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Description

The following analytic identifies the use of PowerShell downloading a file using DownloadString method. This particular method is utilized in many different PowerShell frameworks to download files and output to disk. Identify the source (IP/domain) and destination file and triage appropriately. If AMSI logging or PowerShell transaction logs are available, review for further details of the implant.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint- Datasource: Splunk Add-on for Sysmon
  • Last Updated: 2022-04-07
  • Author: Michael Haag, Splunk
  • ID: 4d015ef2-7adf-11eb-95da-acde48001122

Annotations

ATT&CK
ID Technique Tactic
T1059 Command and Scripting Interpreter Execution
T1059.001 PowerShell Execution
T1105 Ingress Tool Transfer Command And Control
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE
1
2
3
4
5
6
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_powershell` Processes.process=*.DownloadString*  by Processes.dest Processes.user Processes.parent_process Processes.process_name Processes.original_file_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `any_powershell_downloadstring_filter`

Macros

The SPL above uses the following Macros:

Note that any_powershell_downloadstring_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

False positives may be present and filtering will need to occur by parent process or command line argument. It may be required to modify this query to an EDR product for more granular coverage.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
56.0 80 70 An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$. This behavior identifies the use of DownloadString within PowerShell.

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