detect_html_help_spawn_child_process.yml

name: Detect HTML Help Spawn Child Process
id: 723716de-ee55-4cd4-9759-c44e7e55ba4b
version: 11
date: '2025-05-02'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic detects the execution of hh.exe (HTML Help) spawning
  a child process, indicating the use of a Compiled HTML Help (CHM) file to execute
  Windows script code. This detection leverages data from Endpoint Detection and Response
  (EDR) agents, focusing on process creation events where hh.exe is the parent process.
  This activity is significant as it may indicate an attempt to execute malicious
  scripts via CHM files, a known technique for bypassing security controls. If confirmed
  malicious, this could lead to unauthorized code execution, potentially compromising
  the system.
data_source:
- Sysmon EventID 1
- Windows Event Log Security 4688
- CrowdStrike ProcessRollup2
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.action Processes.dest Processes.original_file_name Processes.parent_process
  Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id
  Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec
  Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level
  Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
  | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`
  | `detect_html_help_spawn_child_process_filter`'
how_to_implement: The detection is based on data that originates from Endpoint Detection
  and Response (EDR) agents. These agents are designed to provide security-related
  telemetry from the endpoints where the agent is installed. To implement this search,
  you must ingest logs that contain the process GUID, process name, and parent process.
  Additionally, you must ingest complete command-line executions. These logs must
  be processed using the appropriate Splunk Technology Add-ons that are specific to
  the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint`
  data model. Use the Splunk Common Information Model (CIM) to normalize the field
  names and speed up the data modeling process.
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/
drilldown_searches:
- name: View the detection results for - "$user$" and "$dest$"
  search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
  earliest_offset: $info_min_time$
  latest_offset: $info_max_time$
- name: View risk events for the last 7 days for - "$user$" and "$dest$"
  search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$",
    "$dest$") starthoursago=168  | stats count min(_time) as firstTime max(_time)
    as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk
    Message" values(analyticstories) as "Analytic Stories" values(annotations._all)
    as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics"
    by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
  earliest_offset: $info_min_time$
  latest_offset: $info_max_time$
rba:
  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.
  risk_objects:
  - field: user
    type: user
    score: 80
  - field: dest
    type: system
    score: 80
  threat_objects:
  - field: parent_process_name
    type: parent_process_name
  - field: process_name
    type: process_name
tags:
  analytic_story:
  - Suspicious Compiled HTML Activity
  - AgentTesla
  - Living Off The Land
  - Compromised Windows Host
  asset_type: Endpoint
  mitre_attack_id:
  - T1218.001
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  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