Infected PowerPoint Files Using Cloud Services to Deliver Multiple
Malware
By Gustavo Palazolo
Published: 2022-01-24 · Archived: 2026-04-06 00:56:07 UTC
Co-authored by Gustavo Palazolo and Ghanashyam Satpathy
Summary
In 2021, malicious Office documents accounted for 37% of all malware downloads detected by Netskope,
showing favoritism for this infection vector among attackers. This is likely due to the ubiquitous usage of
Microsoft Office in enterprises across the globe. Throughout 2021 we have analyzed many techniques used by
attackers to deliver payloads through infected documents, which included the return of Emotet, a campaign that
primarily uses infected documents to spread malware.
Since December 2021, Netskope Threat Labs has observed an increase in the usage of one specific file type from
the Microsoft Office suite: PowerPoint. These relatively small files are being delivered through phishing emails,
then downloading and executing malicious scripts through LoLBins, a common technique often used to stay under
the radar. 
We spotted this campaign delivering multiple malware, such as AveMaria (a.k.a. Warzone) and AgentTesla. These
files are using Bitly to shorten URLs and different cloud services like MediaFire, Blogger, and GitHub to host the
payloads. In this blog post, we will analyze a malicious PowerPoint Add-In file detected by Netskope that delivers
multiple malware, including AgentTesla.
Stage 01 – Infected PowerPoint File
The infection flow starts with a phishing email that carries the infected file as an attachment, along with a message
that lures the victim to download and open it.
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Phishing email with a malicious attachment.
The file is fairly small and it doesn’t contain anything but the malicious VBA macro.
Infected PowerPoint file.
The macro is obfuscated and it uses an internal function to decrypt important strings at runtime.
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Obfuscated VBA code within the infected PowerShell file.
The script deobfuscation is straightforward and leads to the following VBA code.
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Command executed by the malicious PowerShell file.
This technique uses Outlook (COM Object) to execute PowerShell, which bypasses the child process created by
PowerPoint.
PowerShell spawned by Outlook’s process.
The script is executed with a combination of PowerShell and mshta, a similar technique employed by
BazarLoader.
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Malicious script being executed through LoLBins.
Stage 02 – VBS File
The URL contacted by the mshta binary is shortened through the Bitly domain “j.mp”, and the payload is hosted
on MediaFire, a cloud service for file storage and sharing.
The next stage is a VBS script that is lightly obfuscated within an HTML page, which is decoded and executed
through a simple JavaScript function.
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Second stage executed by the infected PowerPoint file.
Once deobfuscated, the VBS script performs multiple tasks to:
1. Create a persistence mechanism through the Windows registry to execute two PowerShell scripts from
external URLs. The first script delivers AgentTesla, and the second script is used to disable some OS
defenses, such as Windows Defender.
2. Create a scheduled task that executes a script from an external URL through mshta approximately every
hour. This script delivers a cryptocurrency stealer developed in PowerShell, hidden within a fake web page
hosted with Blogger.
3. Create a persistence mechanism through the Windows registry to execute a script from an external URL
using mshta. Unfortunately, we can’t tell what was being executed as this URL was offline at the time of
the analysis.
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Malicious VBS responsible for the next stages.
Stage 03 – AgentTesla
The first PowerShell script is responsible for executing AgentTesla, which is a .NET-based Remote Access Trojan
with many capabilities, such as stealing browser’s passwords, capturing keystrokes, clipboard, etc.
The code is slightly obfuscated, protecting variables, function names, and strings. There are two large arrays that
contain:
1. Compressed bytes of AgentTesla;
2. Compressed bytes of a .NET Injector used for process injection;
None of the executables are written to disk, which characterizes this attack as fileless.
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PowerShell script responsible for executing AgentTesla.
Once both files are decompressed, the script loads the injector and calls a function named “Execute”, responsible
for injecting AgentTesla payload into an instance of “aspnet_compiler.exe”, which is a binary from the .NET
framework.
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Removing a minor obfuscation in the PowerShell script, showing how the payload gets executed.
Most of the injector’s function names are obfuscated, but we can see the namespace, the class, and the method that
is being called to inject AgentTesla into a process. Furthermore, an injector using “projFUD” as namespace was
previously spotted in the wild, used by other malware such as ASyncRAT and RevengeRAT.
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Injector’s decompiled code.
AgentTesla is developed in .NET and this sample is using a protector known as “Obfuscar”, which creates a few
mechanisms in the code to make analysis harder.
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AgentTesla sample delivered by the infected PowerPoint file.
Despite the protector’s usage, it’s still possible to see clean code from the decompiler, like this method that sends
HTTP requests.
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Function used by AgentTesla for network requests.
All the strings used by AgentTesla are encrypted within the binary, where all the characters are stored in a single
array of bytes. Once it’s running, the code decrypts all the characters in the list using a simple XOR operation with
the encrypted byte, its position on the list, and the decimal 170.  Whenever AgentTesla needs to access a string, it
calls a function that returns the string by accessing its position in the list, and the respective length.
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AgentTesla string encryption scheme.
Using the same logic, we can use a combination of regex and a Python script to decrypt all the strings in the
binary. The complete list of decrypted strings can be found on our Github page.
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Decrypted strings from AgentTesla.
Furthermore, AgentTesla sends an HTTP POST request to a malicious server with information about the infected
machine, such as the computer name, username, IP address, etc.
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AgentTesla HTTP request.
Stage 04 – PowerShell
The second PowerShell file executed by the VBS script in the second stage is mostly used to disable Windows
Defender.
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PowerShell downloading the payloads.
Once running, it downloads a file from GitHub named NSudo, which is used for privilege escalation (TA0004).
NSudo is executed as “TrustedInstaller” through the arguments  “-U:T”.
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GUI from downloaded file “NSudo”.
The second download is a VBS script hosted on MediaFire, which uses NSudo and other commands to disable
Windows Defender and to add a few AV exclusions based on file extensions, paths, and executable names.
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VBS downloaded by PowerShell.
The VBS is executed through another Living-off-the-Land technique, by first creating an INF file with the
command to be executed.
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PowerShell creating INF file.
And then executing the INF file with the cmstp LoLBin.
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Executing the INF file.
Stage 05 – Cryptocurrency Stealer
The third URL downloaded by the second stage VBS is hosted with Blogger, which tries to camouflage itself
through a fake web page that says the content is sensitive.
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Fake web page downloaded by the second stage.
Despite the attempt to hide behind this web page, we can find two malicious VBS within the HTML, which are
decoded and executed with a simple JavaScript.
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VBS code hidden in the HTML page.
One of the VBS executed in this stage leads to the same PowerShell that delivers AgentTesla, which is redundant.
However, the other VBS code leads to a simple cryptocurrency stealer written in PowerShell.
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VBS loading and executing the cryptocurrency stealer.
The malware is fairly simple, it works by checking the clipboard data with a regex that matches the
cryptocurrency wallet pattern. If it is found, the data is replaced with the attacker’s wallet address.
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Cryptocurrency stealer in PowerShell.
The code is able to replace the address for many coins, such as Bitcoin, Ethereum, XMR, DOGE, etc.
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Cryptocurrency addresses used by the attacker.
The complete list of the addresses used by the attacker can be found on our GitHub page.
Conclusion
Attackers not only continue to abuse Microsoft Office to deliver malware, but are also increasingly including
cloud services in their attacks, as this adds a certain resilience to the entire process. Netskope Advanced Threat
Protection includes a custom Microsoft Office file analyzer and a sandbox to detect campaigns like the one we
described in this analysis. We will continue to provide updates on this threat as it evolves.
Protection
Netskope Threat Labs is actively monitoring this campaign and has ensured coverage for all known threat
indicators and payloads.
Netskope Threat Protection
Document-Office.Trojan.AgentTesla
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Win32.Trojan.AgentTesla
Netskope Advanced Threat Protection provides proactive coverage against this threat.
Gen.Malware.Detect.By.StHeur indicates a sample that was detected using static analysis
Gen.Malware.Detect.By.Sandbox indicates a sample that was detected by our cloud sandbox
Gen.Malware.Detect.By.StHeur.MsOffice indicates a sample that was detected by Netskope’s static ML
Microsoft Office analyzer engine.
Below we have an example of a sample detected by Netskope, which has a score of 9/63 on VirusTotal.
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IOCs
A full list of IOCs and a Yara rule are all available in our GitHub repo.
Source: https://www.netskope.com/blog/infected-powerpoint-files-using-cloud-services-to-deliver-multiple-malware
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