3CX Supply Chain Attack

THE THREAT

eSentire is aware of an ongoing supply chain attack impacting the voice and video conferencing application 3CXDesktopApp.

As of March 22nd, 2023, a digitally signed and trojanized version of the 3CX Voice Over Internet Protocol (VOIP) desktop client is being used in a supply chain attack to target 3CX customers. Attackers are targeting Windows and macOS users of the compromised 3CX softphone app.

The Electron Windows App version numbers 18.12.407 & 18.12.416, were compromised to include malicious content. Anti-Virus vendors have flagged the executable 3CXDesktopApp.exe and in some cases uninstalled it. Electron Mac App version numbers 18.11.1213, 18.12.402, 18.12.407, and 18.12.416 are also affected.

Malicious versions of the application result in the deployment of information stealer malware. This activity has been tentatively attributed to the North Korean state-sponsored Advanced Persistent Threat (APT) group Labyrinth Chomila. Organizations employing the malicious software are strongly recommended to uninstall the desktop application until a verified secure update is released.

What we’re doing about it

• eSentire has performed Threat Hunts for eSentire MDR for Endpoint and Log customers
  • Impacted organizations have been directly notified
• The eSentire Threat Intelligence team has detections and tracking in place for known Tactics, Techniques, and Procedures (TTPS) of the suspected nation-state threat actor, Labyrinth Chomila
• eSentire security teams are tracking this threat for additional details and detection opportunities where data is available.

What you should do about it

• 3CX recommends uninstalling the desktop application and migrating to the Progressive Web Application (PWA) deployment
• Reset user credentials on systems where the payloads were retrieved or could not be verified

Additional information

The supply chain attack, dubbed 'SmoothOperator,' starts when the MSI installer is downloaded from 3CX's website or when an update is pushed to an already installed desktop application.

When the MSI or update is installed, it will extract a malicious ffmpeg.dll and the d3dcompiler_47.dll DLL files, which are used to perform the next attack stage. The malware can harvest system info and steal data and stored credentials from Chrome, Edge, Brave, and Firefox user profiles.

Multiple customers have reported that the VoIP client app was marked malicious by Windows Defender, SentinelOne, CrowdStrike, ESET, Palo Alto Networks, and SonicWall security software. SentinelOne detects "penetration framework or shellcode" while analyzing the 3CXDesktopApp.exe binary, ESET tags it as a "Win64/Agent.CFM" trojan, Sophos as "Troj/Loader-AF," and CrowdStrike's Falcon OverWatch managed threat hunting service warns users to investigate their systems for malicious activity "urgently."

At this time, it remains unclear how the 3CX build was initially compromised. The eSentire Threat Intelligence team continues to track this topic for additional details and detection opportunities.

Impacted Application Versions:

• Electron Windows App - 18.12.407, 18.12.416
• Electron Mac App - 18.11.1213, 18.12.402, 18.12.407, 18.12.416

Domains contacted by the malicious application have been taken down. Publicly reported Indicators of Compromise (IoCs) are as follows:

References:

[1] https://www.sentinelone.com/blog/smoothoperator-ongoing-campaign-trojanizes-3cx-software-in-software-supply-chain-attack/
[2] https://news.sophos.com/en-us/2023/03/29/3cx-dll-sideloading-attack/
[3] https://www.crowdstrike.com/blog/crowdstrike-detects-and-prevents-active-intrusion-campaign-targeting-3cxdesktopapp-customers/
[4] https://www.huntress.com/blog/3cx-voip-software-compromise-supply-chain-threats
[5] https://www.microsoft.com/en-us/wdsi/threats/malware-encyclopedia-description?Name=Trojan:Win64/SamScissors
[6] https://www.3cx.com/community/threads/3cx-desktopapp-security-alert.119951/
[7] https://www.3cx.com/blog/news/desktopapp-security-alert/