Adversaries don’t work 9-5 and neither do we. At eSentire, our 24/7 SOCs are staffed with Elite Threat Hunters and Cyber Analysts who hunt, investigate, contain and respond to threats within minutes.
We have discovered some of the most dangerous threats and nation state attacks in our space – including the Kaseya MSP breach and the more_eggs malware.
Our Security Operations Centers are supported with Threat Intelligence, Tactical Threat Response and Advanced Threat Analytics driven by our Threat Response Unit – the TRU team.
In TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We outline how we responded to the confirmed threat and what recommendations we have going forward.
Here’s the latest from our TRU Team…
What did we find?
In April 2024, eSentire’s Threat Response Unit (TRU) observed multiple incidents involving FIN7, a financially motivated threat group based in Russia that has been active since 2013. The threat actors used malicious websites to impersonate well-known brands, including AnyDesk, WinSCP, BlackRock, Asana, Concur, The Wall Street Journal, Workable, and Google Meet.
In this TRU Positive, we will look at incident cases with FIN7 delivering NetSupport RAT and DiceLoader for the subsequent stage in the infection chain.
Users visiting the malicious website via sponsored Google Ads would receive a fake pop-up prompting them to download a fake browser extension (Figure 1). The fake browser extension payload appears to be an MSIX file, a Windows app packaging format.
We found other websites controlled by FIN7 impersonating trusted brands using URLScan. You can find them here.
The MSIX files we have observed are signed with “SOFTWARE SP Z O O” and “SOFTWARE BYTES LTD”. We submitted the request to GlobalSign to get the certificates successfully revoked.
Infection Case One
Let’s look at the first case involving the infection with NetSupport RAT.
Upon extracting the MSIX file, we see that it contains the malicious PowerShell script (Figure 2).
The snippet of the malicious PowerShell script is shown below (Figure 3).
The PowerShell script collects system information such as the OS version and domain, retrieves the names of installed antivirus products, and generates a GUID. It then constructs a URL incorporating these details to download and Base64-decode a script from the C2 (Command and Control) server.
If the server response includes “usradm”, the script runs further commands to retrieve payloads from the C2 server. Additionally, the script manages exceptions during its execution and reports errors back to the C2 server via URL parameters (Figure 4).
The decoded script (Figure 5) downloads the NetSupport archive from the C2 server using a specific URL format: hxxps://cdn46[.]space/974afa0a-d334-48ec-a0d4-4cc14efa730c-1d3d044a-e654-41e3-ad32-38a2934393e4?aklshdjahsjdh=25&ajhsdjhasjhd=nsd&iud=$iudValue and user-agent “myUserAgentHere”.
Next, it extracts the contents of the zip file and stores the files under C:ProgramDatanetsupport path. Finally, the script executes the extracted NetSupport RAT executable.
Infection Case Two
The infection chain for the second case is like the first one, the user visited the malicious website meet-go[.]click to download a fake MSIX MeetGo installer. The MSIX payload dropped NetSupport RAT on the user’s machine. The threat actor connected to the machine approximately three hours later via NetSupport RAT.
The threat actors used curl to retrieve csvde.exe (MD5: b6f12d39edbfe3b33952be4329064b35) via hxxp://91.219.238[.]214:4673/01/csvde.exe, which is a command-line tool for Windows that allows the import and export of Active Directory data. The tool was used to execute the command:
- csvde.exe -r “(&(objectClass=Computer))” -l samAccountName,description,IPv4Address,info,operatingSystem -f 01cp.txt
The command exports data about computer objects into a text file (01cp.txt), including specific attributes like the account name, description, IP address, general info, and operating system details. Next, the threat actor used curl to retrieve “Adobe_017301.zip” (MD5: e7b1fb0ef5dd20f4522945b902803f10) zip archive via hxxp://91.219.238[.]214:4673/01/Adobe_017301.zip.
The contents (Figure 6) of the zip file are then extracted to c:programdata with the command:
- tar -zxvf c:programdataAdobe_017301.zip -C c:programdata
svchostc.exe is the renamed python.exe file (MD5: 0740803404a58d9c1c1f4bd9edaf4186) and svchostc.py (MD5: 782621d1062a8fc7d626ceb68af314e5) is the Python payload.
The threat actor then performed additional reconnaissance by running the command “whoami /upn”, which displays the user principal name (UPN) of the currently logged-in user.
The host’s persistence is achieved via scheduled tasks. The threat actor created the scheduled task “Updater” to run the Python payload “svchostc.py.”
- SCHTASKS /create /f /tn “MicrosoftWindowsUpdater” /tr “cmd /c c:programdataAdobe_017301svchostc.exe c:programdataAdobe_017301svchostc.py” /sc minute /mo 1 /RU “NT AUTHORITYSYSTEM”
The Python payload’s decryption and execution are implemented in the lambda function (_), which performs decryption operations such as string reversal and base64 decoding.
zlib decompression to retrieve the original executable content (Figure 7).
The decrypted output would contain the encrypted DiceLoader payload and the encrypted instructions to allocate memory with execute permissions, copy the decrypted payload into memory, and create and execute a new thread that runs the payload, effectively performing a process injection (Figure 8).
DiceLoader stores its C2 IPs and ports in the .data section. The data is XOR’ed with a hardcoded key located within the same section (Figure 10).
The incidents of FIN7 exploiting trusted brand names and using deceptive web ads to distribute NetSupport RAT followed by DiceLoader highlight the ongoing threat, particularly with the abuse of signed MSIX files by these actors, which has proven effective in their schemes.
What did we do?
Our team of 24/7 SOC Cyber Analysts isolated the affected hosts and notified the customer of suspicious activities.
What can you learn from this TRU Positive?
- Users should exercise caution when clicking on sponsored Google Ads, understanding that even legitimate-looking advertisement links can redirect to harmful content.
- The malicious websites impersonating reputable brands demonstrate the effectiveness of social engineering. Users should be cautious of downloading files from pop-up prompts, especially when browsing or redirected by ads.
- The deceptive use of signed MSIX files underscores the need for vigilance even with seemingly legitimate files. Users should verify file sources and be skeptical of any unexpected download prompts.
- The fact that the MSIX files were signed with company names but still contained malicious content highlights the importance of checking digital certificates and being aware that certification does not guarantee safety.
Recommendations from our Threat Response Unit (TRU):
We recommend implementing the following controls to help secure your organization against FIN7:
Indicators of Compromise
You can access the indicators here.
References
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