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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

ATT&CK

ID Technique Tactic
T1027 Obfuscated Files or Information Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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| 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:

:information_source: 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 fields

List of fields required to use this analytic.

  • _time
  • Processes.process_name
  • Processes.process
  • Processes.user
  • Processes.parent_process_name
  • Processes.dest
  • Processes.process_id

How To Implement

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

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 $dest$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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