their attacks.

The development comes as operators behind Bumblebee and Emotet are shifting to .LNK files as a conduit to trigger the infection chains following Microsoft’s decision to disable Visual Basic for Applications (VBA) macros by default across its products earlier this year.

Bumblebee, a replacement for BazarLoader malware first spotted in March, functions as a backdoor designed to give the attackers persistent access to compromised systems and a downloader for other malware, including Cobalt Strike and Sliver.

The malware’s capabilities have also made it a tool of choice for threat actors, with 413 incidents of Bumblebee infection reported in May 2022, up from 41 in April, according to Cyble.

“Bumblebee is a new and highly sophisticated malware loader that employs extensive evasive maneuvers and anti-analysis tricks, including complex anti-virtualization techniques,” the researchers said. “It is likely to become a popular tool for ransomware groups to deliver their payload.”

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