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)

Linked Issues

Issuelinks
Linktype Issue
is related to Techniques
is blocked by Restrict Web-Based Content
is blocked by Execution Prevention
is blocked by Detection of Suspicious Compiled HTML File Execution via hh.exe
is blocked by Secure Baseline Configurations
is blocked by Least Functionality
is blocked by User-Installed Software
is blocked by Continuous Monitoring
is blocked by Malicious Code Protection (Anti-Malware)
is blocked by Endpoint File Integrity Monitoring (FIM)
is blocked by Mobile Code
is blocked by Memory Protection
is blocked by Input Data Validation
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