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The March 2023 3CX DesktopApp incident was a cascading software supply-chain attack: attackers first compromised an installer for Trading Technologies’ X_TRADER software, then used access gained through a 3CX employee’s computer to compromise 3CX’s build environments and distribute a trojanized desktop app. The affected-version lists and response instructions below are historical 2023 advisories, not a statement about which 3CX releases are safe today.
How did the 3CX supply-chain attack happen?
The incident involved two linked compromises. The initial compromise was a malware-laced X_TRADER installer downloaded from Trading Technologies’ website. The downstream compromise was the trojanized 3CX DesktopApp delivered to users.
Attackers entered through an X_TRADER installer
In its April 20, 2023 investigation, Mandiant said the intrusion into 3CX began in 2022 after an employee installed X_TRADER on a personal computer. The installer contained VEILEDSIGNAL malware. Mandiant reported that the installer was validly signed and remained available for download in 2022, although Trading Technologies had reportedly retired X_TRADER in 2020. 3CX’s April 20 update relayed those findings.
The intrusion reached 3CX’s build environments
Mandiant assessed that attackers stole corporate credentials from the employee’s compromised computer, entered the 3CX environment through a VPN, and used Fast Reverse Proxy for lateral movement. It reported that attackers compromised the Windows and macOS build environments used for the DesktopApp. Mandiant identified TAXHAUL and COLDCAT on the Windows build environment and POOLRAT on the macOS build server.
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The compromised builds carried a further payload
Mandiant’s analysis said affected DesktopApp releases included version 18.12.416 and earlier. It described malicious code launching the SUDDENICON downloader; encrypted icon files hosted on GitHub supplied command-and-control information, leading to an ICONICSTEALER stage that collected browser information. These are Mandiant’s technical findings about the attack chain.
What did researchers observe in the affected app?
CrowdStrike said it observed unexpected malicious activity on March 29, 2023, coming from a legitimate, signed 3CXDesktopApp binary. It reported beaconing to attacker-controlled infrastructure, delivery of second-stage payloads, and hands-on-keyboard activity in a small number of cases. CrowdStrike observed activity on both Windows and macOS.
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On March 30, 2023, CISA described the app as trojanized and warned that it could lead to multi-stage attacks against users of affected builds. CISA urged organizations to review technical reporting and hunt for indicators of compromise (IOCs). The advisories establish the attack and observed activity, but do not provide a reliable incident-wide count of affected organizations or confirmed compromises.
Who was behind the attack?
Attribution is an intelligence assessment, not a settled legal finding. Mandiant tracked the activity as UNC4736 and assessed with high confidence that the cluster had a North Korean nexus. CrowdStrike separately used the name LABYRINTH CHOLLIMA and described suspected nation-state involvement. Those labels and confidence statements belong to the respective researchers; they should not be treated as interchangeable proof of identity.
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Mandiant called the event the first time it had seen one software supply-chain attack lead to another. That statement describes Mandiant’s observed cases, not a definitive claim about every historical supply-chain attack.
Was my 3CX DesktopApp version affected?
The UK National Cyber Security Centre’s April 5, 2023 advisory listed these releases as affected. Its list is a dated historical reference, not a complete inventory of current software status.
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| Operating system | Versions listed by the UK NCSC in April 2023 | Update references in that advisory |
|---|---|---|
| Windows | 18.12.407 and 18.12.416 | Update 7 |
| macOS | 18.11.1213, 18.12.402, 18.12.407, and 18.12.416 | Updates 6 and 7 |
If you are checking a device now, do not use this 2023 list alone to decide whether an installed version is safe. Consult current 3CX security guidance and your organization’s security team for the release status and exposure assessment that apply today.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should organizations do if they had 3CX installed?
What the vendor advised in April 2023
In its April 1, 2023 update, 3CX recommended uninstalling the Electron DesktopApp from Windows and Mac computers, continuing antivirus and endpoint detection and response (EDR) scans with current signatures, and switching to the browser-based Progressive Web App (PWA). The vendor said its PWA required no installed binary and ran in the browser sandbox. These were the vendor’s instructions at that time, not current remediation guidance for every later incident.
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What government agencies advised at the time
CISA’s March 30, 2023 alert urged users and organizations to review technical reports and hunt for IOCs. The UK NCSC’s April 5 advisory directed organizations to consult the vendor alert and take its recommended actions. The Australian Cyber Security Centre also relayed the advice to remove the affected desktop client and use the browser-based Web App/PWA pending a secure release, while telling users to follow vendor updates.
The Australian agency said it had not received reports of Australian organizations being targeted at that time. That statement was limited to Australia and the date of its notice; it does not show that organizations elsewhere were unaffected.
If you are investigating possible exposure now
For a current or suspected incident, follow current vendor and organizational security-team instructions rather than treating the historical steps above as a complete response plan. Preserve the distinction between removing a client and investigating whether a device or network was compromised: CISA’s contemporaneous recommendation included IOC hunting, and an organization should route investigation and response through its security process.
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