Moonstone Sleet (Storm-1789) – Threat Actor

Overview

Microsoft has identified a new North Korean threat actor, now tracked as Moonstone Sleet (formerly Storm-1789), which combines tried-and-true techniques used by other North Korean threat actors with unique attack methodologies to target companies for financial and cyberespionage objectives. Moonstone Sleet sets up fake companies and job opportunities to engage with potential targets, employs trojanized versions of legitimate tools, creates fully functional malicious games, and delivers custom ransomware.

The group uses tactics, techniques, and procedures (TTPs) that overlap with other North Korean threat actors, particularly Diamond Sleet, but has since shifted to its own infrastructure and attacks, establishing itself as a distinct, well-resourced North Korean threat actor. This highlights the evolving and collaborative nature of North Korean cyber threats, emphasizing the need for heightened security measures and vigilance.

Common targets

It targets individuals and organizations in the software and information technology, education, and defense industrial base sectors

Attack Vectors

Ransomware, phishing.

How they operate

North Korean hacking group Moonstone Sleet has been observed setting up fake companies and job opportunities to engage with potential targets. They employ trojanized versions of legitimate tools, create malicious games, and deliver new custom ransomware to their victims. This sophisticated strategy enables them to infiltrate systems and cause significant damage, highlighting the evolving threat landscape posed by state-sponsored cybercriminals. Enhanced vigilance and advanced security measures are crucial to combating such complex attacks.

Techniques Used 

Microsoft has observed Moonstone Sleet using the TTPs discussed in the following sections in various campaigns.

Trojanized PuTTY

In early August 2023, Microsoft observed Moonstone Sleet delivering a trojanized version of PuTTY, an open-source terminal emulator, via apps like LinkedIn and Telegram as well as developer freelancing platforms. Often, the actor sent targets a .zip archive containing two files: a trojanized version of putty.exe and url.txt, which contained an IP address and a password. If the provided IP and password were entered by the user into the PuTTY application, the application would decrypt an embedded payload, then load and execute it. The trojanized PuTTY executable drops a custom installer which kicks off execution of a series of stages of malware, as described below:

Stage 1 – Trojanized PuTTY: Decrypts, decompresses, and then executes the embedded stage 2 payload.

Stage 2 – SplitLoader installer/dropper: Decrypts, decompresses, and writes the Stage 3 payload, the SplitLoader DLL file, to disk. The installer also drops two encrypted files to disk, then executes SplitLoader via a scheduled task or registry run key.

Stage 3 – SplitLoader: Decrypts and decompresses the two encrypted files dropped by the stage 2 payload, then combines them to create the next-stage, another portable executable (PE) file.

Stage 4 – Trojan loader: Expects a compressed and encrypted PE file from the C2. Once received, the trojan loader decompresses, decrypts, and executes this file.

Malicious npm packages

Microsoft has observed Moonstone Sleet targeting potential victims with projects that used malicious npm packages. Often, the threat actor delivered these projects through freelancing websites or other platforms like LinkedIn. In one example, the threat actor used a fake company to send .zip files invoking a malicious npm package under the guise of a technical skills assessment. When loaded, the malicious package used curl to connect to an actor-controlled IP and drop additional malicious payloads like SplitLoader. In another incident, Moonstone Sleet delivered a malicious npm loader which led to credential theft from LSASS. Microsoft collaborated with GitHub to identify and remove repositories associated with this activity.

Malicious tank game

Since February 2024, Microsoft has observed Moonstone Sleet infecting devices using a malicious tank game it developed called DeTankWar (also called DeFiTankWar, DeTankZone, or TankWarsZone). DeTankWar is a fully functional downloadable game that requires player registration, including username/password and invite code. In this campaign, Moonstone Sleet typically approaches its targets through messaging platforms or by email, presenting itself as a game developer seeking investment or developer support and either masquerading as a legitimate blockchain company or using fake companies. To bolster the game’s superficial legitimacy, Moonstone Sleet has also created a robust public campaign that includes the websites detankwar[.]com and defitankzone[.]com, and many X (Twitter) accounts for the personas it uses to approach targets and for the game itself. Moonstone Sleet used a fake company called C.C. Waterfall to contact targets. The email presented the game as a blockchain-related project and offered the target the opportunity to collaborate, with a link to download the game included in the body of the message. When targeted users launch the game, delfi-tank-unity.exe, additional included malicious DLLs are also loaded. The payload is a custom malware loader that Microsoft tracks as YouieLoad. Similarly to SplitLoader, YouieLoad loads malicious payloads in memory and creates malicious services that perform functions such as network and user discovery and browser data collection. For compromised devices of particular interest to the group, the threat actor launches hands-on-keyboard commands with further discovery and conducts credential theft.

Ransomware

In April 2024, Microsoft observed Moonstone Sleet delivering a new custom ransomware variant we have named FakePenny against a company it previously compromised in February. FakePenny includes a loader and an encryptor. Although North Korean threat actor groups have previously developed custom ransomware, this is the first time we have observed this threat actor deploying ransomware. Microsoft assesses that Moonstone Sleet’s objective in deploying the ransomware is financial gain, suggesting the actor conducts cyber operations for both intelligence collection and revenue generation. Of note, the ransomware note dropped by FakePenny closely overlaps with the note used by Seashell Blizzard in its malware NotPetya. The ransom demand was $6.6M USD in BTC. This is in stark contrast to the lower ransom demands of previous North Korea ransomware attacks, like WannaCry 2.0 and H0lyGh0st.

Fake companies

Since January 2024, Microsoft has observed Moonstone Sleet creating several fake companies impersonating software development and IT services, typically relating to blockchain and AI. The actor has used these companies to reach out to potential targets, using a combination of created websites and social media accounts to add legitimacy to their campaigns.

StarGlow Ventures

From January to April 2024, Moonstone Sleet’s fake company StarGlow Ventures posed as a legitimate software development company. The group used a custom domain, fake employee personas, and social media accounts, in an email campaign targeting thousands of organizations in the education and software development sectors. In the emails Moonstone Sleet sent as part of this campaign, the actor complimented the work of the targeted organization and offered collaboration and support for upcoming projects, citing expertise in the development of web apps, mobile apps, blockchain, and AI. These emails also contained a 1×1 tracking pixel, which likely enabled Moonstone Sleet to track which targets engaged with the emails, and a link to a dummy unsubscribe page hosted on the StarGlow Ventures domain. While the emails did not contain any malicious links, Microsoft assesses Moonstone Sleet likely used this campaign to establish a relationship with target organizations. Although the purpose of these relationships is unclear, they may afford the actor access to organizations of interest or be used as revenue generation opportunities. Microsoft notified customers who were impacted by this Moonstone Sleet campaign.

C.C. Waterfall

In a similar campaign, Moonstone Sleet sent emails using its fake company C.C. Waterfall, a purported IT consulting organization. In this campaign, Moonstone Sleet emailed higher education organizations, claiming the company was either hiring new developers or looking for business collaboration opportunities. This campaign likely had similar goals to the StarGlow Ventures campaign: to build relationships with organizations which could be leveraged for revenue generation or malicious access. As previously mentioned, Moonstone Sleet also used C.C. Waterfall to contact targets and invite them to download the actor’s tank game, highlighting that this is a coordinated and concerted effort for which Moonstone Sleet can leverage multiple facets of its operations in overlapping campaigns.

Work-for-hire

In addition to creating fake companies, Microsoft has observed Moonstone Sleet pursuing employment in software development positions at multiple legitimate companies. This activity could be consistent with previous reporting from the United States Department of Justice that North Korea was using highly skilled remote IT workers to generate revenue. On the other hand, this Moonstone Sleet activity may also be another approach to gaining access to organizations.

Significant Attacks

• North Korean hacking group is targeting software companies and defense firms with custom ransomware variants and several elaborate scams. The new hacker group known as “Moonstone Sleet” uses several new tactics not previously seen among North Korean groups. (May 2024)

References:

• North Korea’s ‘Moonstone Sleet’ using fake tank game, custom ransomware in attacks
• Moonstone Sleet emerges as new North Korean threat actor with new bag of tricks