Detect HTML Help Renamed

name: Detect HTML Help Renamed
id: 62fed254-513b-460e-953d-79771493a9f3
version: 13
date: '2026-02-25'
author: Michael Haag, Splunk
status: production
type: Hunting
description: The following analytic detects instances where hh.exe (HTML Help) has been renamed and is executing a Compiled HTML Help (CHM) file. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process names and original file names. This activity is significant because attackers can use renamed hh.exe to execute malicious scripts embedded in CHM files, potentially leading to code execution. If confirmed malicious, this technique could allow attackers to run arbitrary scripts, escalate privileges, or persist within the environment, posing a significant security risk.
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.process_name!=hh.exe
        AND
        Processes.original_file_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_renamed_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 a renamed instance of hh.exe will be used legitimately, 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/
tags:
    analytic_story:
        - Suspicious Compiled HTML Activity
        - Living Off The Land
        - APT37 Rustonotto and FadeStealer
    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