D3F@ck Loader, the New MaaS Loader

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. 

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.

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

• LLC Kama Lubricant Company
• Ayog Tech Ltd
• Primalspeed Ltd

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).

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). 

All the strings are decoded as follows:

The loader creates a batch file named “performed.cmd” under %TEMP% folder; in our example, it’s under “C:UsersuserAppDataLocalTempis-8U6D1.tmp”.

The content of the batch script:

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 FilesWindows NT”. 

The batch script sets a variable named src to the path “C:Program FilesWindows NT” with set src=C:Program FilesWindows 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 FilesWindows 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:

• cmd /c attrib +s +h “str7” – this command attempts to hide the file “str7”, which is not present anywhere in the payload.
• cmd /c find /i “kernel” “C:Windowssystem32MRT.exe” – the command looks for the string “kernel” in MRT.exe binary which is a Windows Malicious Software Removal Tool, but the purpose of this command is still unknown. 

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.

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. 

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):

• hxxp://194.147.35[.]251/?v=3&event=ready&url=hxxp://116.202.188[.]155/auto/514170f7d05bc2fde4dfa2df54e33bca/125.exe”

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?

• The case of D3F@ck Loader illustrates how Malware-as-a-service (MaaS) continues to evolve, utilizing EV certificates to bypass trusted security measures.
  • This emphasizes the importance of staying updated on the latest threat tactics and ensuring that security solutions are robust enough to detect sophisticated attacks.
• Given that D3F@ck Loader spreads via Google Ads, it highlights the need for vigilance when clicking on advertisements, even on reputable platforms. Users should be cautious and verify the legitimacy of ads before engaging with their content.
• The loader’s ability to bypass major security features like Google Chrome’s and Microsoft’s SmartScreen underscores that while these tools are essential, they are not flawless. Users should not rely solely on automated security systems but should also adopt safe browsing practices and be skeptical of unfamiliar downloads.
• The fact that the final payload requires administrative privileges to run points out the critical role that privilege management plays in cybersecurity.
  • Users and administrators should practice the principle of least privilege, ensuring that accounts only have the permissions necessary for their functions to mitigate potential damage from malware.
• The impersonation of legitimate applications like Calendly and Rufus in the loader’s distribution strategy shows the continued use of social engineering by attackers. Educating users about these tactics can help prevent initial infection vectors from succeeding.

Recommendations from our Threat Response Unit (TRU):

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

• Confirm that all devices are protected with Endpoint Detection and Response (EDR) solutions.
• Implement a Phishing and Security Awareness Training (PSAT) Program that educates and informs your employees on emerging threats in the threat landscape.
• Encourage your employees to use password managers instead of using the password storage feature provided by web browsers. Use master passwords where applicable.
• Users and administrators must adhere to the principle of least privilege by limiting account permissions strictly to those necessary for their operational roles, helping to minimize potential damage from malware infections.

Indicators of Compromise

You can access the indicators here.

Source: Original Post