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T1218.004 InstallUtil · cyberstrikeus | DecimalAI

securityby cyberstrikeus

T1218.004 InstallUtil

cyberstrikeus/T1218.004_installutil

Source cyberstrikeus/cyberstrike ↗License AGPL-3.0

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

SkillScore77Maintained

Automatic

Security & AppSec pack

Last verified 8/13/2026

What it changes

Passed 16 of 21 test cases with the skill, and 10 of 21 without it.

Without skill45%

With skill77%

Checks it passed that the model alone missed

Expects Constructor_ as the actual output string.
Specifies Constructor_ as the expected output string.
Includes /action=install in the command line parameters.

and 10 more in the full report

7 fixed10 passed either way5 still failing0 broke

Pass-rate lift: +32 pp
Tokens: +82%
Agent turns: 0%
Response time: -39%

Model gemini-3.6-flashMeasured 8/13/2026v117 of 22 cases passed with skill · 21 comparable

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/cyberstrikeus-t1218-004-installutil/SKILL.md https://app.decimal.ai/s/cyberstrikeus-t1218-004-installutil/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add cyberstrikeus-t1218-004-installutil, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/cyberstrikeus-t1218-004-installutil/ and pins it in .decimal/skills.lock

decimalai skills add cyberstrikeus-t1218-004-installutil

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/cyberstrikeus-t1218-004-installutil/SKILL.md https://app.decimal.ai/s/cyberstrikeus-t1218-004-installutil/SKILL.md

Raw file: /s/cyberstrikeus-t1218-004-installutil/SKILL.md ↗ · machine-readable summary at /s/cyberstrikeus-t1218-004-installutil.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 6 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 6

Prompt

Before executing any of the PowerShell atomic tests for InstallUtil, what critical dependency function must be available in the execution environment?

What was checked, without and with the skill
Checked	Without skill	With skill
Requires importing the test harness script containing Invoke-BuildAndInvokeInstallUtilAssembly.	Missed	Passed

case-21 · gemini-3.6-flash · 8/13/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md266 linessingle file

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}"

Track record

Benchmark

16 / 21

test cases passed, vs 10 / 21 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

cyberstrikeus / cyberstrike

.cyberstrike/skill/mitre_attack/TA0005_defense-evasion/T1218.004_installutil/SKILL.md

View on GitHub ↗

License AGPL-3.0Imported 8/3/2026Version v1

More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

T1218.004 InstallUtil

High-Level Description

Kill Chain Phase

What to Check

How to Test

Atomic Red Team Tests

Atomic Test 1: CheckIfInstallable method call

Track record

Benchmark

Adoption

SkillSafety

Source

Related skills