name: Detect HTML Help Spawn Child Process
id: 723716de-ee55-4cd4-9759-c44e7e55ba4b
version: 1
date: '2021-02-11'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic identifies hh.exe (HTML Help) execution of a Compiled
  HTML Help (CHM) that spawns a child process. This particular technique will load
  Windows script code from a compiled help file. CHM files may contain nearly any
  file type embedded, but only execute html/htm. Upon a successful execution, the
  following script engines may be used for execution - JScript, VBScript, VBScript.Encode,
  JScript.Encode, JScript.Compact. Analyst may identify vbscript.dll or jscript.dll
  loading into hh.exe upon execution. The "htm" and "html" file extensions were the
  only extensions observed to be supported for the execution of Shortcut commands
  or WSH script code. During investigation, identify script content origination. Review
  child process events and investigate further. hh.exe is natively found in C:\Windows\system32
  and C:\Windows\syswow64.
data_source:
- Sysmon Event ID 1
search:
  selection1:
    ParentImage: hh.exe
  condition: selection1
how_to_implement: To successfully implement this search you need to be ingesting information
  on process that include the name of the process responsible for the changes from
  your endpoints into the `Endpoint` datamodel in the `Processes` node.
known_false_positives: Although unlikely, some legitimate applications (ex. web browsers)
  may spawn a child process. Filter as needed.
references:
- https://attack.mitre.org/techniques/T1218/001/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.001/T1218.001.md
- https://lolbas-project.github.io/lolbas/Binaries/Hh/
- https://gist.github.com/mgeeky/cce31c8602a144d8f2172a73d510e0e7
- https://web.archive.org/web/20220119133748/https://cyberforensicator.com/2019/01/20/silence-dissecting-malicious-chm-files-and-performing-forensic-analysis/
tags:
  analytic_story:
  - Suspicious Compiled HTML Activity
  - Living Off The Land
  - AgentTesla
  asset_type: Endpoint
  confidence: 100
  impact: 80
  message: An instance of $parent_process_name$ spawning $process_name$ was identified
    on endpoint $dest$ by user $user$ spawning a child process, typically not normal
    behavior.
  mitre_attack_id:
  - T1218
  - T1218.001
  observable:
  - name: user
    type: User
    role:
    - Victim
  - name: dest
    type: Hostname
    role:
    - Victim
  - name: parent_process_name
    type: Process
    role:
    - Parent Process
  - name: process_name
    type: Process
    role:
    - Child Process
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  risk_score: 80
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.001/atomic_red_team/windows-sysmon.log
    source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
    sourcetype: xmlwineventlog