name: Detect HTML Help Spawn Child Process
id: 723716de-ee55-4cd4-9759-c44e7e55ba4b
version: 1
date: '2021-02-11'
author: Michael Haag, Splunk
type: batch
datamodel:
- Endpoint
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.
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
  as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name=hh.exe
  by Processes.dest Processes.user Processes.parent_process Processes.process_name
  Processes.process Processes.process_id Processes.parent_process_id | `drop_dm_object_name(Processes)`
  | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `detect_html_help_spawn_child_process_filter`'
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://cyberforensicator.com/2019/01/20/silence-dissecting-malicious-chm-files-and-performing-forensic-analysis/
tags:
  analytic_story:
  - Suspicious Compiled HTML Activity
  asset_type: Endpoint
  automated_detection_testing: passed
  cis20:
  - CIS 8
  dataset:
  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.001/atomic_red_team/windows-sysmon.log
  kill_chain_phases:
  - Actions on Objectives
  mitre_attack_id:
  - T1218.001
  nist:
  - PR.PT
  - DE.CM
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - Processes.parent_process_name
  - Processes.dest
  - Processes.user
  - Processes.parent_process
  - Processes.process_name
  - Processes.process
  - Processes.process_id
  - Processes.parent_process_id
  security_domain: endpoint
