t1218-001-compiled-html-file

name	T1218.001_compiled-html-file
description	Adversaries may abuse Compiled HTML files (.chm) to conceal malicious code.
category	configuration
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1218.001","defense-evasion","windows","sub-technique"]
technique_id	T1218.001
tactic	defense-evasion
all_tactics	["defense-evasion"]
platforms	["Windows"]
mitre_url	https://attack.mitre.org/techniques/T1218/001
tech_stack	["windows"]
cwe_ids	["CWE-693"]
chains_with	["T1218","T1218.002","T1218.003","T1218.004","T1218.005","T1218.007","T1218.008","T1218.009","T1218.010","T1218.011","T1218.012","T1218.013","T1218.014","T1218.015"]
prerequisites	["T1218"]
severity_boost	{"T1218":"Chain with T1218 for deeper attack path","T1218.002":"Chain with T1218.002 for deeper attack path","T1218.003":"Chain with T1218.003 for deeper attack path"}

T1218.001 Compiled HTML File

Sub-technique of: T1218

High-Level Description

Adversaries may abuse Compiled HTML files (.chm) to conceal malicious code. CHM files are commonly distributed as part of the Microsoft HTML Help system. CHM files are compressed compilations of various content such as HTML documents, images, and scripting/web related programming languages such VBA, JScript, Java, and ActiveX. CHM content is displayed using underlying components of the Internet Explorer browser loaded by the HTML Help executable program (hh.exe).

A custom CHM file containing embedded payloads could be delivered to a victim then triggered by User Execution. CHM execution may also bypass application application control on older and/or unpatched systems that do not account for execution of binaries through hh.exe.

Kill Chain Phase

• Defense Evasion (TA0005)

Platforms: Windows

What to Check

• Identify if Compiled HTML File technique is applicable to target environment
• Check Windows systems for indicators of Compiled HTML File
• 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: Compiled HTML Help Local Payload

Uses hh.exe to execute a local compiled HTML Help payload. Upon execution calc.exe will open

Supported Platforms: windows

hh.exe "#{local_chm_file}"

Dependencies:

• The payload must exist on disk at specified location (#{local_chm_file})

Atomic Test 2: Compiled HTML Help Remote Payload

Uses hh.exe to execute a remote compiled HTML Help payload. Upon execution displays an error saying the file cannot be open

Supported Platforms: windows

hh.exe #{remote_chm_file}

Atomic Test 3: Invoke CHM with default Shortcut Command Execution

Executes a CHM file with the default Shortcut Command method.

windows