Detection: DLLHost with no Command Line Arguments with Network

Updated Date: 2025-06-30 ID: f1c07594-a141-11eb-8407-acde48001122 Author: Steven Dick, Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects instances of DLLHost.exe running without command line arguments while establishing a network connection. This behavior is identified using Endpoint Detection and Response (EDR) telemetry, focusing on process execution and network activity data. It is significant because DLLHost.exe typically runs with specific arguments, and its absence can indicate malicious activity, such as Cobalt Strike usage. If confirmed malicious, this activity could allow attackers to execute code, move laterally, or exfiltrate data, posing a severe threat to the network's security.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
 3as lastTime FROM datamodel=Endpoint.Processes where 
 4Processes.process_name=dllhost.exe
 5Processes.action!="blocked" 
 6by host _time span=1h 
 7Processes.action Processes.dest Processes.original_file_name
 8Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid
 9Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path
10Processes.process Processes.process_exec Processes.process_guid Processes.process_hash
11Processes.process_id Processes.process_integrity_level Processes.process_name Processes.process_path
12Processes.user Processes.user_id Processes.vendor_product
13
14| `drop_dm_object_name(Processes)` 
15
16| `security_content_ctime(firstTime)`
17
18| `security_content_ctime(lastTime)` 
19
20| regex process="(?i)(dllhost\.exe.{0,4}$)"
21
22| rename dest as src 
23
24| join host process_id [
25  
26| tstats `security_content_summariesonly`
27    count 
28    latest(All_Traffic.dest) as dest 
29    latest(All_Traffic.dest_ip) as dest_ip 
30    latest(All_Traffic.dest_port) as dest_port 
31    FROM datamodel=Network_Traffic.All_Traffic where 
32      All_Traffic.dest_port != 0 
33      by host All_Traffic.action All_Traffic.app All_Traffic.bytes All_Traffic.bytes_in 
34         All_Traffic.bytes_out All_Traffic.dest  All_Traffic.dest_ip All_Traffic.dest_port 
35         All_Traffic.dvc All_Traffic.protocol All_Traffic.protocol_version All_Traffic.src 
36         All_Traffic.src_ip All_Traffic.src_port All_Traffic.transport All_Traffic.user 
37         All_Traffic.vendor_product All_Traffic.direction All_Traffic.process_id
38  
39| `drop_dm_object_name(All_Traffic)`
40] 
41
42| `dllhost_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
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
dllhost_with_no_command_line_arguments_with_network_filter	`search *`

dllhost_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
T1055	Process Injection	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 third party applications may use a moved copy of dllhost, triggering a false positive.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The process $process_name$ was spawned by $parent_process_name$ without any command-line arguments on $src$ by $user$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
user	user	49	process_name, parent_process_name
dest	system	49	process_name, parent_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