Detection: Rundll32 with no Command Line Arguments with Network

Updated Date: 2026-01-01 ID: 35307032-a12d-11eb-835f-acde48001122 Author: Steven Dick, Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the execution of rundll32.exe without command line arguments, followed by a network connection. This behavior is identified using Endpoint Detection and Response (EDR) telemetry and network traffic data. It is significant because rundll32.exe typically requires arguments to function, and its absence is often associated with malicious activity, such as Cobalt Strike. If confirmed malicious, this activity could indicate an attempt to establish unauthorized network connections, potentially leading to data exfiltration or further compromise of the system.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
 3as lastTime FROM datamodel=Endpoint.Processes where
 4`process_rundll32`
 5Processes.process IN (
 6  "*rundll32",
 7  "*rundll32.exe",
 8  "*rundll32.exe\""
 9)
10by host _time span=1h Processes.action Processes.dest Processes.original_file_name
11   Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid
12   Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path
13   Processes.process Processes.process_exec Processes.process_guid Processes.process_hash
14   Processes.process_id Processes.process_integrity_level Processes.process_name Processes.process_path
15   Processes.user Processes.user_id Processes.vendor_product
16
17| `drop_dm_object_name(Processes)`
18
19| `security_content_ctime(firstTime)`
20
21| `security_content_ctime(lastTime)`
22
23| rename dest as src
24
25| join host process_id
26[
27  
28| tstats `security_content_summariesonly` count
29  FROM datamodel=Network_Traffic.All_Traffic where
30  All_Traffic.dest_port != 0
31  by host All_Traffic.action All_Traffic.app All_Traffic.bytes All_Traffic.bytes_in All_Traffic.bytes_out
32     All_Traffic.dest  All_Traffic.dest_ip All_Traffic.dest_port All_Traffic.dvc All_Traffic.protocol
33     All_Traffic.protocol_version All_Traffic.src All_Traffic.src_ip All_Traffic.src_port
34     All_Traffic.transport All_Traffic.user All_Traffic.vendor_product All_Traffic.direction
35     All_Traffic.process_id
36  
37| `drop_dm_object_name(All_Traffic)`
38]
39
40| `rundll32_with_no_command_line_arguments_with_network_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 1	Windows	`'XmlWinEventLog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`
Sysmon EventID 3	Windows	`'XmlWinEventLog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

Name	Value
process_rundll32	`(Processes.process_name=rundll32.exe OR Processes.original_file_name=RUNDLL32.EXE)`
rundll32_with_no_command_line_arguments_with_network_filter	`search *`

rundll32_with_no_command_line_arguments_with_network_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
T1218.011	Rundll32	Defense Evasion

Exploitation

DE.CM

CIS 10

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 Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

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

Risk Based Analytics (RBA)

Risk Message:

A rundll32 process $process_name$ with no commandline argument like this process commandline $process$ in host $src$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	70	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: 13