July 18, 2024
Linux malware strengthens hyperlinks between Lazarus and the 3CX provide‑chain assault

Similarities with newly found Linux malware utilized in Operation DreamJob corroborate the idea that the notorious North Korea-aligned group is behind the 3CX supply-chain assault

ESET researchers have found a brand new Lazarus Operation DreamJob marketing campaign focusing on Linux customers. Operation DreamJob is the identify for a collection of campaigns the place the group makes use of social engineering methods to compromise its targets, with faux job gives because the lure. On this case, we had been capable of reconstruct the complete chain, from the ZIP file that delivers a faux HSBC job supply as a decoy, up till the ultimate payload: the SimplexTea Linux backdoor distributed by way of an OpenDrive cloud storage account. To our data, that is the primary public point out of this main North Korea-aligned menace actor utilizing Linux malware as a part of this operation.

Moreover, this discovery helped us verify with a excessive stage of confidence that the latest 3CX supply-chain assault was in reality performed by Lazarus – a hyperlink that was suspected from the very starting and demonstrated by a number of safety researchers since. On this blogpost, we corroborate these findings and supply extra proof concerning the connection between Lazarus and the 3CX supply-chain assault.

The 3CX supply-chain assault

3CX is a global VoIP software program developer and distributor that gives cellphone system providers to many organizations. In keeping with its web site, 3CX has greater than 600,000 prospects and 12,000,000 customers in varied sectors together with aerospace, healthcare, and hospitality. It gives shopper software program to make use of its methods through an online browser, cellular app, or a desktop software. Late in March 2023, it was found that the desktop software for each Home windows and macOS contained malicious code that enabled a bunch of attackers to obtain and run arbitrary code on all machines the place the appliance was put in. Quickly, it was decided that this malicious code was not one thing that 3CX added themselves, however that 3CX was compromised and that its software program was utilized in a supply-chain assault pushed by exterior menace actors to distribute extra malware to particular 3CX prospects.

This cyber-incident has made headlines in latest days. Initially reported on March 29th, 2023 in a Reddit thread by a CrowdStrike engineer, adopted by an official report by CrowdStrike, stating with excessive confidence that LABIRINTH CHOLLIMA, the corporate’s codename for Lazarus, was behind the assault (however omitting any proof backing up the declare). Due to the seriousness of the incident, a number of safety firms began to contribute their summaries of the occasions, particularly Sophos, Check Point, Broadcom, Trend Micro, and extra.

Additional, the a part of the assault affecting methods operating macOS was coated intimately in a Twitter thread and a blogpost by Patrick Wardle.

Timeline of occasions

Determine 1. Timeline of occasions associated to the preparation and distribution of 3CX trojanized purposes

The timeline reveals that the perpetrators had deliberate the assaults lengthy earlier than execution; as early as December 2022. This implies they already had a foothold inside 3CX’s community late final 12 months.

Whereas the trojanized 3CX macOS software reveals it was signed in late January, we didn’t see the dangerous software in our telemetry till February 14th, 2023. It’s unclear whether or not the malicious replace for macOS was distributed previous to that date.

Though ESET telemetry reveals the existence of the macOS second-stage payload as early as February, we didn’t have the pattern itself, nor metadata to tip us off about its maliciousness. We embody this info to assist defenders decide how far again methods may need been compromised.

A number of days earlier than the assault was publicly revealed, a mysterious Linux downloader was submitted to VirusTotal. It downloads a brand new Lazarus malicious payload for Linux and we clarify its relationship to the assault later within the textual content.

Attribution of the 3CX supply-chain assault to Lazarus

What’s already printed

There’s one area that performs a big function in our attribution reasoning: journalide[.]org. It’s talked about in among the vendor experiences linked above, however its presence is rarely defined. Curiously, articles by SentinelOne and ObjectiveSee don’t point out this area. Neither does a blogpost by Volexity, which even kept away from offering attribution, stating “Volexity can not at present map the disclosed exercise to any menace actor”. Its analysts had been among the many first to research the assault in depth they usually created a instrument to extract an inventory of C&C servers from encrypted icons on GitHub. This instrument is beneficial, because the attackers didn’t embed the C&C servers straight within the intermediate phases, however fairly used GitHub as a useless drop resolver. The intermediate phases are downloaders for Home windows and macOS that we denote as IconicLoaders, and the payloads they get as IconicStealer and UpdateAgent, respectively.

On March 30th, Joe Desimone, a safety researcher from Elastic Security, was among the many first to supply, in a Twitter thread, substantial clues that the 3CX-driven compromises are in all probability linked to Lazarus. He noticed {that a} shellcode stub prepended to the payload from d3dcompiler_47.dll is much like AppleJeus loader stubs attributed to Lazarus by CISA again in April 2021.

On March 31st it was being reported that 3CX had retained Mandiant to supply incident response providers referring to the supply-chain assault.

On April 3rd, Kaspersky, by way of its telemetry, confirmed a direct relationship between the 3CX supply-chain victims and the deployment of a backdoor dubbed Gopuram, each involving payloads with a typical identify, guard64.dll. Kaspersky knowledge reveals that Gopuram is linked to Lazarus as a result of it coexisted on sufferer machines alongside AppleJeus, malware that was already attributed to Lazarus. Each Gopuram and AppleJeus had been noticed in assaults in opposition to a cryptocurrency firm.

Then, on April 11th, the CISO of 3CX summarized Mandiant’s interim findings in a blogpost. In keeping with that report, two Home windows malware samples, a shellcode loader referred to as TAXHAUL and a fancy downloader named COLDCAT, had been concerned within the compromise of 3CX. No hashes had been offered, however Mandiant’s YARA rule, named TAXHAUL, additionally triggers on different samples already on VirusTotal:

  • SHA-1: 2ACC6F1D4656978F4D503929B8C804530D7E7CF6 (ualapi.dll),
  • SHA-1: DCEF83D8EE080B54DC54759C59F955E73D67AA65 (wlbsctrl.dll)

The filenames, however not MD5s, of those samples coincide with these from Kaspersky’s blogpost. Nonetheless, 3CX explicitly states that COLDCAT differs from Gopuram.

The subsequent part incorporates a technical description of the brand new Lazarus malicious Linux payload we not too long ago analyzed, in addition to the way it helped us strengthen the present hyperlink between Lazarus and the 3CX compromise.

Operation DreamJob with a Linux payload

The Lazarus group’s Operation DreamJob includes approaching targets by way of LinkedIn and tempting them with job gives from trade leaders. The identify was coined by ClearSky in a paper printed in August 2020. That paper describes a Lazarus cyberespionage marketing campaign focusing on protection and aerospace firms. The exercise has overlap with what we name Operation In(ter)ception, a collection of cyberespionage assaults which were ongoing since at the least September 2019. It targets aerospace, army, and protection firms and makes use of particular malicious, initially Home windows-only, instruments. Throughout July and August 2022, we discovered two situations of Operation In(ter)ception focusing on macOS. One malware pattern was submitted to VirusTotal from Brazil, and one other assault focused an ESET consumer in Argentina. A number of weeks in the past, a local Linux payload was discovered on VirusTotal with an HSBC-themed PDF lure. This completes Lazarus’s means to focus on all main desktop working methods.

On March 20th, a consumer within the nation of Georgia submitted to VirusTotal a ZIP archive referred to as HSBC job supply.pdf.zip. Given different DreamJob campaigns by Lazarus, this payload was in all probability distributed by way of spearphishing or direct messages on LinkedIn. The archive incorporates a single file: a local 64-bit Intel Linux binary written in Go and named HSBC job supply․pdf.

Curiously, the file extension just isn’t .pdf. It’s because the obvious dot character within the filename is a leader dot represented by the U+2024 Unicode character. The usage of the chief dot within the filename was in all probability an try and trick the file supervisor into treating the file as an executable as an alternative of a PDF. This might trigger the file to run when double-clicked as an alternative of opening it with a PDF viewer. On execution, a decoy PDF is exhibited to the consumer utilizing xdg-open, which is able to open the doc utilizing the consumer’s most popular PDF viewer (see Determine 3). We determined to name this ELF downloader OdicLoader, because it has the same function because the IconicLoaders on different platforms and the payload is fetched from OpenDrive.

OdicLoader drops a decoy PDF doc, shows it utilizing the system’s default PDF viewer (see Determine 2), after which downloads a second-stage backdoor from the OpenDrive cloud service. The downloaded file is saved in ~/.config/guiconfigd (SHA-1: 0CA1723AFE261CD85B05C9EF424FC50290DCE7DF). We name this second-stage backdoor SimplexTea.

Because the final step of its execution, the OdicLoader modifies ~/.bash_profile, so SimplexTea is launched with Bash and its output is muted (~/.config/guiconfigd >/dev/null 2>&1).

Determine 2. Illustration of the possible chain of compromise

Determine 3. An HSBC-themed lure within the Linux DreamJob marketing campaign

SimplexTea is a Linux backdoor written in C++. As highlighted in Desk 1, its class names are similar to operate names present in a pattern, with filename sysnetd, submitted to VirusTotal from Romania (SHA-1: F6760FB1F8B019AF2304EA6410001B63A1809F1D). Due to the similarities in school names and performance names between SimplexTea and sysnetd, we imagine SimplexTea is an up to date model, rewritten from C to C++.

Desk 1. Comparability of the unique image names from two Linux backdoors submitted to VirusTotal

(SimplexTea for Linux, from Georgia)

(BADCALL for Linux, from Romania)

CMsgCmd::Begin(void) MSG_Cmd
CMsgSafeDel::Begin(void) MSG_Del
CMsgDir::Begin(void) MSG_Dir
CMsgDown::Begin(void) MSG_Down
CMsgExit::Begin(void) MSG_Exit
CMsgReadConfig::Begin(void) MSG_ReadConfig
CMsgRun::Begin(void) MSG_Run
CMsgSetPath::Begin(void) MSG_SetPath
CMsgSleep::Begin(void) MSG_Sleep
CMsgTest::Begin(void) MSG_Test
CMsgUp::Begin(void) MSG_Up
CMsgWriteConfig::Begin(void) MSG_WriteConfig
CMsgZip::StartZip(void *)
CHttpWrapper::RecvData(uchar *&,uint *,uint,signed char)
CHttpWrapper::SendMsg(_MSG_STRUCT *) SendMsg
CHttpWrapper::SendData(uchar *,uint,uint)
CHttpWrapper::SendMsg(uint,uint,uchar *,uint,uint)
CHttpWrapper::SendLoginData(uchar *,uint,uchar *&,uint *)

How is sysnetd associated to Lazarus? The next part reveals similarities with Lazarus’s Home windows backdoor referred to as BADCALL.

BADCALL for Linux

We attribute sysnetd to Lazarus due to its similarities with the next two information (and we imagine that sysnetd is a Linux variant of the group’s backdoor for Home windows referred to as BADCALL):

  • P2P_DLL.dll (SHA-1: 65122E5129FC74D6B5EBAFCC3376ABAE0145BC14), which reveals code similarities to sysnetd within the type of domains used as a entrance for faux TLS connection (see Determine 4). It was attributed to Lazarus by CISA in December 2017. From September 2019, CISA began to name newer variations of this malware BADCALL (SHA-1: D288766FA268BC2534F85FD06A5D52264E646C47).

Determine 4. Similarities between a Home windows and a Linux variant of BADCALL (an inventory of domains used as a entrance for a faux TLS connection)

  • prtspool (SHA-1: 58B0516D28BD7218B1908FB266B8FE7582E22A5F), which reveals code similarities to sysnetd (see Determine 5). It was attributed to Lazarus by CISA in February 2021. Observe as effectively that SIMPLESEA, a macOS backdoor discovered through the 3CX incident response, implements the A5/1 stream cipher.

Determine 5. Similarities between AppleJeus for macOS and the Linux variant of BADCALL (the important thing for the A5/1 stream cipher)

This Linux model of the BADCALL backdoor, sysnetd, hundreds its configuration from a file named /tmp/vgauthsvclog. Since Lazarus operators have beforehand disguised their payloads, the usage of this identify, which is utilized by the VMware Visitor Authentication service, means that the focused system could also be a Linux VMware digital machine. Curiously, the XOR key on this case is similar as one utilized in SIMPLESEA from the 3CX investigation.

Determine 6. Loading a configuration file by BADCALL for Linux, cf. Determine 8

Looking on the three 32-bit integers, 0xC2B45678, 0x90ABCDEF, and 0xFE268455 from Determine 5, which signify a key for a customized implementation of the A5/1 cipher, we realized that the identical algorithm and the similar keys had been utilized in Home windows malware that dates again to the top of 2014 and was concerned in some of the infamous Lazarus instances: the cybersabotage of Sony Photos Leisure (SHA-1: 1C66E67A8531E3FF1C64AE57E6EDFDE7BEF2352D).

Determine 7. The decryption routine shared between the BADCALL for Linux and focused damaging malware for Home windows from 2014

Extra attribution knowledge factors

To recap what we’ve coated thus far, we attribute the 3CX supply-chain assault to the Lazarus group with a excessive stage of confidence. That is based mostly on the next components:

  1. Malware (the intrusion set):
    1. The IconicLoader (samcli.dll) makes use of the identical kind of robust encryption – AES-GCM – as SimplexTea (whose attribution to Lazarus was established through the similarity with BALLCALL for Linux); solely the keys and initialization vectors differ.
    2. Primarily based on the PE Wealthy Headers, each IconicLoader (samcli.dll) and IconicStealer (sechost.dll) are tasks of the same measurement and compiled in the identical Visible Studio atmosphere because the executables iertutil.dll (SHA-1: 5B03294B72C0CAA5FB20E7817002C600645EB475) and iertutil.dll (SHA-1: 7491BD61ED15298CE5EE5FFD01C8C82A2CDB40EC) reported within the Lazarus cryptocurrency campaigns by Volexity and Microsoft. We embody under the YARA rule RichHeaders_Lazarus_NukeSped_IconicPayloads_3CX_Q12023, which flags all these samples, and no unrelated malicious or clear information, as examined on the present ESET databases and up to date VirusTotal submissions.
    3. SimplexTea payload hundreds its configuration in a really comparable strategy to the SIMPLESEA malware from the 3CX official incident response. The XOR key differs (0x5E vs. 0x7E), however the configuration bears the identical identify: apdl.cf (see Determine 8).

Determine 8. Loading a configuration file by SimplexTea for Linux, cf. Determine 6

  1. Infrastructure:
    1. There’s shared community infrastructure with SimplexTea, because it makes use of https://journalide[.]org/djour.php because it C&C, whose area is reported within the official results of the incident response of the 3CX compromise by Mandiant.

Determine 9. A hardcoded URL in SimplexTea for Linux


The 3CX compromise has gained a number of consideration from the safety group since its disclosure on March 29th. This compromised software program, deployed on varied IT infrastructures, which permits the obtain and execution of any type of payload, can have devastating impacts. Sadly, no software program writer is resistant to being compromised and inadvertently distributing trojanized variations of their purposes.

The stealthiness of a supply-chain assault makes this technique of distributing malware very interesting from an attacker’s perspective. Lazarus has already used this system prior to now, focusing on South Korean customers of WIZVERA VeraPort software program in 2020. Similarities with current malware from the Lazarus toolset and with the group’s typical methods strongly recommend the latest 3CX compromise is the work of Lazarus as effectively.

It’s also attention-grabbing to notice that Lazarus can produce and use malware for all main desktop working methods: Home windows, macOS, and Linux. Each Home windows and macOS methods had been focused through the 3CX incident, with 3CX’s VoIP software program for each working methods being trojanized to incorporate malicious code to fetch arbitrary payloads. Within the case of 3CX, each Home windows and macOS second-stage malware variations exist. This text demonstrates the existence of a Linux backdoor that in all probability corresponds to the SIMPLESEA macOS malware seen within the 3CX incident. We named this Linux element SimplexTea and confirmed that it’s a part of Operation DreamJob, Lazarus’s flagship marketing campaign utilizing job gives to lure and compromise unsuspecting victims.

For any inquiries about our analysis printed on WeLiveSecurity, please contact us at [email protected].

ESET Analysis gives personal APT intelligence experiences and knowledge feeds. For any inquiries about this service, go to the ESET Threat Intelligence web page.



SHA-1 Filename ESET detection identify Description
0CA1723AFE261CD85B05C9EF424FC50290DCE7DF guiconfigd Linux/NukeSped.E SimplexTea for Linux.
3A63477A078CE10E53DFB5639E35D74F93CEFA81 HSBC_job_offer․pdf Linux/NukeSped.E OdicLoader, a 64-bit downloader for Linux, written in Go.
9D8BADE2030C93D0A010AA57B90915EB7D99EC82 HSBC_job_offer.pdf.zip Linux/NukeSped.E A ZIP archive with a Linux payload, from VirusTotal.
F6760FB1F8B019AF2304EA6410001B63A1809F1D sysnetd Linux/NukeSped.G BADCALL for Linux.


IP handle Area Internet hosting supplier First seen Particulars
23.254.211[.]230 N/A Hostwinds LLC. N/A C&C server for BADCALL for Linux
od[.]lk Cogent Communications 2023-03-16 Distant OpenDrive storage containing SimplexTea (/d/NTJfMzg4MDE1NzJf/vxmedia)
172.93.201[.]88 journalide[.]org Nexeon Applied sciences, Inc. 2023-03-29 C&C server for SimplexTea (/djour.php)

MITRE ATT&CK methods

Tactic ID Title Description
Reconnaissance T1593.001 Search Open Web sites/Domains: Social Media Lazarus attackers in all probability approached a goal with a faux HSBC-themed job supply that might match the goal’s curiosity. This has been finished principally through LinkedIn prior to now.
Useful resource Improvement T1584.001 Purchase Infrastructure: Domains Not like many earlier instances of compromised C&Cs utilized in Operation DreamJob, Lazarus operators registered their very own area for the Linux goal.
T1587.001 Develop Capabilities: Malware Customized instruments from the assault are very possible developed by the attackers.
T1585.003 Set up Accounts: Cloud Accounts The attackers hosted the ultimate stage on the cloud service OpenDrive.
T1608.001 Stage Capabilities: Add Malware The attackers hosted the ultimate stage on the cloud service OpenDrive.
Execution T1204.002 Consumer Execution: Malicious File OdicLoader masquerades as a PDF file with a view to idiot the goal.
Preliminary Entry T1566.002 Phishing: Spearphishing Hyperlink The goal possible acquired a hyperlink to third-party distant storage with a malicious ZIP archive, which was later submitted to VirusTotal.
Persistence T1546.004 Occasion Triggered Execution: Unix Shell Configuration Modification OdicLoader modifies the sufferer’s Bash profile, so SimplexTea is launched every time Bash is stared and its output is muted.
Protection Evasion T1134.002 Entry Token Manipulation: Create Course of with Token SimplexTea can create a brand new course of, if instructed by its C&C server.
T1140 Deobfuscate/Decode Recordsdata or Info SimplexTea shops its configuration in an encrypted apdl.cf.
T1027.009 Obfuscated Recordsdata or Info: Embedded Payloads The droppers of all malicious chains include an embedded knowledge array with a further stage.
T1562.003 Impair Defenses: Impair Command Historical past Logging OdicLoader modifies the sufferer’s Bash profile, so the output and error messages from SimplexTea are muted. SimplexTea executes new processes with the identical approach.
T1070.004 Indicator Elimination: File Deletion SimplexTea has the power to delete information securely.
T1497.003 Virtualization/Sandbox Evasion: Time Primarily based Evasion SimplexTea implements a number of customized sleep delays in its execution.
Discovery T1083 File and Listing Discovery SimplexTea can record the listing content material along with their names, sizes, and timestamps (mimicking the ls -la command).
Command and Management T1071.001 Software Layer Protocol: Internet Protocols SimplexTea can use HTTP and HTTPS for communication with its C&C server, utilizing a statically linked Curl library.
T1573.001 Encrypted Channel: Symmetric Cryptography SimplexTea encrypts C&C site visitors utilizing the AES-GCM algorithm.
T1132.001 Knowledge Encoding: Commonplace Encoding SimplexTea encodes C&C site visitors utilizing base64.
T1090 Proxy SimplexTea can make the most of a proxy for communications.
Exfiltration T1041 Exfiltration Over C2 Channel SimplexTea can exfiltrate knowledge as ZIP archives to its C&C server.


This YARA rule flags the cluster containing each IconicLoader and IconicStealer, in addition to the payloads deployed within the cryptocurrency campaigns from December 2022.