tfMITRE ATT&CK sub-technique

Regsvcs/Regasm T1218.009

sub-technique of T1218 System Binary Proxy Execution

Tactic: Stealth
Platform: Windows
Version: 3.0
Created: 23 January 2020
Last modified: 12 May 2026
Contributor: Casey Smith

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. [1] [2]

ReconResource DevInitial AccessExecutionPersistencePriv EscStealthDef ImpairmentCred AccessDiscoveryLateral MoveCollectionC2ExfiltrationImpact

Threat groupsNone recorded

Threat groupsNone recorded · 29% of ATT&CK techniques have none either.

CampaignsNone recorded

CampaignsNone recorded · 54% of ATT&CK techniques have none either.

Tools & malware44th pct

Tools & malware44th percentile · 56% of ATT&CK techniques have more tools implementing them.

Detection rules74th pct

Detection rules74th percentile · 74% of ATT&CK techniques have this many detection rules written or fewer.

Regsvcs/Regasm MITRE reference T1218.009

44th pctamong all ATT&CK techniques for number of tools

1 software entry is documented implementing this technique. MITRE files each as a tool or as malware; newest first, then by how many groups carry them.

Agent TeslaS0331 ↗

Has dropped RegAsm.exe onto systems for performing malicious activity.1

created 2019-01-29MALWAREcarried by 2 groups

All 1 software entries for this technique

Offense vs defense T1218.009

Is defensive coverage keeping up with adversary use? Eight counts, each ranked against all 697 ATT&CK techniques. Attack sits left, defense right, so a shape leaning left means adversaries are better documented here than defenders are equipped. Hover any spoke for its percentile and the share of techniques that have more. The timeline below shows when each side arrived.

How it got here

Range

Adversary activity (campaign spans) over cumulative rule output. Each source is plotted independently from zero, so neither line includes the other. Campaign dates are year-granularity.

Campaigns · 0Sigma rules (cumulative) · 4Splunk ESCU (cumulative) · 6

first rule: 2021 Q1

Regsvcs/Regasm detection strategy DET0361

MITRE names one behaviour worth catching for this technique and breaks it into 1 analytic, one per platform. Each carries the log sources it needs and the fields you tune per environment.

Detecting .NET COM Registration Abuse via Regsvcs/Regasm

Enterprise

1 platform

AN1028 · Windows

Abuse of Regsvcs.exe or Regasm.exe to execute arbitrary code embedded in .NET assemblies via [ComRegisterFunction]/[ComUnregisterFunction]. Behavioral chain: (1) Process creation of regsvcs/regasm with suspicious assembly paths/flags → (2) Assembly/DLL load inside regsvcs/regasm → (3) Registry writes to HKCR\CLSID/ProgID during COM registration → (4) Optional child process or network activity spawned by installer/registration code.

Log sources

The data this analytic draws on. You do not need every component — each one you already collect covers part of it. Each links to its ATT&CK record.

Data component	Name	Channel
Module LoadDC0016	WinEventLog:Sysmon	EventCode=7
Process CreationDC0032	WinEventLog:Security	EventCode=4688
File CreationDC0039	WinEventLog:Sysmon	EventCode=11
Windows Registry Key CreationDC0056	WinEventLog:Sysmon	EventCode=12
Windows Registry Key ModificationDC0063	WinEventLog:Sysmon	EventCode=13, 14
Command ExecutionDC0064	WinEventLog:PowerShell	EventCode=4103, 4104, 4105, 4106
Network Connection CreationDC0082	WinEventLog:Sysmon	EventCode=3, 22

Tunable fields

MITRE calls these the analytic’s mutable elements: the thresholds and filters you set for your own environment.

Field	What you tune
AssemblyPathRegex	Environment-specific paths to flag (e.g., %TEMP%, Downloads, OneDrive, SMB shares). Helps suppress known-good installers.
SuspiciousFlags	Arguments like /unregister (/u), /codebase, /regfile which may indicate abuse. Tune per enterprise use of regasm/regsvcs.
ParentProcessAllowList	Legitimate parents (e.g., setup.exe, msiexec.exe). Analyst can prune false positives from Office or script hosts.
KnownGoodAssemblies	Hashes or publisher info for approved assemblies commonly registered in the environment.
RegistryKeyAllowList	Approved CLSIDs/ProgIDs written during sanctioned software installs.
TimeWindow	Correlation window (e.g., 5–10 min) between file drop → regasm/regsvcs exec → registry writes → child activity.
SignedToUnsignedTransition	Alert if Microsoft-signed regasm/regsvcs loads or triggers unsigned assemblies/children.

Tests2Executorscmd 1 · PowerShell 1Need elevation1 of 2Have prerequisites2Have cleanup2Platformswindows

Test

Platform

Executor

Elevation

Prereqs

Cleanup

Ref

Regasm Uninstall Method Call Test

windows

cmd

—

Yes

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

Input arguments

Name	Type	Default	Description
output_file	path	%tmp%\T1218.009.dll	Location of the payload
source_file	path	PathToAtomicsFolder\T1218.009\src\T1218.009.cs	Location of the CSharp source_file

Attack command

C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /r:System.EnterpriseServices.dll /out:"#{output_file}" /target:library "#{source_file}"
C:\Windows\Microsoft.NET\Framework\v4.0.30319\regasm.exe /U #{output_file}

Cleanup command

del #{output_file} >nul 2>&1

Prerequisite

The CSharp source file must exist on disk at specified location (#{source_file})

Check

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

Satisfy

New-Item -Type Directory (split-path "#{source_file}") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1218.009/src/T1218.009.cs" -OutFile "#{source_file}"

GUID8d3f925c-7701-4583-a0d5-b4994002f09f

Regsvcs Uninstall Method Call Test

windows

PowerShell

Required

Yes

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.

Input arguments

Name	Type	Default	Description
output_file	path	$Env:TEMP\T1218.009.dll	Location of the payload
source_file	path	PathToAtomicsFolder\T1218.009\src\T1218.009.cs	Location of the CSharp source_file

Attack command

$key = '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'
$Content = [System.Convert]::FromBase64String($key)
Set-Content $env:Temp\key.snk -Value $Content -Encoding Byte
C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /r:System.EnterpriseServices.dll /out:"#{output_file}" /target:library /keyfile:$env:Temp\key.snk #{source_file}
C:\Windows\Microsoft.NET\Framework\v4.0.30319\regsvcs.exe #{output_file}

Cleanup command

Remove-Item #{output_file} -ErrorAction Ignore | Out-Null
$parentpath = Split-Path -Path "#{output_file}"
Remove-Item $parentpath\key.snk -ErrorAction Ignore | Out-Null
Remove-Item $parentpath\T1218.009.tlb -ErrorAction Ignore | Out-Null

Prerequisite

The CSharp source file must exist on disk at specified location (#{source_file})

Check

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

Satisfy

New-Item -Type Directory (split-path "#{source_file}") -ErrorAction ignore | Out-Null
Invoke-WebRequest "https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1218.009/src/T1218.009.cs" -OutFile "#{source_file}"

GUIDc582afd8-e25a-4398-91de-9ed8b34c5c51

Tests from Atomic Red Team (MIT licence) · technique definition

Regsvcs/Regasm detections T1218.009

10 rules are mapped to this technique. Parent techniques also include their sub-techniques’ rules. Click a slice or key entry to filter the table.

74th pctamong all ATT&CK techniques for number of rules

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