3CXDesktopApp Backdoored in a Suspected Lazarus Campaign  

Introduction

The attack involved a compromised version of the 3CX VoIP desktop client, which was used to target 3CX’s customers. The compromised 3CX application is a private automatic branch exchange (PABX) software and is available for Windows, macOS, Linux, Android, IOS and Chrome. Currently, there are reports of attacks for both Windows and macOS. 

The Qualys Threat Research Unit (TRU) is tracking a supply chain compromise in a popular VOIP desktop client by 3CX that is attributed to DPRK nation-state adversaries. The attack was reported in late March 2023 and is an ongoing investigation.  

Executive Summary

• The North Korean state-sponsored group Labyrinth Chollima have been identified as the perpetrators behind the supply chain compromise of 3CXDesktopApp beta 18.12.407 and final 18.12.416 applications. The affected applications are signed and have valid signatures.  
• The adversary infrastructure on GitHub used for staging the attack has now been taken down. This means that newer infections will not occur. However, the attack’s potential impact was significant, as the software is widely used by businesses around the world. 
• To mitigate the risk, affected users are recommended to immediately uninstall the application and perform a full system scan to detect and remove any associated malware.  
• This threat is being tracked as by MITRE as CVE-2023-29059 

Technical Summary 

Once the affected version of 3CX is installed or updated, it drops a compromised ffmpeg.dll as well as d3dcompiler_47.dll, which contains embedded shellcode. When 3CXDesktopApp starts, it sideloads the compromised ffmpeg.dll, which in turn decodes the embedded shellcode from d3dcompiler_47.dll and loads it. The shellcode accesses a GitHub repository and brings down icon files which contain encrypted C2 strings that the shellcode then decrypts and communicates to. The adversary has also deployed a previously unseen info stealer in the later stages of the attack and we have provided an analysis for it in later sections. This info stealer gathers system information and browser data from Chrome, Edge, Brave, and Firefox. This info stealer was likely meant to identify interesting targets for the operators. 

Existing customers of Qualys can follow the steps in the Detection and Protection sections to identify potential impacts. We also recommended that customers implement robust security measures, such as regular vulnerability assessments, patch management regular auditing of vendors. 

Overall, this supply chain attack highlights the importance of ensuring the security and integrity of the supply chain, as well as the need for businesses to remain vigilant and proactive in their security measures. 

Technical Analysis of Infection Stages 

First Stage Analysis 

The original MSI file which initiated the infection drops three files “3CXDesktopApp.exe”, “ffmpeg.dll”, and “d3dcompiler_47.dll”. 3CXDesktopApp.exe is the legitimate VOIP desktop application and is abused for side loading “ffmpeg.dll”.  

Once “ffmpeg.dll” is loaded, it tries to enumerate the current directory for the second DLL “d3dcompiler_47.dll”. Once found, the “ffmpeg.dll” loads the second DLL into memory. 

The “d3dcompiler_47.dll” DLL has an encrypted payload embedded in it. ffmpeg.dll tries to identify this payload using the signature “0xCEFAEDFE”. 

After the identification of the encrypted payload. “ffmpeg.dll” will try to decrypt it using the RC4 encryption scheme with the key “3jB(2bsG#@c7”. 

The decrypted payload is shown below. Also, a call to VirtualProtect() is made to give the PAGE_EXECUTE_READWRITE permissions for the payload to be executed. 

The decrypted payload that is going to be executed contains another embedded DLL as shown below. The DLL is dumped from memory to perform more investigations on it. 

Second Stage Analysis 

The embedded DLL will mainly try to fetch malicious “ico” files from the GitHub Repository “https://raw[.]githubusercontent[.]com/IconStorages/images/main/icon%d[.]ico”. The repository contains multiple icon files that have Base64 and AES encrypted C2’s appended to them. The full list of decoded C2’s is listed in the IOC section. This repository has already been taken down.  Qualys TRU detected an info stealer involved in the infection chain and considers it as a later-stage payload. 

Info Stealer Analysis 

The info stealer was deployed in the later stages of the infection chain and is a previously unseen sample. Its capabilities are mainly gathering system and browser information, including Chrome, Edge, Firefox, and Brave Browsers. 

The info stealer uses queries to fetch browsers history and data for Edge, SQLite database history for chrome and “Places” Table for Firefox. 

The info stealer also collects information on infected hosts, such as domain name, Hostname and OS Version, using NetWkstaGetInfo() API. Following locations are accessed by the information stealer: 

• Google Chrome – AppDataLocalGoogleChromeUser Data 
• Microsoft Edge – AppDataLocalMicrosoftEdgeUser Data 
• Brave Browser – AppDataLocalBraveSoftwareBrave-BrowserUser Data 
• Mozilla Firefox – AppDataRoamingMozillaFirefoxProfiles 

Qualys Detection & Protection 

The first step in assessing the risk of this attack to an organization is understanding if this software is in use. Users of the Qualys Cyber Security Asset Management can quickly identify all installed software across their organization. For example, within seconds, you can use the below query to identify assets with instances of the 3CX Desktop Application. 

software:(name:”3CX Desktop App 18.12″) 

Qualys VMDR also has QID 378327 ready to detect assets which have the vulnerable version of the 3CXDesktopApp.exe file present on their machines. Qualys Vulnerability Management Detection and Response (VMDR) users can scan their environment with this QID to quickly detect impacted systems. Example output: 

Alternatively, another option is to gather data from endpoints to hunt for the existence of the impacted software. Two such open-source scripts are available on GitHub. The 3cxIngectionHunter script will simply crawl the filesystem looking for instances of the infected ffmpeg.dll file and report back if there is a match to the malicious hash. The 3CXLocalDNSCacheHunter script will collect the local DNS cache and look for a match against some of the known URLs associated with this campaign. Using Qualys Custom Asset and Remediation, you can utilize the following PowerShell community scripts to identify potential infected assets by either copying the contents of the script manually or pointing the tool to the GitHub script directly to download.  

Users of Custom Assessment and Remediation and Qualys Patch Management can also push scripts to uninstall the impacted software automatically. These scripts will be published to GitHub in the coming days.  An example output from a system that does not have a vulnerable version of ffmpeg.dll installed: 

CAR can also be leveraged to remediate this vulnerability. You need to execute this uninstallation script provided by Qualys. This script checks for 3CX Desktop App’s vulnerable version 18.12.407.0 & 18.12.416.0 for Windows. If any of these versions are installed on the system, the script will attempt to uninstall the vulnerable application. 

You can also create dashboards for better visualization. 

Qualys Multi-Vector EDR customers are protected against this threat as both the installer and the beacon are detected and will be remediated. (Note: our instance was set to audit-only mode for analysis.) 

Multi-Vector EDR customers can also hunt through telemetry, looking for behavior indicators to identify this threat activity. A first step would look for instances where the 3cxdesktopapp.exe process executed in the environment using a QQL Query of process.name:”3xcdesktopapp.exe”. Here you would want to look for evidence of the ffmpeg.dll file being loaded, which would be indicative that this machine may be impacted by this campaign.  

While Qualys Endpoint Protection (EPP) users will be automatically protected by default, Qualys EDR-only customers can use the recently released auto-remediation feature to automatically take action.  

Conclusion 

Supply chain compromises are a growing concern for businesses, as they can lead to serious security breaches and financial losses. The attack was a multi-stage chain where attackers compromised a version of the 3CX VoIP desktop client, which was then used to target the company’s customers. This is reminiscent of the SolarWinds campaign that we examined back in December 2022. 

Organizations should take immediate steps to stop using the vulnerable version of the software, apply patches and monitor for anomalous behavior in 3CX processes. It is also essential to enable behavioral monitoring to detect the presence of such attacks within the system. 

MITRE TID Mapping

IOCS 

ffmpeg.dll 

C485674ee63ec8d4e8fde9800788175a8b02d3f9416d0e763360fff7f8eb4e02 

7986bbaee8940da11ce089383521ab420c443ab7b15ed42aed91fd31ce833896 

c485674ee63ec8d4e8fde9800788175a8b02d3f9416d0e763360fff7f8eb4e02 

d3dcompiler.dll 

11be1803e2e307b647a8a7e02d128335c448ff741bf06bf52b332e0bbf423b03 

11be1803e2e307b647a8a7e02d128335c448ff741bf06bf52b332e0bbf423b03 

Embedded dll 

F86A81B89C5FD4C98BC8616440FF0382505EC7942DA6D4F19EEE011E956434A8 

Trojanized 3cxDesktopApp 

Dde03348075512796241389dfea5560c20a3d2a2eac95c894e7bbed5e85a0acc 

Fad482ded2e25ce9e1dd3d3ecc3227af714bdfbbde04347dbc1b21d6a3670405 

92005051ae314d61074ed94a52e76b1c3e21e7f0e8c1d1fdd497a006ce45fa61 

B86c695822013483fa4e2dfdf712c5ee777d7b99cbad8c2fa2274b133481eadb 

Infostealer dll 

Cad1120d91b812acafef7175f949dd1b09c6c21a 

7faea2b01796b80d180399040bb69835 

GitHub Repository 

raw[.]githubusercontent[.]com/IconStorages/images/main/ 

C2s 

akamaicontainer[.]com 

akamaitechcloudservices[.]com 

azuredeploystore[.]com 

azureonlinecloud[.]com 

azureonlinestorage[.]com 

dunamistrd[.]com 

glcloudservice[.]com 

journalide[.]org 

msedgepackageinfo[.]com 

msstorageazure[.]com 

msstorageboxes[.]com 

officeaddons[.]com 

officestoragebox[.]com 

pbxcloudeservices[.]com 

pbxphonenetwork[.]com 

pbxsources[.]com 

qwepoi123098[.]com 

sbmsa[.]wiki 

sourceslabs[.]com 

visualstudiofactory[.]com 

zacharryblogs[.]com 

Icon File Hashes 

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Contributors

• Travis Smith, Vice President, Threat Research Unit, Qualys
• Irfan Asrar, Director, Malware and Threat Research, Qualys
• Mayuresh Dani, Manager, Threat Research. Qualys
• Sabri Naoufal, Senior Malware Analyst, Qualys
• Mohammad Shabbir, Malware Analyst, Qualys
• Akshat Pradhan, Senior Engineer, Threat Research, Qualys