Potential PowerShell Execution Policy Tampering

Hunt Hypothesis

Detects changes to the PowerShell execution policy in order to bypass signing requirements for script execution

Detection Rule

Sigma (Original)

title: Potential PowerShell Execution Policy Tampering
id: fad91067-08c5-4d1a-8d8c-d96a21b37814
related:
    - id: cf2e938e-9a3e-4fe8-a347-411642b28a9f # 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 in order to bypass signing requirements for script execution
references:
    - https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.security/set-executionpolicy?view=powershell-7.3
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-01-11
modified: 2023-12-14
tags:
    - attack.defense-impairment
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|endswith:
            # Note for future readers: For PowerShell 7+ the ExecutionPolicy is handled via a setting file due to the fact that PWSH7 is available for mac and linux
            # Attackers can create a per-user setting file (powershell.config.json) and set the execution policy there
            # Learn more here: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_powershell_config?view=powershell-7.3
            - '\ShellIds\Microsoft.PowerShell\ExecutionPolicy'
            - '\Policies\Microsoft\Windows\PowerShell\ExecutionPolicy'
        Details|contains:
            - 'Bypass'
            - 'Unrestricted'
    filter_main_svchost:
        # Note: We filter out "svchost" to avoid FP with changes using "gpedit" for example.
        Image|contains:
            - ':\Windows\System32\'
            - ':\Windows\SysWOW64\'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

KQL (Azure Sentinel)

imRegistry
| where ((RegistryKey endswith "\\ShellIds\\Microsoft.PowerShell\\ExecutionPolicy" or RegistryKey endswith "\\Policies\\Microsoft\\Windows\\PowerShell\\ExecutionPolicy") and (RegistryValueData contains "Bypass" or RegistryValueData contains "Unrestricted")) and (not((ActingProcessName contains ":\\Windows\\System32\\" or ActingProcessName contains ":\\Windows\\SysWOW64\\")))

Required Data Sources

False Positive Guidance

• Unknown

References

• https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.security/set-executionpolicy?view=powershell-7.3
• SigmaHQ Rule