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Microsoft Workplace paperwork are used worldwide by each companies and residential customers. Its totally different workplace variations, whether or not licensed or unlicensed, provide customers a straightforward strategy to create and modify information. Nonetheless, this software program can be prone to cyberattacks.

Cyber ​​criminals usually reap the benefits of their vulnerability and use VBA (Visible Fundamental Utility) macros as entry factors to achieve entry to focus on methods and gadgets.

Over time, VBA macros have been a pervasive menace to Workplace paperwork with their capability to unfold malware. And that is why Microsoft lastly determined to dam VBA macros for information which have the ‘mark of the online’ (MOTW) tag. With this modification, every time customers open a file downloaded from the Web, resembling electronic mail attachments which have macros, the next message will probably be displayed:

Determine 1. Safety threat warning

Because of this, attackers at the moment are compelled to think about other ways to succeed in their victims. And that is the place Microsoft plugins come into the image.

What are Microsoft Add-ons?

An add-on is a software program program that extends the capabilities of the principle applications. It’s a time period generally utilized by Microsoft and different platforms which have further options that may be added to the principle applications. Workplace Add-ins are DLL information which have totally different extensions relying on the appliance. Microsoft Excel and Phrase have plugins with the file extensions, ‘.xll’ and ‘.wll’ respectively.

For the phrase, the ‘.wll’ The add-in should be positioned in a selected location, specified by the HKCUSoftwareMicrosoftOffice16.0WordSecurityTrusted Places registry worth, relying on the model of Workplace. This can be certain that ‘.wll’ the add-in runs via the Phrase utility.

For Excel add-ins, so long as ‘.xll’ the file is uploaded, it’ll open with an Excel utility.

Malicious XLL information

Many menace actors have began utilizing XLL information as their preliminary vector. These information are largely shared as an electronic mail attachment. It’s related to an icon much like one other Excel-compatible file, making it tough for finish customers to differentiate between the unique Excel file and an add-in file.

Determine 2. Malicious DLL with .XLL extension

When opening such information, Excel will show a warning in regards to the malicious code it incorporates.

Fig.3. MS Workplace Warning for Plugin

It’s doable for a “.dll” (dynamic hyperlink library) file to be renamed as a “.xll” (Excel Add-in) and is used for malicious functions. The distinction between a traditional DLL file and an XLL file is that XLLs can have sure exported capabilities that will probably be known as by the Excel Add-in supervisor if activated by the Excel utility. When Excel begins the XLL file, it’ll name the export capabilities based mostly on the XLL interface outlined as xlAutoOpen and xlAutoClose much like the strategies auto_open and automotive closed in VBA macros. These capabilities can be utilized to add malicious code and obtain the malware payload.

Technical evaluation:

It begins with a file known as “BankStatement-1674745402.xll”, which is a 64-bit DLL file. This file incorporates an export operate with the title “xlAutoOpen” as proven in determine 4.

Determine-4. DLL export operate

We now have run this DLL file explicitly utilizing “rundll32.exe” with the parameters,

“C:WindowsSysWOW64rundll32.exe C:UsersuserDesktop9009859256BankStatement-1674745402.xll, xlAutoOpen”.

In determine 5, we will see the execution move of the method.

Determine-5. Execution Course of Stream

The export operate has code (proven in Determine 6) that makes use of the strcat operate to generate totally different strings which have hyperlinks and instructions for execution. The next operate creates a hyperlink “http[:]//160[.]119[.]253[.]36/” and check out connecting to this hyperlink to obtain the zip file and put it aside as a “”.

Determine-6. Code for hyperlink technology and connection

After this, PowerShell is used to unzip this zip file to %Temp% folder with beneath talked about command,

“powershell.exe Develop-Archive –Path “” -DestinationPath “C:UsersuserAppDataLocalTemp””

After unzipping we get “configuration_file_v17.3.4” named folder within the %Temp% folder that has the “Sources” folder and “configuration_file_v17.3.4.jpg” file inside.

Determine-7. configuration_file_v17.3.4 folder in Temp

The sources folder has a number of XML information that comprise dummy knowledge. The attackers put that knowledge on function to make evaluation exhausting. He “configuration_file_v17.3.4.jpg” is just not a picture file format file. It’s nothing greater than a 32-bit PE file written in .NET language and appears like an installer for the Inno configuration module.

An Inno Setup is a well-liked free set up framework used to create installers for Home windows purposes. It supplies a scripting language that enables builders to customise the set up course of, together with creating shortcuts, registry entries, and different system settings.

Determine-8. configuration_file_v17.3.4.jpg file data in Die instrument

This .NET file has 213 strategies (proven in Determine 9) which might be closely obfuscated. We will de-obfuscate utilizing de4dot obfuscators To keep away from inverting a .NET utility, the creator has carried out a number of strategies to make it harder for any researcher to grasp the code and logic of the appliance.

Determine-9. “.NET Technique Depend”

This “configuration_file_v17.3.4.jpg” file executed utilizing beneath talked about command,

“cmd.exe /c begin C:UsersuserAppDataLocalTempfilesetup_v17.3.4filesetup_v17.3.4.jpg”

This file makes use of some anti-debugging methods at first of execution that are talked about beneath,

1. OllyDbg is a well-liked debugging instrument that can be utilized to research and modify working applications, together with .NET purposes. One approach to detect and stop debugging utilizing OllyDbg is to examine for the presence of a selected string related to the debugger.

Determine-10. OLLDBG Device Verify

2. Checking the debugger log, which is used to find out if a debugger is hooked up to the method and take applicable motion if one is discovered.

Determine-11. Debugger log examine

3. The IsDebuggerPresent operate is used to detect if a debugger is hooked up to the method or not.

4. The CheckRemoteDebuggerPresent operate is used to detect whether or not a debugger is linked to the present course of or a distant course of or not.

Determine-12. IsDebuggerPresent and CheckRemoteDebuggerPresent capabilities

Racoon Stealer V2 is a kind of malware designed to steal confidential data from contaminated methods. It’s able to stealing varied sorts of information together with .ttf and .xml information and storing them on the contaminated system. Nonetheless, if the CNC (command and management) server is down, the malware might not be capable of ship the stolen data to the server for exfiltration.

On this state of affairs, the stolen .ttf and .xml information can stay on the contaminated system till the CNC server turns into out there. This may doubtlessly expose delicate data to the attacker, since they will nonetheless entry the stolen information on the compromised system.

Quick Therapeutic Safety:

Fast Heal Safety Labs have been actively on the lookout for a lot of these information to make sure that all Fast Heal prospects are protected with the next detections.

  • Downldr.XllfmAgent.S29349494
  • Downldr.XllDanot.S29357788
  • Trojan.GenericRl.S24740760
  • Trojan.RacoonStealerCiR


In conclusion, Microsoft plugins can current a possible menace vector for malware like Raccoon Stealer V2. These kind of malware are designed to steal delicate data from contaminated methods and use Microsoft plug-ins as a method to ship the malware to focus on methods. To mitigate this threat, organizations ought to implement finest practices for endpoint safety, resembling retaining software program updated, implementing sturdy antivirus and antimalware options, enabling firewalls and different community safety measures, and educating customers. on steps to establish and keep away from social engineering assaults. By taking these steps, organizations can considerably scale back the chance of malware assaults and knowledge theft by way of Microsoft plug-ins and different potential assault vectors.





Malicious DLL file:









Malicious ZIP file:



Anjali Raut, Akshay Gaikwad