System Binary Proxy Execution: Compiled HTML File
- ID
- T1218.001
- Tactics
- TA0005 Stealth
- Sub-technique of
- T1218 System Binary Proxy Execution
- Platforms
- Windows
- Data sources
- Process Creation, File Creation, Module Load, Network Connection Creation
- Source
- attack.mitre.org
- MITRE last modified
- 12 May 2026
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. [1] CHM content is displayed using underlying components of the Internet Explorer browser [2] loaded by the HTML Help executable program (hh.exe). [3]
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. [4] [5]
Detection
- DET0342 Detection of Suspicious Compiled HTML File Execution via hh.exe
Data components: Process Creation, File Creation, Module Load, Network Connection Creation
Mitigations (2)
- M1021 Restrict Web-Based Content
Consider blocking download/transfer and execution of potentially uncommon file types known to be used in adversary campaigns, such as CHM files
- M1038 Execution Prevention
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.