Detection: WinRAR Spawning Shell Application

Description

The following analytic detects the execution of Windows shell processes initiated by WinRAR, such as "cmd.exe", "powershell.exe", "certutil.exe", "mshta.exe", or "bitsadmin.exe". This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process and parent process relationships. This activity is significant because it may indicate exploitation of the WinRAR CVE-2023-38831 vulnerability, where malicious scripts are executed from spoofed ZIP archives. If confirmed malicious, this could lead to unauthorized access, financial loss, and further malicious activities like data theft or ransomware attacks.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name=winrar.exe `windows_shells` OR Processes.process_name IN ("certutil.exe","mshta.exe","bitsadmin.exe") by Processes.dest Processes.user Processes.parent_process_name Processes.parent_process 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| `winrar_spawning_shell_application_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

Be aware of potential false positives - legitimate uses of WinRAR and the listed processes in your environment may cause benign activities to be flagged. Upon triage, review the destination, user, parent process, and process name involved in the flagged activity. Capture and inspect any relevant on-disk artifacts, and look for concurrent processes to identify the attack source. This approach helps analysts detect potential threats earlier and mitigate the risks.

Associated Analytic Story

• WinRAR Spoofing Attack CVE-2023-38831

Risk Based Analytics (RBA)

References

• https://www.group-ib.com/blog/cve-2023-38831-winrar-zero-day/

• https://github.com/BoredHackerBlog/winrar_CVE-2023-38831_lazy_poc

• https://github.com/b1tg/CVE-2023-38831-winrar-exploit

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