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title	excerpt	categories	last_modified_at	toc	toc_label	tags
Detect HTML Help Renamed	Signed Binary Proxy Execution, Compiled HTML File	Endpoint	2021-09-16	true		Signed Binary Proxy Execution Defense Evasion Compiled HTML File Defense Evasion Splunk Enterprise Splunk Enterprise Security Splunk Cloud Endpoint

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Description

The following analytic identifies a renamed instance of hh.exe (HTML Help) executing a Compiled HTML Help (CHM). 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. Validate it is the legitimate version of hh.exe by reviewing the PE metadata. hh.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64.

• Type: Hunting
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Endpoint
• Last Updated: 2021-09-16
• Author: Michael Haag, Splunk
• ID: 62fed254-513b-460e-953d-79771493a9f3

ATT&CK

ID	Technique	Tactic
T1218	Signed Binary Proxy Execution	Defense Evasion

| T1218.001 | Compiled HTML File | Defense Evasion |

Search

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_hh` by Processes.dest Processes.user Processes.parent_process_name Processes.original_file_name 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_renamed_filter`

Associated Analytic Story

• Suspicious Compiled HTML Activity

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. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Required field

• _time
• Processes.dest
• Processes.user
• Processes.parent_process_name
• Processes.parent_process
• Processes.original_file_name
• Processes.process_name
• Processes.process
• Processes.process_id
• Processes.parent_process_path
• Processes.process_path
• Processes.parent_process_id

Kill Chain Phase

• Actions on Objectives

Known False Positives

Although unlikely a renamed instance of hh.exe will be used legitimately, filter as needed.

RBA

Risk Score	Impact	Confidence	Message
80.0	80	100	The following process_name has been identified as renamed, spawning from parent_process_name.

Reference

• 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/

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.001/atomic_red_team/windows-sysmon.log

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