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Description

The following hunting analytic identifies renamed instances of rundll32.exe executing. rundll32.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64. During investigation, validate it is the legitimate rundll32.exe executing and what script content it is loading. This query relies on the original filename or internal name from the PE meta data. Expand the query as needed by looking for specific command line arguments outlined in other analytics.

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-04-07
  • Author: Michael Haag, Splunk
  • ID: 7360137f-abad-473e-8189-acbdaa34d114

Annotations

ATT&CK
ID Technique Tactic
T1218 Signed Binary Proxy Execution Defense Evasion
T1036 Masquerading Defense Evasion
T1218.011 Rundll32 Defense Evasion
T1036.003 Rename System Utilities Defense Evasion
Kill Chain Phase
  • Actions on Objectives
NIST
  • PR.PT
  • DE.CM
CIS20
  • CIS 8
CVE 
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| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.original_file_name=RUNDLL32.exe AND Processes.process_name!=rundll32.exe by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.original_file_name 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `suspicious_rundll32_rename_filter`

Macros

The SPL above uses the following Macros:

Note that suspicious_rundll32_rename_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
  • Processes.dest
  • Processes.user
  • Processes.parent_process_name
  • Processes.parent_process
  • Processes.original_file_name
  • Processes.process_name
  • Processes.process
  • Processes.process_id
  • Processes.parent_process_path
  • Processes.process_path
  • Processes.parent_process_id

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 node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

Although unlikely, some legitimate applications may use a moved copy of rundll32, triggering a false positive.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
63.0 70 90 Suspicious renamed rundll32.exe binary ran 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: 5