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Description

The following analytic identifies the use of the EncodedCommand PowerShell parameter. This is typically used by Administrators to run complex scripts, but commonly used by adversaries to hide their code.
The analytic identifies all variations of EncodedCommand, as PowerShell allows the ability to shorten the parameter. For example enc, enco, encod and so forth. In addition, through our research it was identified that PowerShell will interpret different command switch types beyond the hyphen. We have added endash, emdash, horizontal bar, and forward slash.
During triage, review parallel events to determine legitimacy. Tune as needed based on admin scripts in use.
Alternatively, may use regex per matching here https://regexr.com/662ov.

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-01-18
  • Author: David Dorsey, Michael Haag, Splunk
  • ID: c4db14d9-7909-48b4-a054-aa14d89dbb19

Annotations

ATT&CK
ID Technique Tactic
T1027 Obfuscated Files or Information Defense Evasion
Kill Chain Phase
  • Command & Control
  • Actions on Objectives
NIST
  • PR.PT
  • DE.CM
  • PR.IP
CIS20
  • CIS 3
  • CIS 7
  • CIS 8
CVE
1
2
3
4
5
6
7
8
9
10
11
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_powershell` by Processes.user Processes.process_name Processes.process Processes.parent_process_name Processes.original_file_name Processes.dest Processes.process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| where match(process,"(?i)[\-
|\/
|
|
|]e(nc*o*d*e*d*c*o*m*m*a*n*d*)*\s+[^-]") 
| `malicious_powershell_process___encoded_command_filter`

Macros

The SPL above uses the following Macros:

Note that malicious_powershell_process_-_encoded_command_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.process_name
  • Processes.process
  • Processes.user
  • Processes.parent_process_name
  • Processes.dest
  • Processes.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

System administrators may use this option, but it’s not common.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
35.0 70 50 Powershell.exe running potentially malicious encodede commands on $dest$

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: 7