Detection: Detect Rundll32 Application Control Bypass - syssetup

Description

The following analytic detects the execution of rundll32.exe loading syssetup.dll via the LaunchINFSection function. This method is identified through Endpoint Detection and Response (EDR) telemetry, focusing on command-line executions and process details. This activity is significant as it indicates a potential application control bypass, allowing script code execution from a file. If confirmed malicious, an attacker could execute arbitrary code, potentially leading to privilege escalation, persistence, or further network compromise. Investigate the script content, network connections, and any spawned child processes for further context.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_rundll32` Processes.process=*syssetup* 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_rundll32_application_control_bypass___syssetup_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 use syssetup.dll, triggering a false positive.

Associated Analytic Story

• Living Off The Land

• Suspicious Rundll32 Activity

Risk Based Analytics (RBA)

References

• https://attack.mitre.org/techniques/T1218/011/

• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.011/T1218.011.md

• https://lolbas-project.github.io/lolbas/Binaries/Rundll32/

• https://lolbas-project.github.io/lolbas/Libraries/Syssetup/

• https://bohops.com/2018/02/26/leveraging-inf-sct-fetch-execute-techniques-for-bypass-evasion-persistence/

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: 5