Suspicious PowerShell Download - Powershell Script — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: medium. Source dates: 2017-03-05 / 2022-12-02.

{
  "product": "windows",
  "category": "ps_script",
  "definition": "Requirements: Script Block Logging must be enabled"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 3f76608f5104f323a0c50b1d5fb22434c3ae6252742059676d8777917dcef98e

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: Suspicious PowerShell Download - Powershell Script
id: 403c2cc0-7f6b-4925-9423-bfa573bed7eb
related:
    - id: 65531a81-a694-4e31-ae04-f8ba5bc33759
      type: derived
status: test
description: Detects suspicious PowerShell download command
references:
    - https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient.downloadstring?view=net-8.0
    - https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient.downloadfile?view=net-8.0
author: Florian Roth (Nextron Systems)
date: 2017-03-05
modified: 2022-12-02
tags:
    - attack.execution
    - attack.t1059.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    webclient:
        ScriptBlockText|contains: 'System.Net.WebClient'
    download:
        ScriptBlockText|contains:
            - '.DownloadFile('
            - '.DownloadFileAsync('
            - '.DownloadString('
            - '.DownloadStringAsync('
    condition: webclient and download
falsepositives:
    - PowerShell scripts that download content from the Internet
level: medium

Original YAML and metadata in JSON

False positives

• PowerShell scripts that download content from the Internet

Source references

• https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient.downloadstring?view=net-8.0
• https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient.downloadfile?view=net-8.0