ConvertTo-SecureString Cmdlet Usage Via CommandLine — Sigma Rule

Rule metadata and linked tags

Author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton. Source status: test; severity: medium. Source dates: 2020-10-11 / 2023-02-01.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 27ee1982cf02e37a85fd0bb1680d6033d4c1b43f1872f08bebb039ba9645846a

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: ConvertTo-SecureString Cmdlet Usage Via CommandLine
id: 74403157-20f5-415d-89a7-c505779585cf
status: test
description: Detects usage of the "ConvertTo-SecureString" cmdlet via the commandline. Which is fairly uncommon and could indicate potential suspicious activity
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=65
    - https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.security/convertto-securestring?view=powershell-7.3#examples
author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton
date: 2020-10-11
modified: 2023-02-01
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cli:
        CommandLine|contains: 'ConvertTo-SecureString'
    condition: all of selection_*
falsepositives:
    - Legitimate use to pass password to different powershell commands
level: medium

Original YAML and metadata in JSON

False positives

• Legitimate use to pass password to different powershell commands

Source references

• https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=65
• https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.security/convertto-securestring?view=powershell-7.3#examples