Detection: Windows SubInAcl Execution

Updated Date: 2025-01-07 ID: 12491419-1a6f-4af4-afc3-4e2052f0610e Author: Nasreddine Bencherchali, Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects the execution of the SubInAcl utility. SubInAcl is a legacy Windows Resource Kit tool from the Windows 2003 era, used to manipulate security descriptors of securable objects. It leverages data from Endpoint Detection and Response (EDR) agents, specifically searching for any process execution involving "SubInAcl.exe" binary. This activity can be significant because the utility should be rarely found on modern Windows machines, which mean any execution could potentially be considered suspicious. If confirmed malicious, this could allow an attacker to blind defenses by tampering with EventLog ACLs or modifying the access to a previously denied resource.

Search

1
2| tstats `security_content_summariesonly` values(Processes.process) as process min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where (Processes.process_name=subinacl.exe OR Processes.original_file_name=SubInAcl.exe) by Processes.dest Processes.user Processes.parent_process Processes.parent_process_name Processes.process_name Processes.original_file_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| `windows_subinacl_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

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
windows_subinacl_execution_filter	`search *`

windows_subinacl_execution_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1222.001	Windows File and Directory Permissions Modification	Defense Evasion

Exploitation

DE.AE

CIS 10

Wizard Spider

Default Configuration

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

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

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 name, and process original file name. 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

None identified. Attempts to disable security-related services should be identified and understood.

Associated Analytic Story

Defense Evasion or Unauthorized Access Via SDDL Tampering

Risk Based Analytics (RBA)

Risk Message:

An instance of $parent_process_name$ spawning $process_name$ was identified attempting to disable security services on endpoint $dest$ by user $user$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	16	process_name
user	user	16	process_name

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`

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: 2