Process Activity via Compiled HTML Fileedit

Compiled HTML files (.chm) are commonly distributed as part of the Microsoft HTML Help system. Adversaries may conceal malicious code in a CHM file and deliver it to a victim for execution. CHM content is loaded by the HTML Help executable program (hh.exe).

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-windows.*

Severity: medium

Risk score: 47

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100


  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Execution

Version: 11 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 8.2.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positivesedit

The HTML Help executable program (hh.exe) runs whenever a user clicks a compiled help (.chm) file or menu item that opens the help file inside the Help Viewer. This is not always malicious, but adversaries may abuse this technology to conceal malicious code.

Investigation guideedit

## Config

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.

Rule queryedit

process where event.type in ("start", "process_started") and : "hh.exe" and : ("mshta.exe",
"cmd.exe", "powershell.exe", "pwsh.exe", "powershell_ise.exe",
"cscript.exe", "wscript.exe")

Threat mappingedit


Rule version historyedit

Version 11 (8.2.0 release)
  • Formatting only
Version 10 (7.16.0 release)
  • Updated query, changed from:

    process where event.type in ("start", "process_started") and : "hh.exe" and : ("mshta.exe",
    "cmd.exe", "powershell.exe", "pwsh.exe", "cscript.exe", "wscript.exe")
Version 8 (7.13.0 release)
  • Updated query, changed from:

    event.category:process and event.type:(start or process_started) and
Version 7 (7.12.0 release)
  • Formatting only
Version 6 (7.11.2 release)
  • Formatting only
Version 5 (7.11.0 release)
  • Formatting only
Version 4 (7.10.0 release)
  • Updated query, changed from:

    event.code:1 and
Version 3 (7.9.0 release)
  • Formatting only
Version 2 (7.7.0 release)
  • Formatting only