ConvertTo-SecureString Cmdlet Usage Via CommandLine

SIGMA detection rule by Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton · NOASSERTION

Detects usage of the "ConvertTo-SecureString" cmdlet via the commandline. Which is fairly uncommon and could indicate potential suspicious activity

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
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_powershell_cmdline_convertto_securestring/info.yml

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

a932f608-072e-4826-8e0a-6e83cf4b2457

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

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