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Detection rules › Sigma

Potential PowerShell Execution Policy Tampering - ProcCreation

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

Detects changes to the PowerShell execution policy registry key in order to bypass signing requirements for script execution from the CommandLine

MITRE ATT&CK coverage

TacticTechniques
Defense ImpairmentNo specific technique

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

title: Potential PowerShell Execution Policy Tampering - ProcCreation
id: cf2e938e-9a3e-4fe8-a347-411642b28a9f
related:
    - id: fad91067-08c5-4d1a-8d8c-d96a21b37814 # ProcCreation Registry
      type: similar
    - id: 87e3c4e8-a6a8-4ad9-bb4f-46e7ff99a180 # ProcCreation Cmdlet
      type: similar
    - id: 61d0475c-173f-4844-86f7-f3eebae1c66b # PowerShell ScriptBlock
      type: similar
status: test
description: Detects changes to the PowerShell execution policy registry key in order to bypass signing requirements for script execution from the CommandLine
references:
    - https://learn.microsoft.com/de-de/powershell/module/microsoft.powershell.security/set-executionpolicy?view=powershell-7.3
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-01-11
tags:
    - attack.defense-impairment
logsource:
    product: windows
    category: process_creation
detection:
    selection_path:
        CommandLine|contains:
            - '\ShellIds\Microsoft.PowerShell\ExecutionPolicy'
            - '\Policies\Microsoft\Windows\PowerShell\ExecutionPolicy'
    selection_values:
        CommandLine|contains:
            - 'Bypass'
            - 'RemoteSigned'
            - 'Unrestricted'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_path

selection_path:
    CommandLine|contains:
        - '\ShellIds\Microsoft.PowerShell\ExecutionPolicy'
        - '\Policies\Microsoft\Windows\PowerShell\ExecutionPolicy'

Stage 2: selection_values

selection_values:
    CommandLine|contains:
        - 'Bypass'
        - 'RemoteSigned'
        - 'Unrestricted'

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
  • Bypass corpus 6 (sigma 6)
  • RemoteSigned
  • Unrestricted corpus 2 (sigma 2)
  • \Policies\Microsoft\Windows\PowerShell\ExecutionPolicy
  • \ShellIds\Microsoft.PowerShell\ExecutionPolicy