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Detection rules › Sigma

Potential Suspicious PowerShell Module File Created

Status
test
Severity
medium
Log source
product windows, category file_event
Author
Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects the creation of a new PowerShell module in the first folder of the module directory structure "\WindowsPowerShell\Modules\malware\malware.psm1". This is somewhat an uncommon practice as legitimate modules often includes a version folder.

MITRE ATT&CK coverage

TacticTechniques
PersistenceNo specific technique

Event coverage

ProviderEventTitle
SysmonEvent ID 11FileCreate

Rule body yaml

title: Potential Suspicious PowerShell Module File Created
id: e8a52bbd-bced-459f-bd93-64db45ce7657
status: test
description: Detects the creation of a new PowerShell module in the first folder of the module directory structure "\WindowsPowerShell\Modules\malware\malware.psm1". This is somewhat an uncommon practice as legitimate modules often includes a version folder.
references:
    - Internal Research
    - https://learn.microsoft.com/en-us/powershell/scripting/developer/module/understanding-a-windows-powershell-module?view=powershell-7.3
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-05-09
tags:
    - attack.persistence
logsource:
    category: file_event
    product: windows
detection:
    selection:
        TargetFilename|endswith:
            # Note: Don't include PowerShell 7 as it has default modules that don't follow this logic
            - '\\WindowsPowerShell\\Modules\\*\.ps'
            - '\\WindowsPowerShell\\Modules\\*\.dll'
    condition: selection
falsepositives:
    - False positive rate will vary depending on the environments. Additional filters might be required to make this logic usable in production.
level: medium

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    TargetFilename|endswith:
        - '\\WindowsPowerShell\\Modules\\*\.ps'
        - '\\WindowsPowerShell\\Modules\\*\.dll'

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
TargetFilenameends_with
  • \\WindowsPowerShell\\Modules\\*\.dll
  • \\WindowsPowerShell\\Modules\\*\.ps