Detection: Rundll32 Control RunDLL World Writable Directory

Description

The following analytic detects the execution of rundll32.exe with the Control_RunDLL command, loading files from world-writable directories such as windows\temp, programdata, or appdata. This detection leverages Endpoint Detection and Response (EDR) telemetry, focusing on process command-line data and specific directory paths. This activity is significant as it may indicate an attempt to exploit CVE-2021-40444 or similar vulnerabilities, allowing attackers to execute arbitrary code. If confirmed malicious, this could lead to unauthorized code execution, 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 `process_rundll32` Processes.process=*Control_RunDLL* AND Processes.process IN ("*\\appdata\\*", "*\\windows\\temp\\*", "*\\programdata\\*") by Processes.action Processes.dest Processes.original_file_name Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `rundll32_control_rundll_world_writable_directory_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	Other	'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

CVE

• CVE-2021-40444

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

This may be tuned, or a new one related, by adding .cpl to command-line. However, it's important to look for both. Tune/filter as needed.

Associated Analytic Story

• Living Off The Land

• Microsoft MSHTML Remote Code Execution CVE-2021-40444

• Suspicious Rundll32 Activity

• Compromised Windows Host

Finding

Intermediate Findings

Threat Objects

References

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

• https://redcanary.com/blog/intelligence-insights-december-2021/

• https://strontic.github.io/xcyclopedia/library/rundll32.exe-111474C61232202B5B588D2B512CBB25.html

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444

• https://app.any.run/tasks/36c14029-9df8-439c-bba0-45f2643b0c70/

• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.002/T1218.002.yaml

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: 13