Detection: CertUtil Download With URLCache and Split Arguments

Description

The following analytic detects the use of certutil.exe to download files using the -urlcache and -split arguments. It leverages Endpoint Detection and Response (EDR) data, focusing on command-line executions that include these specific arguments. This activity is significant because certutil.exe is typically used for certificate services, and its use to download files from remote locations is uncommon and potentially malicious. If confirmed, this behavior could indicate an attempt to download and execute malicious payloads, leading to potential system compromise and unauthorized data access.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_certutil` (Processes.process=*urlcache* Processes.process=*split*) OR Processes.process=*urlcache* by Processes.dest Processes.user Processes.parent_process Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.original_file_name Processes.parent_process_id 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `certutil_download_with_urlcache_and_split_arguments_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

Limited false positives in most environments, however tune as needed based on parent-child relationship or network connection.

Associated Analytic Story

• CISA AA22-277A

• Compromised Windows Host

• DarkSide Ransomware

• Flax Typhoon

• Forest Blizzard

• Ingress Tool Transfer

• Living Off The Land

• ProxyNotShell

Risk Based Analytics (RBA)

References

• https://attack.mitre.org/techniques/T1105/

• https://www.avira.com/en/blog/certutil-abused-by-attackers-to-spread-threats

• https://web.archive.org/web/20210921110637/https://www.fireeye.com/blog/threat-research/2019/10/certutil-qualms-they-came-to-drop-fombs.html

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