Editor’s note: The current article is authored by the guest author WatchingRac, who is a threat intelligence analyst. You can find him on X.

This article covers two distinct methods used to infect systems with AsyncRAT via open directories. These techniques show how attackers are constantly adapting, finding new ways to use publicly accessible files to broaden AsyncRAT’s impact and reach.

Overview

AsyncRAT is a type of Remote Access Trojan (RAT) malware designed to stealthily infiltrate systems and give attackers remote control over infected devices. It is commonly used for spying, data theft, and manipulation of compromised systems.

Recently, two open directories surfaced, each employing unique methods to distribute and infect victims with AsyncRAT. These techniques highlight the persistent threat posed by this malware and its diverse infection strategies.

First Technique

Open Directory

While investigating malicious open directories exposed to the internet, I discovered one with an unusual structure.

The directory contained the following files:

A text file with an extensive string that turned out to be a VBS script

A JPG file that was actually a disguised ZIP archive

Analysis of the Txt file

The text file’s extensive string conceals an obfuscated VBS script. It uses random variables to store parts of the text that will be used to download the JPG file.

To make it easier to read we just need to make a few changes:

Replace the variables with the actual text

Use intuitive names for variables that are used to write or download files

Now we see that the VBS script creates an XML file OMjRRRRRRRRRRRRRRRRRRRRvbK.xml located at C:\Users\Public. The content of the XML file contains a PowerShell script that downloads the disguised JPG file, saves it, and extracts it to the same directory.

Once extracted, the process continues by executing another script, TesKKKeLAvaYdAfbBS.vbs. Then, it cleans up by deleting both the XML and ZIP files.

Analysis of the VBS file

The VBS script is also obfuscated and uses the same technique as the other text file. By examining the file, we can understand a few parts of its execution:

*Figure 4: TesKKKeLAvaYdAfbBS.vbs obfuscated*

To make it simple to read, we just need to make a few changes:

Replace the variables with the actual text

Use intuitive names for variables that are in use

Delete all the If statements that execute the same code regardless of the result

By making these changes, we can transform a 34-line VBS script into a simpler 6-line version that is easier to read.

*Figure 5: Clean TesKKKeLAvaYdAfbBS.vbs*

The VBS script will then execute the KKKKKKllLavIOOOOOtesAA.bat, which is the next stage.

Analysis of the Bat file

The BAT script is also obfuscated, but it is possible to understand its purpose by reading the values stored inside the variables vertically.

*Figure 6: KKKKKKllLavIOOOOOtesAA.bat file*

Its role is to execute PowerShell without a prompt window. It initiates the next stage by running KiLOvBeRNdautESaatnENn.ps1

Analysis of the PowerShell (PS1) file

The PS1 file is a simple script that creates a scheduled task named ‘tMicNet Work40,’ which runs UhLQoyDAMaCUTPaE.vbs every 2 minutes.

*Figure 7: Scheduled task created by PowerShell*

Analysis of the Second VBS file

UhLQoyDAMaCUTPaE.vbs has the same structure as the previous VBS (TesKKKeLAvaYdAfbBS.vbs), so we can use the same technique to make the script easier to read and analyze.

*Figure 8: UhLQoyDAMaCUTPaE.vbs obfuscated*

Using the same technique we will get this result:

*Figure 9: UhLQoyDAMaCUTPaE.vbs deobfuscated*

Analysis of The Second BAT file

aaaNOOTKiiiLAViiiiOOs.bat has the same structure as the previous BAT (KKKKKKllLavIOOOOOtesAA.bat), so by reading it vertically, we can figure out what the file does.

The BAT file executes the last stage, which is a Powershell file.

Analysis of the Last Stage

The final stage is obfuscated by changing the variable names to make the code harder to interpret. Instead of giving a straightforward name to the variable, they break the word into pieces, mix them up, and then call each position to reconstruct the variable name.

To simplify the analysis, we can deconstruct the code in a similar way, isolating each piece to make the script clearer and easier to understand.

The first part of the code is a function that receives a string and converts it from hexadecimal to a 32-bit integer.

*Figure 12: First part of the final stage*

The second part of the code contains two variables with large strings. Both strings use a replace function to retrieve the correct value, which are then sent to the ‘PARSer’ for further processing.

*Figure 13: Second part of the last stage*

The last part of the final stage is simply loading the files into memory to execute them.

*Figure 14: Last part of the last stage*

With the help of CyberChef, we can apply the same technique as shown in the second part of the final stage to retrieve the values inside the two variables and see what they really are.

The first variable is a DLL:

The second variable is an EXE:

By running both in the ANY.RUN sandbox, it is possible to gather information about the C2, ports, certificates, mutex, and more.

*Figure 17: Text report generated by ANY.RUN sandbox*

Learn to analyze cyber threats

See a detailed guide to using ANY.RUN’s Interactive Sandbox for malware and phishing analysis

Read full guide

Second Technique

Open Directory

The structure of the second open directory mirrors the first, containing two files: a TXT file and a JPG file.

The TXT file, with a shorter name, is a VBS script, while the JPG file hides a PowerShell script in disguise.

Analysis of the Txt file

In this case, the TXT file contains a VBS script that is easier to interpret due to its comments. It includes an array storing commands to download the disguised JPG file.

To simplify the script further, we can delete the array and store all the array values in a single variable.

The VBS script then calls cmd to execute PowerShell, which downloads and runs the JPG file.

Analysis of the Powershell file

The PowerShell file performs 2 main functions:

File creation and content writing: Creates three files essential to the infection process

Scheduled task setup: Schedules a task to ensure repeated execution, thereby maintaining the AsyncRAT infection

File Creation

The Powershell creates 3 files.

First file

This obfuscated file stores and executes the values of EXE and DLL files related to AsyncRAT directly in memory.

After cleaning the file, it removes ‘%&%’ from both variables, converts them from hexadecimal, and then loads and executes them into memory.

By carrying out the above-mentioned processes via CyberChef, we get the following results:

Second file

The second file triggers PowerShell to execute the previous file (roox.ps1).

Third file

The third and final file runs the previous file roox.bat while keeping the execution hidden from the victim. This ensures that the infection process remains invisible and minimizes any visible indicators, making it harder for the victim to detect the ongoing activity.

Scheduled Task

The scheduled task, named thepiratMicrosoftEdgeUpdateTask, executes roox.vbs every two minutes, ensuring that the infection persists.

Upon running the PowerShell script inside the ANY.RUN sandbox, we can see the files being created and executed. We can also gather more information about the command and control (C2) infrastructure.

*Figure 28: Files created by the Powershell script*

Figure 29: C2 Ip and DNS

Conclusion

Our investigation uncovered two IPs actively spreading AsyncRAT through different methods. The first method follows a multi-stage process, employing several files and scripts to complete the infection.

The second method uses only two stages, one of which involves generating files that are triggered by a scheduled task, as shown in the image below:

*Figure 30: Difference between two methods*

About ANY.RUN

ANY.RUN helps more than 500,000 cybersecurity professionals worldwide. Our interactive sandbox simplifies malware analysis of threats that target both Windows and Linux systems. Our threat intelligence products, TI Lookup, YARA Search and Feeds, help you find IOCs or files to learn more about the threats and respond to incidents faster.

With ANY.RUN you can:

Detect malware in seconds
Interact with samples in real time
Save time and money on sandbox setup and maintenance
Record and study all aspects of malware behavior
Collaborate with your team
Scale as you need

Request free trial of ANY.RUN’s products →

IOCs

23.26.108.141	Open Directory IP
fsp.txt	7b73596346a36f83b6b540bfc2b779fec228a050e6d7de631d0518b526b9b128
zohre.jpg	561bb05d2c67fe221646b5af653ef7d1e7e552e6745f980385bd344d8155df0f
AsyncRAT.exe	70733e5f26a5b4d8c3d2bcc9a21cd015cee63dc0f93c819e7c401237f69967fe
AsyncRAT.dll	2c6c4cd045537e2586eab73072d790af362e37e6d4112b1d01f15574491296b8
storeroot[.]duckdns[.]org	Command and Control
45.126.208.245	Open Directory IP
nkXhhzeT6H6bxJcU.txt	20b15104f0afc362126f43c0b8628bced3cdecec768bcde79e60ff094c108f8a
aaaNOOTKiiiLAViiiiOOs.bat	73e945f14db13a00fe72b5c2a20233e3bb98816bb31d035e0776b92246f681bc
KiLOvBeRNdautESaatnENn.ps1	f0d190d78b3ed7d83cc30224cd55bc158bdd5c40ec7b1f0108ee27afa1996ab1
KKguLavTEsaaEtneeNARdeP.ps1	29e93b2eac97547386f435811ccf0531ad0df62fd5f021e7e5ea90b2f1f2d69a
KKKKKKllLavIOOOOOtesAA.bat	d5ca45ab8c9c9e6f932e9500836bd8cd725c4739dafe80a5d41e29389c3d69f3
TesKKKeLAvaYdAfbBS.vbs	b1b67754391f0598e86254ad8c3a5741b70472138c1fa1be439be788c682345e
UhLQoyDAMaCUTPaE.vbs	2b312c476ccf036b5339f023a732ddf1aef3f193f59b304ba8089872bae47540
AsyncRAT.exe	d4edb13aa499b39b74912a30c22a1cba6d00694dcb68fa542bdc3d9ab2b66f68
AsyncRAT.dll	5b1b7bd1fadfc3d2abcd8ea8f863fe96233e1dac8b994311c6a331179243b5cd
anothonesevenfivesecsned[.]ddns[.]net	Command and Control

The post AsyncRAT’s Infection Tactics
via Open Directories: Technical Analysis appeared first on ANY.RUN's Cybersecurity Blog.