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Don't Take the Bait: The XWorm Tax Scam

BY eSentire Threat Response Unit (TRU)

April 11, 2024 | 5 MINS READ

Threat Intelligence

Threat Response Unit

TRU Positive/Bulletin

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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?

Building on the insights from our previous exploration of finance-themed cybersecurity threats during the tax season, it's evident that digital dangers are vast and evolving.

This time, our 24/7 SOC Analysts notified our Threat Response Unit (TRU) about the tax-themed threat delivering XWorm as the final payload. We assess that it is almost certain the initial infection vector is via the phishing email, as suggested by the infection chain (Figure 1).

Figure 1: Infection chain.

We were able to track that the malicious attachment was downloaded from the compromised site hxxps://spnmandalawangi.banten.polri.go[.]id/Tax_docs_2023.htm. The downloaded file is a JavaScript file named “Tax-docs-2023.pdf .js” (MD5: 5706efd7e0254105261057a82308ed72).

When clicked by the victim, the JS file executes under Windows script host (wscript.exe) which retrieves and executes the atom.xml file (MD5: c1614e86b6808df891c5d7310d089211) from 91.92.243[.]28/poom/atom.xml (Figure 2).

Figure 2: Malicious command ran by the JavaScript file.

The retrieved file is a PowerShell script responsible for:

Figure 3: Snippet of the retrieved PowerShell script.
Figure 4: Decoy PDF file.
Figure 5: PowerShell script that adds the exclusions.
Figure 6: Disabling Windows Defender security features.
Figure 7: Persistence via Registry Run Keys

The ultimate payload delivered is XWorm v5.2, a Remote Access Trojan (RAT) (MD5: fc422800144383ef6e2e0eee37e7d6ba), for which cracked versions are publicly accessible.

Figure 8: XWorm payload in DnSpy

XWorm configuration:

C2: 91.92.243[.]28
Port: 4444
Aes key: <123456789>
Install file: USB.exe
Version: XWorm V5.2

What can you learn from this TRU Positive?

What did we do?

Our 24/7 SOC Cyber Analysts investigated the suspicious activities, notified the client, and isolated the affected device.

Recommendations from our Threat Response Unit (TRU) Team:

Detection Rules

You can access the Yara rule for XWorm here.

Indicators of Compromise

You can access the indicators of compromise here.


eSentire Unit
eSentire Threat Response Unit (TRU)

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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