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Description

The following analytic identifies DLLHost.exe with no command line arguments with a network connection. It is unusual for DLLHost.exe to execute with no command line arguments present. This particular behavior is common with malicious software, including Cobalt Strike. During investigation, triage any network connections and parallel processes. Identify any suspicious module loads related to credential dumping or file writes. DLLHost.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-03-15
  • Author: Michael Haag, Splunk
  • ID: f1c07594-a141-11eb-8407-acde48001122

Annotations

ATT&CK
ID Technique Tactic
T1055 Process Injection Defense Evasion, Privilege Escalation
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE 
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| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_name=dllhost.exe by _time span=1h  Processes.process_id Processes.process_name Processes.dest Processes.process_path Processes.process Processes.parent_process_name 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| regex process="(?i)(dllhost\.exe.{0,4}$)" 
| join  process_id [
| tstats `security_content_summariesonly` count FROM datamodel=Network_Traffic.All_Traffic where All_Traffic.dest_port != 0 by All_Traffic.process_id All_Traffic.dest All_Traffic.dest_port 
| `drop_dm_object_name(All_Traffic)` 
| rename dest as C2 ] 
| table _time dest parent_process_name process_name process_path process process_id dest_port C2 
| `dllhost_with_no_command_line_arguments_with_network_filter`

Macros

The SPL above uses the following Macros:

Note that dllhost_with_no_command_line_arguments_with_network_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

  • _time
  • EventID
  • process_name
  • process_id
  • parent_process_name
  • dest_port
  • process_path

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes and port node.

Known False Positives

Although unlikely, some legitimate third party applications may use a moved copy of dllhost, triggering a false positive.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
49.0 70 70 The process $process_name$ was spawned by $parent_image$ without any command-line arguments on $dest$ by $user$.

Reference

Test Dataset

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 | version: 3