Detection: Suspicious Rundll32 no Command Line Arguments

Description

The following analytic detects the execution of rundll32.exe without any command line arguments. This behavior is identified using Endpoint Detection and Response (EDR) telemetry, focusing on process execution logs. It is significant because rundll32.exe typically requires command line arguments to function properly, and its absence is often associated with malicious activities, such as those performed by Cobalt Strike. If confirmed malicious, this activity could indicate an attempt to execute arbitrary code, potentially leading to credential dumping, unauthorized file writes, or other malicious actions.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6FROM datamodel=Endpoint.Processes WHERE
 7
 8`process_rundll32`
 9Processes.process IN ("*rundll32","*rundll32.exe", "*rundll32.exe\"")
10
11BY Processes.action Processes.dest Processes.original_file_name
12   Processes.parent_process Processes.parent_process_exec
13   Processes.parent_process_guid Processes.parent_process_id
14   Processes.parent_process_name Processes.parent_process_path
15   Processes.process Processes.process_exec Processes.process_guid
16   Processes.process_hash Processes.process_id Processes.process_integrity_level
17   Processes.process_name Processes.process_path Processes.user
18   Processes.user_id Processes.vendor_product
19
20
21| `drop_dm_object_name(Processes)`
22
23| `security_content_ctime(firstTime)`
24
25| `security_content_ctime(lastTime)`
26
27| `suspicious_rundll32_no_command_line_arguments_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4688	Windows	'XmlWinEventLog'	'XmlWinEventLog:Security'
Sysmon EventID 1	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
CrowdStrike ProcessRollup2	Other	'crowdstrike:events:sensor'	'crowdstrike'

Macros Used

Annotations

CVE

• CVE-2021-34527

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 a moved copy of rundll32, triggering a false positive.

Associated Analytic Story

• Graceful Wipe Out Attack

• Cobalt Strike

• Hellcat Ransomware

• PrintNightmare CVE-2021-34527

• BlackByte Ransomware

• Suspicious Rundll32 Activity

Finding

Intermediate Findings

References

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

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

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

• 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: 15