Understanding the magnitude of the 3CXDesktopApp phenomenon


On March 29, 2023, CrowdStrike posted a blog sharing details about a supply chain attack involving a software called 3CXDesktopApp. On the same day, SentinelOne also shared details in relation to the same event. 3CXDesktopApp is a multi-platform application for desktops (Linux, MacOS, and Windows) that allows users to interact via chat, messaging, video, and voice.

The 3CXDesktopApp supply-chain attack started when a threat actor (which CrowdStrike identified to have links with the Lazarus Group) was able to embed arbitrary code into the official build of the software causing individuals and organizations fall victims of a global-scale campaign by downloading and running the 3CXDesktopApp installer from the developer’s website. Both Microsoft Windows and MacOS users were targeted as both the Windows and Mac versions were compromised.

On a Windows system, the MSI installer (3CXDesktopApp-18.12.416.msi, 3CXDesktopApp-18.12.407.msi) is designed to extract several files and to execute the file 3CXDesktopApp.exe which in turn loads a malicious library file named ffmpeg.dll (corresponding to the MD5 hashes 74bc2d0b6680faa1a5a76b27e5479cbc and 27b134af30f4a86f177db2f2555fe01d).


The DLL appeared to be originally compiled on Nov. 12, 2022, suggesting a long-term preparation of the attack. ffmpeg.dll was the first file on which I focused my attention. Within it I noted the function named dllmain_dispatch that appears as a custom implementation wrapping the standard DllMain function (basically called by the operating system when a DLL is loaded or unloaded). The function checks if the reason of the call is DLL_PROCESS_ATTACH or DLL_PROCESS_DETACH it calls the function sub_18004E250

sub_18004E250 is a wrapper of sub_18004DE60. The latter is basically designed to :

  1. create a new event named “AVMonitorRefreshEvent

2. search and load another malicious component named d3dcompiler_47.dll

3. Identify within it an encrypted payload having 0xC3FAEDFE as marker

4. Decrypt the payload-RC4-stream using the key 3jB(2bsG#@c7

5. Use the VirtualProtect() function to alter the memory access permissions

The decrypted payload appears to act as another loader that is designed to wait for certain amount of days before contacting a GitHub repository retrieving .ICO files having encrypted C&C strings within them.

The final payload appears to be a stealer able to extract and data from popular web browsers. This one, at time of writing, is not in my availability.


In the threat intelligence vertical, global telemetries are often used to assess the impact of a given campaign on a global scale; In this regard I have a certain degree of visibility (always considered partial and never complete) on the global diffusion of certain hashes as well as on the malicious network infrastructures they use. As already mentioned, the first files I focused on was the ffmpeg.dll one and the corrisponding hashes (74bc2d0b6680faa1a5a76b27e5479cbc and 27b134af30f4a86f177db2f2555fe01d). According to my visibility, the malicious toolset has been first observed on March 27, 2023 in Belgium, United States, Germany, Netherlands, Turkey and Israel impacting above all the Manifacturing, Industry, Finance, Hospitality and the Technology sectors (the latter at lower percentages). However, this data is to be considered not very indicative of the start of this campaign as the first detection signatures were massively released on that day. In fact researchers at Unit42 confirm the observation of SmoothOperator-linked artifacts as early as March 09, 2023. Map is derived by signature-based detections:

From my side, there is instead a very different situation if we instead consider telemetry based on malicious network infrastructures. SmoothOperator campaign leveraged on different domain names as Command and Control. They can be easily retrieved from the blog posts already reported above from CrowdStrike, SentinelOne and Unit42.

For example, if we considered the domain name msstorageazure[.]com, according to my visibility, it’s possibile to observe the first SmoothOperator-linked request to this domain starting on Feb. 10, 2023 (not necessarily indicating an active infection, but gives an idea of the time span of activity). Global resolution telemetries over this domain, up to March 29, 2023, confirms the Countries reported previously as potentially impacted, adding Spain, Canada, Portugal, Brazil, Austria, Switzerland, India, Thailand, Sweden and Australia.

The resolution telemetries (we are referring to devices that have communicated with malicious network infrastructures) for the domain akamaitechcloudservices[.]com add also Italy to the countries potentially impacted as on Feb. 17, 2023 resolution requests from this Country have been observed, referring at least to the Industrial and Manufacturing sectors.

According to the visibility I can dispose of, the final map of the proportions of this event is as follows:

Note that the maps refer to telemetry data which does not necessarily indicate an active infection in progress but an entity that has communicated with an infrastructure controlled by the threat actor. They are from before March 29, 2023.


3CXDesktopApp is a very used software and for this reason the SmoothOperator campaign received a lot of attention from the cyber security community. The potential damage caused by this supply-chain attack is very extensive and the effect of a compromise can be serious including the theft of data and sensitive information.


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