China-linked GIMMICK implant now targets macOS

Gimmick is a newly discovered macOS implant developed by the China-linked APT Storm Cloud and used to target organizations across Asia.

In late 2021, Volexity researchers investigated an intrusion in an environment they were monitoring and discovered a MacBook Pro running macOS 11.6 (Big Sur) that was compromised with a previously unknown macOS malware tracked as GIMMICK. The researchers explained that they have discovered Windows versions of the same implant during the past investigations.

The experts attribute the intrusion to a China-linked APT group tracked as Storm Cloud, which is known to target organizations across Asia.

The macOS version of the implant is written primarily in Objective C, while the Windows ones are in both .NET and Delphi. The implant uses public cloud hosting services (such as Google Drive) for C2 to evade detection.

Volexity worked with Apple to implement protections for the GIMMICK implant, on March 17, 2022, Apple pushed new signatures to XProtect and MRT to remove the malware.

GIMMICK should be launched directly by a user, rather than a daemon, then it installs itself as a launch agent by dropping a PLIST file with contents.

“On macOS, GIMMICK was found to support being launched as a daemon on the system or by a user. Should GIMMICK be launched directly by a user, rather than a daemon, it will install itself as a launch agent by dropping a PLIST file with contents, similar to that shown below, to /Users/<username>/Library/LaunchAgents.” reads the analysis published by Volexity. “The name of the binary, PLIST, and agent will vary per sample. In the case observed by Volexity, the implant was customized to imitate an application commonly launched by the targeted user.”

During the initialization, the implant analyzed by the experts decodes several pieces of data used by the implant for its operation using a rotating addition algorithm.

The implant also supports an uninstall function accessible by adding the argument “uninstall” on the command line. The command instructs the malicious code on removing itself and all associated files, and then kills the process.

“Storm Cloud is an advanced and versatile threat actor,  adapting its tool set to match different operating systems used by its targets.” concludes the analysis published by the experts. “The work involved in porting this malware and adapting its systems to a new operating system (macOS) is no light undertaking and suggests the threat actor behind it is well resourced, adept, and versatile.”

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Pierluigi Paganini

(SecurityAffairs – hacking, Gimmick)

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