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Detection rules › Sigma

ConvertTo-SecureString Cmdlet Usage Via CommandLine

Status
test
Severity
medium
Log source
product windows, category process_creation
Author
Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton
Source
github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059.001 Command and Scripting Interpreter: PowerShell
StealthT1027 Obfuscated Files or Information

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

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

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_img

selection_img:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'

Stage 2: selection_cli

selection_cli:
    CommandLine|contains: 'ConvertTo-SecureString'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
CommandLinematch
  • ConvertTo-SecureString corpus 2 (sigma 1, chronicle 1)
Imageends_with
  • \powershell.exe corpus 182 (sigma 182)
  • \pwsh.exe corpus 168 (sigma 168)
OriginalFileNameeq
  • PowerShell.EXE corpus 120 (sigma 84, splunk 30, elastic 6)
  • pwsh.dll corpus 112 (sigma 79, splunk 30, elastic 3)