MITRE ATT&CK Technique
Defense Evasion T1223
Description

Compiled HTML files (.chm) 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) Adversaries may abuse this technology to conceal malicious code. 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 whitelisting 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)

Supported Platforms
Windows
Created

April 29, 2026

Last Updated

April 29, 2026

STIX Data
{'created': '2018-10-17T00:14:20.652Z',
 'created_by_ref': 'identity--c78cb6e5-0c4b-4611-8297-d1b8b55e40b5',
 'description': 'Compiled HTML files (.chm) 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)\n'
                '\n'
                'Adversaries may abuse this technology to conceal malicious '
                'code. 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 whitelisting 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)',
 'external_references': [{'external_id': 'T1223',
                          'source_name': 'mitre-attack',
                          'url': 'https://attack.mitre.org/techniques/T1223'},
                         {'description': 'Microsoft. (2018, May 30). Microsoft '
                                         'HTML Help 1.4. Retrieved October 3, '
                                         '2018.',
                          'source_name': 'Microsoft HTML Help May 2018',
                          'url': 'https://docs.microsoft.com/previous-versions/windows/desktop/htmlhelp/microsoft-html-help-1-4-sdk'},
                         {'description': 'Microsoft. (n.d.). HTML Help ActiveX '
                                         'Control Overview. Retrieved October '
                                         '3, 2018.',
                          'source_name': 'Microsoft HTML Help ActiveX',
                          'url': 'https://msdn.microsoft.com/windows/desktop/ms644670'},
                         {'description': 'Microsoft. (n.d.). About the HTML '
                                         'Help Executable Program. Retrieved '
                                         'October 3, 2018.',
                          'source_name': 'Microsoft HTML Help Executable '
                                         'Program',
                          'url': 'https://msdn.microsoft.com/windows/desktop/ms524405'},
                         {'description': 'Moe, O. (2017, August 13). Bypassing '
                                         'Device guard UMCI using CHM – '
                                         'CVE-2017-8625. Retrieved October 3, '
                                         '2018.',
                          'source_name': 'MsitPros CHM Aug 2017',
                          'url': 'https://msitpros.com/?p=3909'},
                         {'description': 'Microsoft. (2017, August 8). '
                                         'CVE-2017-8625 - Internet Explorer '
                                         'Security Feature Bypass '
                                         'Vulnerability. Retrieved October 3, '
                                         '2018.',
                          'source_name': 'Microsoft CVE-2017-8625 Aug 2017',
                          'url': 'https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8625'}],
 'id': 'attack-pattern--d21a2069-23d5-4043-ad6d-64f6b644cb1a',
 'kill_chain_phases': [{'kill_chain_name': 'mitre-attack',
                        'phase_name': 'defense-evasion'},
                       {'kill_chain_name': 'mitre-attack',
                        'phase_name': 'execution'}],
 'modified': '2025-10-24T17:49:25.900Z',
 'name': 'Compiled HTML File',
 'object_marking_refs': ['marking-definition--fa42a846-8d90-4e51-bc29-71d5b4802168'],
 'revoked': True,
 'spec_version': '2.1',
 'type': 'attack-pattern',
 'x_mitre_attack_spec_version': '3.2.0',
 'x_mitre_contributors': ['Rahmat Nurfauzi, @infosecn1nja, PT Xynexis '
                          'International'],
 'x_mitre_deprecated': False,
 'x_mitre_detection': '',
 'x_mitre_domains': ['enterprise-attack'],
 'x_mitre_is_subtechnique': False,
 'x_mitre_modified_by_ref': 'identity--c78cb6e5-0c4b-4611-8297-d1b8b55e40b5',
 'x_mitre_platforms': ['Windows'],
 'x_mitre_version': '1.2'}
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