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Blog — Apr 10, 2023

TRU Positives: Weekly investigation summaries and recommendations from eSentire's Threat Response Unit (TRU)

GuLoader Targeting the Financial Sector Using a Tax-themed Phishing Lure

5 minutes read
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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?

GuLoader, also known as CloudEyE, is a loader malware that is known to deliver additional malware, such as infostealers and Remote Access Trojans (RATs). The loader contains multiple stages of shellcode and is known for being one of the most advanced loaders with numerous anti-analysis techniques.

In March 2022, TRU observed GuLoader targeting the financial sector via the phishing email using a tax-themed lure. The phishing email contained a shared link to Adobe Acrobat, where the user could download the password-protected ZIP archive (Figure 1).

Figure 1: The malicious ZIP archive shared by an attacker

The ZIP archive contains a decoy image and a shortcut file disguised as a PDF (Figure 2).

Figure 2: Contents of the password-protected ZIP archive

The shortcut file leverages PowerShell to retrieve additional payloads from the website. Here is the example of the spawned PowerShell one-liner command:

Figure 3: The web server hosting Remcos RAT and GuLoader payloads

First, the command retrieves the VBS file from the encoded domain that translates to hxxp://109.206.240[.]67/xlog/Blotlg.vbs. The VBS file is saved under C:\Windows\Tasks and Remplice.vbs. Then the decoy PDF file is fetched and saved under the C:\Users\Public folder as details.pdf. The PDF file is then automatically opened to distract the user from the malicious VBS script execution in the background (Figure 4).

Figure 4: PDF decoy document

The obfuscated VBS script is responsible for writing the base64-encoded GuLoader shellcode payload to registry keys and executing the GuLoader payload via PowerShell (Figures 5-6).

The shellcode is written under:

Figure 5: The obfuscated VBS file
Figure 6: GuLoader shellcode payload written to the registry from the VBS file

GuLoader achieves persistence via Registry Run Keys (Figure 7). The registry data is a PowerShell command that retrieves the value of the 'Parlando' property for the registry key located at 'HKCU:\State'.

Figure 7: Persistence via Registry Run Keys

The “State” registry key contains the obfuscated PowerShell script that reflectively loads the GuLoader shellcode in memory (Figure 8).

Figure 8: Obfuscated PowerShell script

The secondary PowerShell script contains the strings that are XOR-ed with the decimal 50 (Figure 9). Upon decoding the script, we can observe that the PowerShell script is responsible for executing two shellcode buffers that are Base64-decoded and converted into a byte array.

Figure 9: Decoded PowerShell secondary script

The first 647 bytes of the shellcode are responsible for decoding the second part of the shellcode, which is the rest of the shellcode (Figure 10).

Figure 10: Decoding the shellcode

The shellcode retrieves the Remcos RAT from the web server (hxxp://109.206.240[.]67/xlog/TkhoWbbRT180.pfm) and injects it into the ieinstal.exe process.

Example of the data extracted from memory which is being sent to Remcos C2 from a sandbox environment:

||US|Windows 10 Enterprise (64 bit)|4294430720|4.4.0 Pro|C:\\ \AppData\Roaming\urtfghn.dat|C:\Program Files (x86)\internet explorer\ieinstal.exe|Filter|1|281|8314921|0|xlongactive[.]su|urtfghn-W5RHNP|0|C:\Program Files (x86)\internet explorer\ieinstal.exe|Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz|Exe|


How did we find it?

What did we do?

What can you learn from this TRU positive?

Recommendations from our Threat Response Unit (TRU) Team:

Indicators of Compromise







PowerShell obfuscated script




Decrypted shellcode


C2 (opendir)


Remcos RAT C2


Password-protected ZIP archive


eSentire’s Threat Response Unit (TRU) is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.

If you are not currently engaged with an MDR provider, eSentire MDR can help you reclaim the advantage and put your business ahead of disruption.

Learn what it means to have an elite team of Threat Hunters and Researchers that works for you. Connect with an eSentire Security Specialist.

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eSentire Threat Response Unit (TRU)
eSentire Threat Response Unit (TRU)

Our industry-renowned Threat Response Unit (TRU) is an elite team of threat hunters and researchers, that supports our 24/7 Security Operations Centers (SOCs), builds detection models across our Atlas XDR Cloud Platform, and works as an extension of your security team to continuously improve our Managed Detection and Response service. TRU has been recognized for its threat hunting, original research and content development capabilities. TRU is strategically organized into cross-functional groups to protect you against advanced and emerging threats, allowing your organization to gain leading threat intelligence and incredible cybersecurity acumen.