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Description

The following analytic detects suspicious PowerShell script execution involving the cryptography namespace via EventCode 4104. It leverages PowerShell Script Block Logging to identify scripts using cryptographic functions, excluding common hashes like SHA and MD5. This activity is significant as it is often associated with malware that decrypts or decodes additional malicious payloads. If confirmed malicious, this could allow an attacker to execute further code, escalate privileges, or establish persistence within the environment. Analysts should investigate the parent process, decrypted data, network connections, and the user executing the script.

  • Type: Anomaly

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

  • Last Updated: 2024-05-27
  • Author: Teoderick Contreras, Splunk
  • ID: f8b482f4-6d62-49fa-a905-dfa15698317b

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1059.001 PowerShell Execution
T1059 Command and Scripting Interpreter Execution
Kill Chain Phase
  • Installation
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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`powershell` EventCode=4104 ScriptBlockText = "*System.Security.Cryptography*" AND NOT(ScriptBlockText IN ("*SHA*", "*MD5*", "*DeriveBytes*")) 
| stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID 
| rename Computer as dest 
| rename UserID as user 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_powershell_cryptography_namespace_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_powershell_cryptography_namespace_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
  • Opcode
  • Computer
  • UserID
  • EventCodes

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
25.0 50 50 A suspicious powershell script contains cryptography command detected on host $dest$

: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: 3