Suspicious ConvertTo-SecureString Cmdlet Use Through CommandLine (via process_creation)

title: Suspicious ConvertTo-SecureString Cmdlet Use Through CommandLine (via process_creation)
id: f5fdb880-1822-5c69-9bdd-80a7c41e4f64
status: stable
description: This rule detects use of the "ConvertTo-SecureString" cmdlet via the commandline. Which is fairly uncommon and could indicate potential anomalous behavior
references:
    - https://attack.mitre.org/techniques/T1059/001/
    - https://attack.mitre.org/techniques/T1027/
    - 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: Huntrule Team
date: 2026-04-10
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:
    - Unknown
level: medium