North Korean threat actor targets small and midsize businesses with H0lyGh0st ransomware

The group’s standard methodology is to encrypt all files on the target device and use the file extension .h0lyenc, send the victim a sample of the files as proof, and then demand payment in Bitcoin in exchange for restoring access to the files.
As part of their extortion tactics, they also threaten to publish victim data on social media or send the data to the victims’ customers if they refuse to pay.
This blog is intended to capture part of MSTIC’s analysis of DEV-0530 tactics, present the protections Microsoft has implemented in security products, and share insights on DEV-0530 and H0lyGh0st ransomware with the broader security community to protect mutual customers.

MSTIC assesses that DEV-0530 has connections with another North Korean-based group tracked as PLUTONIUM (aka DarkSeoul or Andariel).
While the use of H0lyGh0st ransomware in campaigns is unique to DEV-0530, MSTIC has observed communications between the two groups, as well as DEV-0530 using tools created exclusively by PLUTONIUM.

As with any observed nation-state actor activity, Microsoft directly notifies customers that have been targeted or compromised, providing them with the information they need to secure their accounts.
Microsoft uses DEV-#### designations as a temporary name given to an unknown, emerging, or a developing cluster of threat activity, allowing MSTIC to track it.

MSTIC identified four variants under these families – BTLC_C.exe, HolyRS.exe, HolyLock.exe, and BLTC.exe – and clustered them based on code similarity, C2 infrastructure including C2 URL patterns, and ransom note text.
BTLC_C.exe is written in C++ and is classified as SiennaPurple, while the rest are written in Go, and all variants are compiled into .exe to target Windows systems.
Microsoft Defender Antivirus, which is built into and ships with Windows 10 and 11, detects and blocks BTLC_C.exe as SiennaPurple and the rest as SiennaBlue, providing protection for Windows users against all known variants the H0lyGh0st malware.

SiennaPurple ransomware family: BTLC_C.exe
BLTC_C.exe is a portable ransomware developed by DEV-0530 and was first seen in June 2021.
This ransomware doesn’t have many features compared to all malware variants in the SiennaBlue family.
Prominently, if not launched as an administrative user, the BLTC_C.exe malware displays the following hardcoded error before exiting:

“This program only execute under admin privilege”.
The malware uses a simple obfuscation method for strings where 0x30 is subtracted from the hex value of each character, such that the string “aic^ef^bi^abc0” is decoded to 193[.]56[.]29[.]123.
The indicators of compromise (IOCs) decoded from the BLTC_C.exe ransomware are consistent with all malware variants in the SiennaBlue family, including the C2 infrastructure and the HTTP beacon URL structure access.php?order=AccessRequest&cmn.
The BTLC_C.exe sample analyzed by MSTIC has the following PDB path: M:ForOPattack(utils)attack toolsBackdoorpowershellbtlc_CReleasebtlc_C.pdb.

SiennaBlue ransomware family: HolyRS.exe, HolyLocker.exe, and BTLC.exe
Between October 2021 and May 2022, MSTIC observed a cluster of new DEV-0530 ransomware variants written in Go.
Analysts classified these variants as SiennaBlue.
While new Go functions were added to the different variants over time, all the ransomware in the SiennaBlue family share the same core Go functions.

A deeper look into the Go functions used in the SiennaBlue ransomware showed that over time, the core functionality expanded to include features like various encryption options, string obfuscation, public key management, and support for the internet and intranet.

MSTIC assesses DEV-0530 successfully compromised several targets in multiple countries using HolyRS.exe in November 2021.
A review of the victims showed they were primarily small-to-midsized businesses, including manufacturing organizations, banks, schools, and event and meeting planning companies.
The victimology indicates that these victims are most likely targets of opportunity.
MSTIC suspects that DEV-0530 might have exploited vulnerabilities such as CVE-2022-26352 (DotCMS remote code execution vulnerability) on public-facing web applications and content management systems to gain initial access into target networks.
The SiennaBlue malware variants were then dropped and executed.
To date, MSTIC has not observed DEV-0530 using any 0-day exploits in their attacks.

After successfully compromising a network, DEV-0530 exfiltrated a full copy of the victims’ files.
Next, the attackers encrypted the contents of the victim device, replacing all file names with Base64-encoded versions of the file names and renaming the extension to .h0lyenc.
Victims found a ransom note in C:FOR_DECRYPT.html, as well as an email from the attackers.

BTLC.exe is the latest DEV-0530 ransomware variant and has been seen in the wild since April 2022.
BTLC.exe can be configured to connect to a network share using the default username, password, and intranet URL hardcoded in the malware if the ServerBaseURL is not accessible from the device.
One notable feature added to BTLC.exe is a persistence mechanism in which the malware creates or deletes a scheduled task called lockertask, such that the following command line syntax can be used to launch the ransomware:

cmd.exe /Q /c schtasks /create /tn lockertask /tr [File] /sc minute /mo 1 /F /ru system 1> \127.0.0.1ADMIN$__[randomnumber] 2>&1
Once the ransomware is successfully launched as an administrator, it tries to connect to the default ServerBaseURL hardcoded in the malware, attempts to upload a public key to the C2 server, and encrypts all files in the victim’s drive.
ive.