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Description

The following analytic identifies the potential exfiltration of data using PowerShell's Invoke-RestMethod. This technique was observed in the Winter-Vivern malware, which uploads desktop screenshots and files from compromised or targeted hosts. Detecting this TTP can serve as a valuable indicator that a process is attempting to upload files to an external or internal URI link. We recommend examining the process, the files it is trying to upload, and the URL link or C2 destination where the data is being uploaded.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2023-04-05
  • Author: Teoderick Contreras, Splunk
  • ID: 06ade821-f6fa-40d0-80af-15bc1d45b3ba

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1041 Exfiltration Over C2 Channel Exfiltration
Kill Chain Phase
  • Actions On Objectives
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


1
2
3
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5



`powershell` EventCode=4104 ScriptBlockText = "*Invoke-RestMethod *" AND ScriptBlockText = "* -Uri *" AND ScriptBlockText = "* -Method *" AND ScriptBlockText = "* Post *" AND ScriptBlockText = "* -InFile *" 
| stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_exfiltration_over_c2_via_invoke_restmethod_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_exfiltration_over_c2_via_invoke_restmethod_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
  • ScriptBlockText
  • Computer
  • UserID
  • EventCode

How To Implement

To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.

Known False Positives

False positives should be limited. Filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
49.0 70 70 A PowerShell script on $Computer$ is attempting to transfer files to a remote URL.

: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

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