Detection: Detect Rundll32 Inline HTA Execution

Description

The following analytic detects the execution of "rundll32.exe" with inline protocol handlers such as "JavaScript", "VBScript", and "About". This behavior is identified using Endpoint Detection and Response (EDR) telemetry, focusing on command-line arguments. This activity is significant as it is often associated with fileless malware or application whitelisting bypass techniques. If confirmed malicious, this could allow an attacker to execute arbitrary code, bypass security controls, and maintain persistence within the environment.

Search

1
2| tstats `security_content_summariesonly` count values(Processes.process) as process values(Processes.parent_process) as parent_process min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_rundll32` (Processes.process=*vbscript* OR Processes.process=*javascript* OR Processes.process=*about*) by Processes.user Processes.process_name Processes.parent_process_name Processes.original_file_name Processes.dest  
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)` 
6| `detect_rundll32_inline_hta_execution_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, some legitimate applications may exhibit this behavior, triggering a false positive.

Associated Analytic Story

• Living Off The Land

• NOBELIUM Group

• Suspicious MSHTA Activity

Risk Based Analytics (RBA)

References

• https://github.com/redcanaryco/AtomicTestHarnesses

• https://redcanary.com/blog/introducing-atomictestharnesses/

• https://docs.microsoft.com/en-us/windows/win32/search/-search-3x-wds-extidx-prot-implementing

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: 4