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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?
Early in January 2024, our machine-learning-powered PowerShell classifier, BlueSteel, detected malicious PowerShell script execution. Upon further investigation the eSentire Threat Response Unit (TRU) associated the threat to SmartApeSG, a threat actor that relies on fake browser updates to distribute NetSupport RAT.
The execution was traced to the end-user visiting a compromised webpage which served a fake browser update ZIP containing Update_browser_17.6436.js. We could not retrieve the files or the compromised website, but we found similar samples here
and here.
The initial JavaScript file included legitimate code sections to conceal the malicious code (Figure 1).
Figure 1. Contents of the JS file
The code retrieves malicious script from jennifergalvin[.]com/cache/news.php?37668, as shown in Figure 2.
Figure 2: Deobfuscated JS content
The retrieved JavaScript file contains the PowerShell command shown in Figure 3.
Figure 3: Retrieved JS file containing the PowerShell command
The script does the following:
$bvQQOQYGOGdiqHsdLSvR is set to a URL (jesusanaya.com/GetData[.]php?10864).
$vxjoBVCFtQyMhM
downloads the content from the above URL.
$AcusblBKewkwXkdlGOMKgqQcFhnA converts the downloaded content from Base64 encoding.
A random number is generated, and a new directory path is created under the Application Data folder, appended with the random number.
The Base64 decoded data from the retrieved content is saved as a rtrs.zip file. The zip file is then extracted to the created directory.
The script checks for an executable client32.exe in the extracted directory. If found, it executes client32.exe.
A new registry item is created under the HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run path to ensure client32.exe runs on startup (T1547.001).
The Base64-encoded content mentioned above decodes to a ZIP archive (Figure 4). The archive contains NetSupport components, including the client (Figure 5).
Figure 4: Base64-encoded content that eventually decodes to a ZIP archiveFigure 5: NetSupport configuration file
Detection Rules
You can access the Yara rules for SmartApeSG here.
What did we do?
We investigated the threat and confirmed the activity is malicious.
SmartApeSG's use of fake browser updates to distribute the NetSupport RAT showcases a common social engineering technique, in which attackers often disguise malware as legitimate updates or software to trick users into downloading harmful files.
The compromised webpage serving a JavaScript file within a ZIP archive underlines the need for web security and caution when downloading files from websites, especially those that prompt unexpected updates or downloads.
The inclusion of legitimate code sections in the initial JavaScript file to hide malicious content is a classic obfuscation technique.
The PowerShell script's operations, including downloading content, creating directories, extracting ZIP files, executing executables, and modifying registry items, provide insights into typical NetSupport deployment strategies. This knowledge is crucial for developing robust detection and response mechanisms.
The decoding of Base64 content to reveal a ZIP archive containing NetSupport components highlights the multi-layered nature of malware deployment.
Recommendations from our Threat Response Unit (TRU) Team:
Identify file types that are commonly associated with security risks, such as executable files (.exe, .bat, .cmd), script files (.js, .vbs, .ps1), and certain document types that support macros (.docm, .xlsm). Then select a file type that is inherently safer and does not support executable code or active content (i.e., a plain text format like .txt).
Ensure employees have access to a dedicated software center to download corporate-approved software.
The eSentire Threat Response Unit (TRU) is an industry-leading threat research team committed to helping your organization become more resilient. TRU is an elite team of threat hunters and researchers that supports our 24/7 Security Operations Centers (SOCs), builds threat detection models across the eSentire XDR Cloud Platform, and works as an extension of your security team to continuously improve our Managed Detection and Response service. By providing complete visibility across your attack surface and performing global threat sweeps and proactive hypothesis-driven threat hunts augmented by original threat research, we are laser-focused on defending your organization against known and unknown threats.
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