Threat intelligence / Technique

Compiled HTML File

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. (Citation: Microsoft HTML Help May 2018) CHM content is displayed using underlying components of the Internet Explorer browser (Citation: Microsoft HTML Help ActiveX) loaded by the HTML Help executable program (hh.exe). (Citation: Microsoft HTML Help Executable Program) A custom CHM file containing embedded payloads could be delivered to a victim then triggered by [User Execution](https://attack.mitre.org/techniques/T1204). 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. (Citation: MsitPros CHM Aug 2017) (Citation: Microsoft CVE-2017-8625 Aug 2017)

Technique

TypeTechnique

External ID—

First seen2026-08-14

Last seen2026-08-14

Confidence

—

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. (Citation: Microsoft HTML Help May 2018) CHM content is displayed using underlying components of the Internet Explorer browser (Citation: Microsoft HTML Help ActiveX) loaded by the HTML Help executable program (hh.exe). (Citation: Microsoft HTML Help Executable Program) A custom CHM file containing embedded payloads could be delivered to a victim then triggered by [User Execution](https://attack.mitre.org/techniques/T1204). 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. (Citation: MsitPros CHM Aug 2017) (Citation: Microsoft CVE-2017-8625 Aug 2017)

11 recorded

Relationships

mapped-to

from Hiding Malicious Data or Code within Files

Technique

mitigates

from Execution Prevention

Mitigation

mitigates

from Restrict Web-Based Content

Mitigation

revoked-by

from Compiled HTML File

Technique

subtechnique-of

to System Binary Proxy Execution

Technique

uses

from APT38

Group

uses

from APT41

Group

uses

Malware

uses

from Dark Caracal

Group

uses

Group

uses

Group

6 external

References

mitre-attack

T1218.001

Microsoft CVE-2017-8625 Aug 2017

https://web.archive.org/web/20250419140549/https://msrc.microsoft.com/update-guide/en-US/advisory/CVE-2017-8625

Microsoft HTML Help May 2018

https://docs.microsoft.com/previous-versions/windows/desktop/htmlhelp/microsoft-html-help-1-4-sdk

Microsoft HTML Help Executable Program

https://msdn.microsoft.com/windows/desktop/ms524405

Microsoft HTML Help ActiveX

https://msdn.microsoft.com/windows/desktop/ms644670

MsitPros CHM Aug 2017

https://oddvar.moe/2017/08/13/bypassing-device-guard-umci-using-chm-cve-2017-8625/