Try in Splunk Security Cloud

Description

The following analytic identifies hh.exe (HTML Help) execution of a Compiled HTML Help (CHM) file from a remote url. 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 reputation of remote IP and domain. Some instances, it is worth decompiling the .chm file to review its original contents. hh.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64.

  • Type: TTP

  • Product: Splunk Behavioral Analytics

  • Last Updated: 2022-09-02
  • Author: Michael Haag, Splunk
  • ID: 0fec631a-7c9b-4e4c-b28b-93260953e25f

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1218.001 Compiled HTML File Defense Evasion
T1218 System Binary Proxy Execution Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17



 $main = from source  
| eval timestamp = time  
| eval metadata_uid = metadata.uid  
| eval process_pid = process.pid 
| eval process_file = process.file 
| eval process_file_path = process_file.path 
| eval process_file_name = lower(process_file.name) 
| eval process_cmd_line = process.cmd_line 
| eval actor_user = actor.user 
| eval actor_user_name = actor_user.name 
| eval actor_process = actor.process 
| eval actor_process_pid = actor_process.pid 
| eval actor_process_file = actor_process.file 
| eval actor_process_file_path = actor_process_file.path 
| eval actor_process_file_name = actor_process_file.name 
| eval device_hostname = device.hostname 
| where (process_cmd_line LIKE "%https://%" OR process_cmd_line LIKE "%http://%") AND process_file_name="hh.exe" --finding_report--

Macros

The SPL above uses the following Macros:

:information_source: windows_system_binary_proxy_execution_compiled_html_file_url_in_command_line_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • process.pid
  • process.file.path
  • process.file.name
  • process.cmd_line
  • actor.user.name
  • actor.process.pid
  • actor.process.file.path
  • actor.process.file.name
  • device.hostname

How To Implement

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

Although unlikely, some legitimate applications may retrieve a CHM remotely, filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
90.0 90 100 An instance of $process_name$ was identified on endpoint $dest_device_id$ by user $dest_user_id$ contacting a remote destination.

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

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

source | version: 4