Process Activity via Compiled HTML File

edit

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-endpoint.events.*
  • 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

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Execution

Version: 10 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 7.16.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

edit

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.

Rule query

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

Threat mapping

edit

Framework: MITRE ATT&CKTM

Rule version history

edit
Version 10 (7.16.0 release)
  • Updated query, changed from:

    process where event.type in ("start", "process_started") and
    process.parent.name : "hh.exe" and process.name : ("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
    process.name:hh.exe
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 process.name:hh.exe
Version 3 (7.9.0 release)
  • Formatting only
Version 2 (7.7.0 release)
  • Formatting only