PowerShell Base64 Encoded IEX Cmdlet — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2019-08-23 / 2023-04-06.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 7d2d5e96ae03d6a5798f5bc3fa80190849826288a2f32ced56cea7cb31ea62fe

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: PowerShell Base64 Encoded IEX Cmdlet
id: 88f680b8-070e-402c-ae11-d2914f2257f1
status: test
description: Detects usage of a base64 encoded "IEX" cmdlet in a process command line
references:
    - Internal Research
author: Florian Roth (Nextron Systems)
date: 2019-08-23
modified: 2023-04-06
tags:
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - CommandLine|base64offset|contains:
              - 'IEX (['
              - 'iex (['
              - 'iex (New'
              - 'IEX (New'
              - 'IEX(['
              - 'iex(['
              - 'iex(New'
              - 'IEX(New'
              - "IEX(('"
              - "iex(('"
        # UTF16 LE
        - CommandLine|contains:
              - 'SQBFAFgAIAAoAFsA'
              - 'kARQBYACAAKABbA'
              - 'JAEUAWAAgACgAWw'
              - 'aQBlAHgAIAAoAFsA'
              - 'kAZQB4ACAAKABbA'
              - 'pAGUAeAAgACgAWw'
              - 'aQBlAHgAIAAoAE4AZQB3A'
              - 'kAZQB4ACAAKABOAGUAdw'
              - 'pAGUAeAAgACgATgBlAHcA'
              - 'SQBFAFgAIAAoAE4AZQB3A'
              - 'kARQBYACAAKABOAGUAdw'
              - 'JAEUAWAAgACgATgBlAHcA'
    condition: selection
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• Internal Research (source note; no public URL supplied)