T1218.004_installutil

Adversaries may use InstallUtil to proxy execution of code through a trusted Windows utility.

cyberstrikeus Updated Sep 17, 2026

Coding & Dev Tools

Install

Press C to copy

$ npx skillmds@latest add cyberstrikeus/t1218-004-installutil

Installs into ~/.claude/skills (or .claude/skills inside a project). Restart Claude Code to pick it up.

Download SKILL.md

＋ Add to collection

README badge

[![SkillMD](https://skillmd.com/badge/cyberstrikeus/t1218-004-installutil.svg)](https://skillmd.com/skills/cyberstrikeus/t1218-004-installutil)

Trust & safety

3 of 3 audits passed

Last audited Sep 19, 2026 · commit c179788

Works with: Claude Code Claude.ai OpenAI Codex +

File contents

T1218.004 InstallUtil

Sub-technique of: T1218

High-Level Description

Adversaries may use InstallUtil to proxy execution of code through a trusted Windows utility. InstallUtil is a command-line utility that allows for installation and uninstallation of resources by executing specific installer components specified in .NET binaries. The InstallUtil binary may also be digitally signed by Microsoft and located in the .NET directories on a Windows system: C:\Windows\Microsoft.NET\Framework\v\InstallUtil.exe and C:\Windows\Microsoft.NET\Framework64\v\InstallUtil.exe.

InstallUtil may also be used to bypass application control through use of attributes within the binary that execute the class decorated with the attribute [System.ComponentModel.RunInstaller(true)].

Kill Chain Phase

Defense Evasion (TA0005)

Platforms: Windows

What to Check

Identify if InstallUtil technique is applicable to target environment
Check Windows systems for indicators of InstallUtil
Verify mitigations are bypassed or absent (2 known mitigations)
Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: CheckIfInstallable method call

Executes the CheckIfInstallable class constructor runner instead of executing InstallUtil. Upon execution, the InstallUtil test harness will be executed. If no output is displayed the test executed successfuly.

Supported Platforms: windows

# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly
. "#{test_harness}"

$InstallerAssemblyDir = "#{assembly_dir}"
$InstallerAssemblyFileName = "#{assembly_filename}"
$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName

$ExpectedOutput = 'Constructor_'

$TestArgs = @{
    OutputAssemblyDirectory = $InstallerAssemblyDir
    OutputAssemblyFileName = $InstallerAssemblyFileName
    InvocationMethod = '#{invocation_method}'
}

$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs -MinimumViableAssembly

if ($ActualOutput -ne $ExpectedOutput) {
    throw @"
CheckIfInstallable method execution test failure. Installer assembly execution output did not match the expected output.
Expected: $ExpectedOutput
Actual: $ActualOutput
"@
}

Dependencies:

InstallUtil test harness script must be installed at specified location (#{test_harness})

Atomic Test 2: InstallHelper method call

Executes the InstallHelper class constructor runner instead of executing InstallUtil. Upon execution, no output will be displayed if the test executed successfuly.

Supported Platforms: windows

# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly
. "#{test_harness}"

$InstallerAssemblyDir = "#{assembly_dir}"
$InstallerAssemblyFileName = "#{assembly_filename}"
$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName

$CommandLine = "/logfile= /logtoconsole=false `"$InstallerAssemblyFullPath`""
$ExpectedOutput = 'Constructor_'

$TestArgs = @{
    OutputAssemblyDirectory = $InstallerAssemblyDir
    OutputAssemblyFileName = $InstallerAssemblyFileName
    InvocationMethod = '#{invocation_method}'
    CommandLine = $CommandLine
}

$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs -MinimumViableAssembly

if ($ActualOutput -ne $ExpectedOutput) {
    throw @"
InstallHelper method execution test failure. Installer assembly execution output did not match the expected output.
Expected: $ExpectedOutput
Actual: $ActualOutput
"@
}

Dependencies:

InstallUtil test harness script must be installed at specified location (#{test_harness})

Atomic Test 3: InstallUtil class constructor method call

Executes the installer assembly class constructor. Upon execution, version information will be displayed the .NET framework install utility.

Supported Platforms: windows

# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly
. "#{test_harness}"

$InstallerAssemblyDir = "#{assembly_dir}"
$InstallerAssemblyFileName = "#{assembly_filename}"
$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName

$CommandLine = "/logfile= /logtoconsole=false `"$InstallerAssemblyFullPath`""
$ExpectedOutput = 'Constructor_'

$TestArgs = @{
    OutputAssemblyDirectory = $InstallerAssemblyDir
    OutputAssemblyFileName = $InstallerAssemblyFileName
    InvocationMethod = '#{invocation_method}'
    CommandLine = $CommandLine
}

$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs -MinimumViableAssembly

if ($ActualOutput -ne $ExpectedOutput) {
    throw @"
InstallUtil class constructor execution test failure. Installer assembly execution output did not match the expected output.
Expected: $ExpectedOutput
Actual: $ActualOutput
"@
}

Dependencies:

InstallUtil test harness script must be installed at specified location (#{test_harness})

Atomic Test 4: InstallUtil Install method call

Executes the Install Method. Upon execution, version information will be displayed the .NET framework install utility.

Supported Platforms: windows

# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly
. "#{test_harness}"

$InstallerAssemblyDir = "#{assembly_dir}"
$InstallerAssemblyFileName = "#{assembly_filename}"
$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName

$CommandLine = "/logfile= /logtoconsole=false /installtype=notransaction /action=install `"$InstallerAssemblyFullPath`""
$ExpectedOutput = 'Constructor_Install_'

$TestArgs = @{
    OutputAssemblyDirectory = $InstallerAssemblyDir
    OutputAssemblyFileName = $InstallerAssemblyFileName
    InvocationMethod = '#{invocation_method}'
    CommandLine = $CommandLine
}

$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs

if ($ActualOutput -ne $ExpectedOutput) {
    throw @"
InstallUtil Install method execution test failure. Installer assembly execution output did not match the expected output.
Expected: $ExpectedOutput
Actual: $ActualOutput
"@
}

Dependencies:

InstallUtil test harness script must be installed at specified location (#{test_harness})

Atomic Test 5: InstallUtil Uninstall method call - /U variant

Executes the Uninstall Method. Upon execution, version information will be displayed the .NET framework install utility.

Supported Platforms: windows

# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly
. "#{test_harness}"

$InstallerAssemblyDir = "#{assembly_dir}"
$InstallerAssemblyFileName = "#{assembly_filename}"
$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName

$CommandLine = "/logfile= /logtoconsole=false /U `"$InstallerAssemblyFullPath`""
$ExpectedOutput = 'Constructor_Uninstall_'

$TestArgs = @{
    OutputAssemblyDirectory = $InstallerAssemblyDir
    OutputAssemblyFileName = $InstallerAssemblyFileName
    InvocationMethod = '#{invocation_method}'
    CommandLine = $CommandLine
}

$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs

if ($ActualOutput -ne $ExpectedOutput) {
    throw @"
InstallUtil Uninstall method execution test failure. Installer assembly execution output did not match the expected output.
Expected: $ExpectedOutput
Actual: $ActualOutput
"@
}

Dependencies:

InstallUtil test harness script must be installed at specified location (#{test_harness})

Manual Testing

If Atomic Red Team tests are not applicable, manually verify the technique by:

Identify Attack Surface: Determine if the target environment is susceptible to InstallUtil by examining the target platforms (Windows).
Assess Existing Defenses: Review whether mitigations for T1218.004 are in place. If defenses are absent or misconfigured, this technique may be exploitable.
Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.

Remediation Guide

M1038 Execution Prevention

Use application control configured to block execution of InstallUtil.exe if it is not required for a given system or network to prevent potential misuse by adversaries.

M1042 Disable or Remove Feature or Program

InstallUtil may not be necessary within a given environment.

Detection

Detection of Malicious Code Execution via InstallUtil.exe

Risk Assessment

Finding	Severity	Impact
InstallUtil technique applicable	Medium	Defense Evasion

CWE Categories

CWE ID	Title
CWE-693	Protection Mechanism Failure

References

---name: t1218-004-installutildescription: Adversaries may use InstallUtil to proxy execution of code through a trusted Windows utility.---# T1218.004 InstallUtil> **Sub-technique of:** T1218## High-Level DescriptionAdversaries may use InstallUtil to proxy execution of code through a trusted Windows utility. InstallUtil is a command-line utility that allows for installation and uninstallation of resources by executing specific installer components specified in .NET binaries. The InstallUtil binary may also be digitally signed by Microsoft and located in the .NET directories on a Windows system: <code>C:\Windows\Microsoft.NET\Framework\v<version>\InstallUtil.exe</code> and <code>C:\Windows\Microsoft.NET\Framework64\v<version>\InstallUtil.exe</code>.InstallUtil may also be used to bypass application control through use of attributes within the binary that execute the class decorated with the attribute <code>[System.ComponentModel.RunInstaller(true)]</code>.## Kill Chain Phase- Defense Evasion (TA0005)**Platforms:** Windows## What to Check- [ ] Identify if InstallUtil technique is applicable to target environment- [ ] Check Windows systems for indicators of InstallUtil- [ ] Verify mitigations are bypassed or absent (2 known mitigations)- [ ] Assess detection coverage (1 detection strategies)## How to Test### Atomic Red Team TestsThe following tests are from [Atomic Red Team](https://github.com/redcanaryco/atomic-red-team) and provide actionable ways to test this technique:### Atomic Test 1: CheckIfInstallable method callExecutes the CheckIfInstallable class constructor runner instead of executing InstallUtil. Upon execution, the InstallUtil test harness will be executed.If no output is displayed the test executed successfuly.**Supported Platforms:** windows```powershell# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly. "#{test_harness}"$InstallerAssemblyDir = "#{assembly_dir}"$InstallerAssemblyFileName = "#{assembly_filename}"$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName$ExpectedOutput = 'Constructor_'$TestArgs = @{ OutputAssemblyDirectory = $InstallerAssemblyDir OutputAssemblyFileName = $InstallerAssemblyFileName InvocationMethod = '#{invocation_method}'}$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs -MinimumViableAssemblyif ($ActualOutput -ne $ExpectedOutput) { throw @"CheckIfInstallable method execution test failure. Installer assembly execution output did not match the expected output.Expected: $ExpectedOutputActual: $ActualOutput"@}```**Dependencies:**- InstallUtil test harness script must be installed at specified location (#{test_harness})### Atomic Test 2: InstallHelper method callExecutes the InstallHelper class constructor runner instead of executing InstallUtil. Upon execution, no output will be displayed if the testexecuted successfuly.**Supported Platforms:** windows```powershell# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly. "#{test_harness}"$InstallerAssemblyDir = "#{assembly_dir}"$InstallerAssemblyFileName = "#{assembly_filename}"$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName$CommandLine = "/logfile= /logtoconsole=false `"$InstallerAssemblyFullPath`""$ExpectedOutput = 'Constructor_'$TestArgs = @{ OutputAssemblyDirectory = $InstallerAssemblyDir OutputAssemblyFileName = $InstallerAssemblyFileName InvocationMethod = '#{invocation_method}' CommandLine = $CommandLine}$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs -MinimumViableAssemblyif ($ActualOutput -ne $ExpectedOutput) { throw @"InstallHelper method execution test failure. Installer assembly execution output did not match the expected output.Expected: $ExpectedOutputActual: $ActualOutput"@}```**Dependencies:**- InstallUtil test harness script must be installed at specified location (#{test_harness})### Atomic Test 3: InstallUtil class constructor method callExecutes the installer assembly class constructor. Upon execution, version information will be displayed the .NET framework install utility.**Supported Platforms:** windows```powershell# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly. "#{test_harness}"$InstallerAssemblyDir = "#{assembly_dir}"$InstallerAssemblyFileName = "#{assembly_filename}"$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName$CommandLine = "/logfile= /logtoconsole=false `"$InstallerAssemblyFullPath`""$ExpectedOutput = 'Constructor_'$TestArgs = @{ OutputAssemblyDirectory = $InstallerAssemblyDir OutputAssemblyFileName = $InstallerAssemblyFileName InvocationMethod = '#{invocation_method}' CommandLine = $CommandLine}$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgs -MinimumViableAssemblyif ($ActualOutput -ne $ExpectedOutput) { throw @"InstallUtil class constructor execution test failure. Installer assembly execution output did not match the expected output.Expected: $ExpectedOutputActual: $ActualOutput"@}```**Dependencies:**- InstallUtil test harness script must be installed at specified location (#{test_harness})### Atomic Test 4: InstallUtil Install method callExecutes the Install Method. Upon execution, version information will be displayed the .NET framework install utility.**Supported Platforms:** windows```powershell# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly. "#{test_harness}"$InstallerAssemblyDir = "#{assembly_dir}"$InstallerAssemblyFileName = "#{assembly_filename}"$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName$CommandLine = "/logfile= /logtoconsole=false /installtype=notransaction /action=install `"$InstallerAssemblyFullPath`""$ExpectedOutput = 'Constructor_Install_'$TestArgs = @{ OutputAssemblyDirectory = $InstallerAssemblyDir OutputAssemblyFileName = $InstallerAssemblyFileName InvocationMethod = '#{invocation_method}' CommandLine = $CommandLine}$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgsif ($ActualOutput -ne $ExpectedOutput) { throw @"InstallUtil Install method execution test failure. Installer assembly execution output did not match the expected output.Expected: $ExpectedOutputActual: $ActualOutput"@}```**Dependencies:**- InstallUtil test harness script must be installed at specified location (#{test_harness})### Atomic Test 5: InstallUtil Uninstall method call - /U variantExecutes the Uninstall Method. Upon execution, version information will be displayed the .NET framework install utility.**Supported Platforms:** windows```powershell# Import the required test harness function, Invoke-BuildAndInvokeInstallUtilAssembly. "#{test_harness}"$InstallerAssemblyDir = "#{assembly_dir}"$InstallerAssemblyFileName = "#{assembly_filename}"$InstallerAssemblyFullPath = Join-Path -Path $InstallerAssemblyDir -ChildPath $InstallerAssemblyFileName$CommandLine = "/logfile= /logtoconsole=false /U `"$InstallerAssemblyFullPath`""$ExpectedOutput = 'Constructor_Uninstall_'$TestArgs = @{ OutputAssemblyDirectory = $InstallerAssemblyDir OutputAssemblyFileName = $InstallerAssemblyFileName InvocationMethod = '#{invocation_method}' CommandLine = $CommandLine}$ActualOutput = Invoke-BuildAndInvokeInstallUtilAssembly @TestArgsif ($ActualOutput -ne $ExpectedOutput) { throw @"InstallUtil Uninstall method execution test failure. Installer assembly execution output did not match the expected output.Expected: $ExpectedOutputActual: $ActualOutput"@}```**Dependencies:**- InstallUtil test harness script must be installed at specified location (#{test_harness})### Manual TestingIf Atomic Red Team tests are not applicable, manually verify the technique by:1. **Identify Attack Surface**: Determine if the target environment is susceptible to InstallUtil by examining the target platforms (Windows).2. **Assess Existing Defenses**: Review whether mitigations for T1218.004 are in place. If defenses are absent or misconfigured, this technique may be exploitable.3. **Execute Test**: Use tools and methods described in the MITRE ATT&CK page and external references below.## Remediation Guide### M1038 Execution PreventionUse application control configured to block execution of InstallUtil.exe if it is not required for a given system or network to prevent potential misuse by adversaries.### M1042 Disable or Remove Feature or ProgramInstallUtil may not be necessary within a given environment.## Detection### Detection of Malicious Code Execution via InstallUtil.exe## Risk Assessment| Finding | Severity | Impact || -------------------------------- | -------- | --------------- || InstallUtil technique applicable | Medium | Defense Evasion |## CWE Categories| CWE ID | Title || ------- | ---------------------------- || CWE-693 | Protection Mechanism Failure |## References- [MSDN InstallUtil](https://msdn.microsoft.com/en-us/library/50614e95.aspx)- [LOLBAS Installutil](https://lolbas-project.github.io/lolbas/Binaries/Installutil/)- [Atomic Red Team - T1218.004](https://github.com/redcanaryco/atomic-red-team/tree/master/atomics/T1218.004)- [MITRE ATT&CK - T1218.004](https://attack.mitre.org/techniques/T1218/004)

cyberstrikeus/cyberstrike/tree/main/.cyberstrike/skill/mitre_attack/TA0005_defense-evasion/T1218.004_installutil commit c17978829a

Frequently asked questions

npx skillmds@latest add cyberstrikeus/t1218-004-installutil