Detection: Windows Rasautou DLL Execution

Description

The following analytic detects the execution of an arbitrary DLL by the Windows Remote Auto Dialer (rasautou.exe). This behavior is identified by analyzing process creation events where rasautou.exe is executed with specific command-line arguments. This activity is significant because it leverages a Living Off The Land Binary (LOLBin) to execute potentially malicious code, bypassing traditional security controls. If confirmed malicious, this technique could allow an attacker to execute arbitrary code, potentially leading to system compromise, privilege escalation, or persistent access within the environment.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name=rasautou.exe Processes.process="* -d *"AND Processes.process="* -p *" by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.original_file_name 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `windows_rasautou_dll_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

False positives will be limited to applications that require Rasautou.exe to load a DLL from disk. Filter as needed.

Associated Analytic Story

• Windows Defense Evasion Tactics

Risk Based Analytics (RBA)

References

• https://github.com/mandiant/DueDLLigence

• https://github.com/MHaggis/notes/blob/master/utilities/Invoke-SPLDLLigence.ps1

• https://gist.github.com/NickTyrer/c6043e4b302d5424f701f15baf136513

• https://www.mandiant.com/resources/staying-hidden-on-the-endpoint-evading-detection-with-shellcode

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