Detect HTML Help URL in Command Line

name: Detect HTML Help URL in Command Line
id: 8c5835b9-39d9-438b-817c-95f14c69a31e
version: 15
date: '2026-03-10'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic detects the execution of hh.exe (HTML Help) loading a Compiled HTML Help (CHM) file from a remote URL. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on command-line executions containing URLs. This activity is significant as it can indicate an attempt to execute malicious scripts via CHM files, potentially leading to unauthorized code execution. If confirmed malicious, this could allow an attacker to run scripts using engines like JScript or VBScript, leading to further system compromise or data exfiltration.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
    - Cisco Network Visibility Module Flow Data
search: |-
    | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Processes
      WHERE `process_hh` Processes.process=*http*
      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_url_in_command_line_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 may retrieve a CHM remotely, 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://blog.sevagas.com/?Hacking-around-HTA-files
    - 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 $user$ contacting a remote destination to potentally download a malicious payload.
    risk_objects:
        - field: user
          type: user
          score: 50
        - field: dest
          type: system
          score: 50
    threat_objects:
        - field: parent_process_name
          type: parent_process_name
        - field: process_name
          type: process_name
tags:
    analytic_story:
        - APT37 Rustonotto and FadeStealer
        - Suspicious Compiled HTML Activity
        - Living Off The Land
        - Compromised Windows Host
        - Cisco Network Visibility Module Analytics
    asset_type: Endpoint
    mitre_attack_id:
        - T1218.001
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
tests:
    - name: True Positive Test - Sysmon
      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
    - name: True Positive Test - Cisco NVM
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_network_visibility_module/cisco_nvm_flowdata/nvm_flowdata.log
          source: not_applicable
          sourcetype: cisco:nvm:flowdata