Powershell Token Obfuscation - Powershell

 1title: Powershell Token Obfuscation - Powershell
 2id: f3a98ce4-6164-4dd4-867c-4d83de7eca51
 3related:
 4    - id: deb9b646-a508-44ee-b7c9-d8965921c6b6
 5      type: similar
 6status: test
 7description: Detects TOKEN OBFUSCATION technique from Invoke-Obfuscation
 8references:
 9    - https://github.com/danielbohannon/Invoke-Obfuscation
10author: frack113
11date: 2022-12-27
12modified: 2023-03-24
13tags:
14    - attack.defense-evasion
15    - attack.t1027.009
16logsource:
17    product: windows
18    category: ps_script
19    definition: 'Requirements: Script Block Logging must be enabled'
20detection:
21    selection:
22        # Examples:
23        #   IN`V`o`Ke-eXp`ResSIOn (Ne`W-ob`ject Net.WebClient).DownloadString
24        #   &('In'+'voke-Expressi'+'o'+'n') (.('New-Ob'+'jec'+'t') Net.WebClient).DownloadString
25        #   &("{2}{3}{0}{4}{1}"-f 'e','Expression','I','nvok','-') (&("{0}{1}{2}"-f'N','ew-O','bject') Net.WebClient).DownloadString
26        - ScriptBlockText|re: '\w+`(\w+|-|.)`[\w+|\s]'
27        # - ScriptBlockText|re: '\((\'(\w|-|\.)+\'\+)+\'(\w|-|\.)+\'\)' TODO: fixme
28        - ScriptBlockText|re: '"(\{\d\}){2,}"\s*-f'  # trigger on at least two placeholders. One might be used for legitimate string formatting
29        #   ${e`Nv:pATh}
30        - ScriptBlockText|re: '(?i)\$\{`?e`?n`?v`?:`?p`?a`?t`?h`?\}'
31    filter_envpath:
32        ScriptBlockText|contains: '${env:path}' # TODO: Fix this. See https://github.com/SigmaHQ/sigma/pull/4964
33    filter_chocolatey:
34        ScriptBlockText|contains:
35            - 'it will return true or false instead'  # Chocolatey install script https://github.com/chocolatey/chocolatey
36            - 'The function also prevents `Get-ItemProperty` from failing' # https://docs.chocolatey.org/en-us/create/functions/get-uninstallregistrykey
37    filter_exchange:
38        Path|startswith: 'C:\Program Files\Microsoft\Exchange Server\'
39        Path|endswith: '\bin\servicecontrol.ps1'
40        ScriptBlockText|contains: '`r`n'
41    condition: selection and not 1 of filter_*
42falsepositives:
43    - Unknown
44level: high