New macOS Backdoor Written in Rust Shows Possible Link with Windows Ransomware Group


February 08, 2024

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New macOS Backdoor Written in Rust Shows Possible Link with Windows Ransomware Group


Following our initial release, we have been contacted by our fellow researchers at Jamf who were able to identify three more samples that act like first-stage payloads. They are responsible for downloading the backdoor:

  • e7cab6f2be47940bf36e279bbec54ec7 -
  • 26d6a7e3507edf9953684d367dcd44bd -
  • 775851f86cbde630808ff6d2cf8cedbf -

Combined with information in our previous research, the investigation of these samples revealed new components of the attack, as well as several undocumented aspects related to C2 communication (hat tip to security researcher Vangelis tix Stykas for the valuable input on the C2 capabilities).

The newly discovered samples seem to predate the ones documented in our original research. They attempt to disguise as fake job offerings and have been initially released on Oct. 13, 2023.

Research on the command and control infrastructure has also shed some light on the main goal of the operation. Among the many victims we identified are several companies operating in the crypto-currency space. We are now in the process of notifying them about the attack.

The first two ZIP archives contain a basic shell script that is responsible for downloading and executing the backdoor component.

Along with the malware itself, the script also downloads a decoy PDF file holding a confidentiality agreement. The PDF file itself does not have any malicious purpose and serves as a decoy to distract users from the attack itself:

The third archive contains a downloader with the same functionality in the Contents/Resources/Scripts folder, but this time it consists of a compiled Apple Script, whose decompiled content is the following:

FAT binaries included in the application bundles

The last FAT binary has the identifier and is digitally signed by a developer ( X43S7HF655 ). Its purpose is to launch the main.scpt script using another compiled Apple script, CocoaAppletAppDelegate.scpt that is located in the Contents/Resources directory.

New Golang binaries used for environment discovery

After publishing the initial report, we identified 4 new Mach-O binaries that communicate with the domain, included in the list of IOCs. The new GO-based binaries are undetected on VirusTotal and have the following names: DataCollector (that encapsulates their core functionality), psaux and erp_soft

These samples have 2 user-defined functions, main.execCommand and main.sendDataToServer. Their purpose is to collect information about the victim’s machine and its network connections using the system_profiler and networksetup utilities, part of the macOS operating system.

Some of the executed commands are:

  • system_profiler SPSoftwareDataType SPHardwareDataType
  • networksetup -listallnetworkservices
  • networksetup -listallhardwareports

Also, they obtain the existing LaunchAgents/LaunchDaemons ( launchctl list ) command, extract details about the disk ( diskutil list ) and retrieve a wide list of kernel parameters and configuration values using the sysctl -a command.

GO binaries - IOCs

  • a91f92bb993fad6ccbd3fd4bb953f963
  • abdfe38311b621f54511b2afa434266e
  • 95a42a8c422c333c60467460479c66ba
  • 08ae923c3c6b7e94b61402ae8c0c396b

Revisiting the C2 communication

Further investigation on one of the C2 servers revealed additional endpoints available other than those initially documented. Queries to these endpoints expose both details about the victims and about the activity of the attackers. The most important endpoints found are:

  • GET /client/bots - See details about all installations of the backdoor. This endpoint leaks information about currently infected victims.
  • GET/tasks/result/<task_id> - Retrieve the result of any task, identified by its unique ID
  • POST /tasks/create -> Creates a new task
  • GET /redoc -> Display a short documentation of the endpoints in a web interface



Bitdefender researchers have discovered a new backdoor targeting macOS users. This previously undocumented family of malware is written in Rust and includes several interesting features. While the investigation is ongoing, we’re sending out this alert to share indicators of compromise with the community. Bitdefender products identify this threat as Trojan.MAC.RustDoor.*.

Here’s what we know so far:


The backdoor seems to impersonate a Visual Studio update, and all identified files are distributed directly as FAT binaries with Mach-O files for both x86_64 Intel and ARM architectures. None of the files have any other parents (Application Bundles, Disk images). Some of the identified samples are under the following names:

  • zshrc2
  • Previewers
  • VisualStudioUpdater
  • VisualStudioUpdater_Patch
  • VisualStudioUpdating
  • visualstudioupdate
  • DO_NOT_RUN_ChromeUpdates

We were able to trace the first samples back to early November 2023. The freshest sample was spotted on Feb 2nd 2024, indicating the malware has been operating undetected for at least three months.

Versions and capabilities

This backdoor seems to have multiple variants. While most of the samples share the same core functionalities (with minor variations), we split these samples into Variant 1, 2 and Zero, as documented below.

The files’ source code is written in Rust, and analysis of the binaries reveals the names of the original source files. Rust's syntax and semantics differ from those of  more common languages like C or Python, making it harder for security researchers to analyze and detect malicious code. This can give malware authors an advantage in evading detection and analysis.

A screenshot of a computer screen

Description automatically generated
Variant 1 source files

Variant 2 Source files
Variant 2 source files

All samples we analysed contain the backdoor functionality, with the following list of supported commands:

  • ps
  • shell
  • cd
  • mkdir
  • rm
  • rmdir
  • sleep
  • upload
  • botkill
  • dialog
  • taskkill
  • download

These commands allow the malware to gather and upload files, and gather information about the machine, as highlighted by the following arguments used in conjunction with the sysctl command:

  • machdep.cpu.vendor
  • machdep.cpu.brand_string
  • kern.osproductversion
  • hw.cpufrequency

The information extracted with the sysctl command, as well as the output of two other commands (pwd and hostname) are then submitted to the Register endpoint of the C&C server to receive a Victim ID. This Victim ID will be then used in the rest of communication between the C&C and backdoor.

Communication with the C2 servers is performed using the following endpoints:

  • POST /gateway/register: called when the file is executed and has the purpose of receiving an ID from the C2. The payload sent to the server contains 3 fields: hostname, os_version (the macOS version, ex: 13.6.4) and pwd (the current directory)
  • POST /gateway/report: called regularly at short timeintervals and the payload sent to the server containsonly one field, the idwith the value received as response from the /gateway/register call
  • /gateway/task: used to exchange information about the tasks executed on the compromised machine
  • /tasks/upload_file: used to exfiltrate files

At the moment of writing, the C2 servers are answering with {“detail”: “Not found”}

Variant 1

This variant, first seen on Nov 22, 2023, seems to be a testing version, as shown by the embedded plist file (which is copy-pasted from a public write-up describing persistence mechanisms and sandbox evasion techniques for macOS). Another possible clue is the name of the plist file (test.plist)

Although this embedded plist is meant to ensure persistence using LaunchAgents, the configuration does not include a field for this persistence method (only for persistence using cronjobs or inserting the application in the Dock bar), as seen in the second variant.

A computer screen shot of a blue screen

Description automatically generated

The variant 1 samples also contain an embedded JSON configuration, which is described in deeper detail in the Persistence section.

Variant 2

The files belonging to this second Variant were first seen on Nov. 30, 2023 and are slightly larger than their counterparts in version one, at around 4-5MB. This variant seems to be an upgraded version of the malware, that now contains a complex JSON configuration as well as an embedded Apple script used for exfiltration.

The embedded Apple script

  • We identified multiple variants of the embedded Apple script, but all of them are meant for data exfiltration
  • The script is used to exfiltrate documents with specific extensions and sizes from Documents and Desktop folders, as well as the notes of the user, stored in SQLITE format at the following location: /Users/<user>/Library/Group Containers/
  • Multiple strings containing the targeted extensions were also identified inside the binaries: txt, rtf, doc, xls, xlsx, png, pdf, pem, asc, ppk, rdp, zip, sql, ovpn, kdbx , conf, key, json
  • After all files are copied to the destination hidden folder, they are compressed into a ZIP archive (which has the name <username> and sent to the C2 server

The configuration options

The configuration options seem to include  a list of applications to be impersonated, with the purpose of spoofing the administrator password using a dialog, customized with different messages:

A blue screen with white text

Description automatically generated

Some configurations also include specific instructions about what data to collect, such as the maximum size and maximum number of files, as well as lists of targeted extensions and directories, or directories to  exclude:

A screen shot of a computer screen

Description automatically generated

The first part of the configuration suggests there are multiple ways to achieve persistence, as documented in the Persistence  section.

Variant Zero

Variant Zero seems to be the earliest one, and was first seen on 02.11.2023. Given the fact that it is presumably the original one, it is less complex than the other ones. While it has the backdoor functionality, the apple script and embedded configuration are absent.


As previously mentioned, the first two variants contain embedded JSON configurations that highlight multiple persistence mechanisms employed by this family, through fields like lock_in_cron, lock_in_launch, lock_in_dock or lock_in_rc. If the first two methods are quite common in recent malware families, the last two are not so popular.

  • lock_in_cron - Persistence using cronjobs
  • lock_in_launch - Persistence using LaunchAgents, causing the binary to be executed every time the user logs in. The path of the LaunchAgent is passed as parameter to the launchctl load –w <path_to_plist_file> command, which loads and starts the job, which will also restart on future logins.
A screen shot of a computer

Description automatically generated

.plist file created for persistence (

  • lock_in_rc - Persistence achieved by modifying the ~/.zshrc file, which is used to execute the binary every time a new ZSH session is opened.
  • lock_in_dock - Persistence achieved by adding the binary to the dock. This is done using the command defaults write persistent-apps -array-add. which modifies the file (located in ~/Library/Preferences folder). After modifying the file, the command killall Dock is executed to restart the Dock and apply the changes.

While the current information on Trojan.MAC.RustDoor is not enough to confidently attribute this campaign to a specific threat actor, artifacts and IoCs suggest a possible relationship with the BlackBasta and (ALPHV/BlackCat) ransomware operators.

Specifically, three out of the four command and control servers have been previously associated with ransomware campaigns targeting Windows clients. ALPHV/BlackCat is a ransomware family (also written in Rust), that first made its appearance in November 2021, and that has pioneered the public leaks business model.

Indicators of Compromise

Currently known indicators of compromise can be found below. Bitdefender Threat Intelligence customers can access enriched, contextual insights about this attack. The ThreatID BDapx7qeon in the Bitdefender IntelliZone portal includes additional TTPs and visualizations. For more information about Bitdefender Threat Intelligence solution visit our product page.


6dd3a3e4951d34446fe1a5c7cdf39754 (VisualStudioUpdater_Patch)

90a517c3dab8ceccf5f1a4c0f4932b1f (VisualStudioUpdater_Patch)

b67bba781e5cf006bd170a0850a9f2d0 (VisualStudioUpdating)

f5774aca722e0624daf67a2da5ec6967 (VisualStudioUpdater_Patch)

52a9d67745f153465fac434546007d3a (Previewers)

30b27b765878385161ca1ee71726a5c6 (DO_NOT_RUN_ChromeUpdates)

1dbc26447c1eaa9076e65285c92f7859 (visualstudioupdate)

05a8583f36599b5bc93fa3c349e89434 (VisualStudioUpdater)

5d0c62da036bbe375cb10659de1929e3 (VisualStudioUpdater)

68e0facbf541a2c014301346682ef9ca (VisualStudioUpdater)

b2bdd1d32983c35b3b1520d83d89d197 (zshrc2)

5fcc12eaba8185f9d0ddecafae8fd2d1 (zshrc2)






















Application bundles

  • e7cab6f2be47940bf36e279bbec54ec7 (
  • 26d6a7e3507edf9953684d367dcd44bd (
  • 775851f86cbde630808ff6d2cf8cedbf (

Download domains


Download scripts

  • 784d3a3a51ff811b4035ac72a9122ed3 - Trojan.MAC.Downloader.BK (Shell script)
  • 3fe70007c81f6938d872f0acdc7703ff - Trojan.MAC.Downloader.BJ (Compiled Apple script)
  • b74a98c673102db8f63e8139041728f5 - Trojan.MAC.Downloader.BL (Decompiled Apple script)





I'm a Security Researcher at Bitdefender, always trying to be one step ahead of cybercriminals targeting Unix. I am passionate about exploring the world and staying active through sports.

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