Detection: Detect HTML Help Renamed

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.

Search

1
2| 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.dest Processes.user Processes.parent_process_name Processes.original_file_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `detect_html_help_renamed_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	N/A	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Windows Event Log Security 4688	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

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.

Associated Analytic Story

• Living Off The Land

• Suspicious Compiled HTML Activity

Risk Based Analytics (RBA)

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/

Detection Testing

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: GitHub | Version: 7