Threat Huntmediumtest

Powershell Token Obfuscation - Powershell

Detects TOKEN OBFUSCATION technique from Invoke-Obfuscation in Powershell scripts. Use this rule as a threat-hunting baseline to find obfuscated scripts in your environment. Once tested and tuned, consider deploying a production detection rule based on this hunting rule.

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Open this Sigma rule in the converter with the YAML preloaded and ready for backend selection.

Launch

François HubautCreated Tue Dec 27Updated Sun Oct 19f3a98ce4-6164-4dd4-867c-4d83de7eca51windows

Hunting Hypothesis

Log Source

WindowsPowerShell Script

ProductWindows← raw: windows

CategoryPowerShell Script← raw: ps_script

Definition

Requirements: Script Block Logging must be enabled

Detection Logic

detection:
    selection:
        # Examples:
        #   IN`V`o`Ke-eXp`ResSIOn (Ne`W-ob`ject Net.WebClient).DownloadString
        #   &('In'+'voke-Expressi'+'o'+'n') (.('New-Ob'+'jec'+'t') Net.WebClient).DownloadString
        #   &("{2}{3}{0}{4}{1}"-f 'e','Expression','I','nvok','-') (&("{0}{1}{2}"-f'N','ew-O','bject') Net.WebClient).DownloadString
        - ScriptBlockText|re: '\w+`(\w+|-|.)`[\w+|\s]'
        # - ScriptBlockText|re: '\((\'(\w|-|\.)+\'\+)+\'(\w|-|\.)+\'\)' TODO: fixme
        - ScriptBlockText|re: '"(\{\d\}){2,}"\s*-f'  # trigger on at least two placeholders. One might be used for legitimate string formatting
        #   ${e`Nv:pATh}
        - ScriptBlockText|re: '(?i)\$\{`?e`?n`?v`?:`?p`?a`?t`?h`?\}'
    filter_envpath:
        ScriptBlockText|contains: '${env:path}' # TODO: Fix this. See https://github.com/SigmaHQ/sigma/pull/4964
    filter_chocolatey:
        ScriptBlockText|contains:
            - 'it will return true or false instead'  # Chocolatey install script https://github.com/chocolatey/chocolatey
            - 'The function also prevents `Get-ItemProperty` from failing' # https://docs.chocolatey.org/en-us/create/functions/get-uninstallregistrykey
    filter_exchange:
        Path|startswith: 'C:\Program Files\Microsoft\Exchange Server\'
        Path|endswith: '\bin\servicecontrol.ps1'
        ScriptBlockText|contains: '`r`n'
    condition: selection and not 1 of filter_*