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Adversaries may abuse Compiled HTML files (.chm) to conceal malicious code.
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macOS post-exploitation for credential harvesting, DTrace monitoring, TCC bypass, and stealth operations via native tools
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Based on SOC occupation classification
| 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"} |
Sub-technique of: T1218
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.
Platforms: Windows
The following tests are from Atomic Red Team and provide actionable ways to test this technique:
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:
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}
Executes a CHM file with the default Shortcut Command method.
windows
Invoke-ATHCompiledHelp -HHFilePath #{hh_file_path} -CHMFilePath #{chm_file_path}
Dependencies:
Executes a CHM file with the ITS protocol handler.
Supported Platforms: windows
Invoke-ATHCompiledHelp -InfoTechStorageHandler #{infotech_storage_handler} -HHFilePath #{hh_file_path} -CHMFilePath #{chm_file_path}
Dependencies:
Executes a CHM file simulating a user double click.
Supported Platforms: windows
Invoke-ATHCompiledHelp -SimulateUserDoubleClick -CHMFilePath #{chm_file_path}
Dependencies:
If Atomic Red Team tests are not applicable, manually verify the technique by:
Identify Attack Surface: Determine if the target environment is susceptible to Compiled HTML File by examining the target platforms (Windows).
Assess Existing Defenses: Review whether mitigations for T1218.001 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.
Consider blocking download/transfer and execution of potentially uncommon file types known to be used in adversary campaigns, such as CHM files
Consider using application control to prevent execution of hh.exe if it is not required for a given system or network to prevent potential misuse by adversaries.
| Finding | Severity | Impact |
|---|---|---|
| Compiled HTML File technique applicable | Low | Defense Evasion |
| CWE ID | Title |
|---|---|
| CWE-693 | Protection Mechanism Failure |