PowerShell Base64 Encoded Invoke Keyword

Status: test
Severity: high
Log source: category process_creation, product windows
Author: pH-T (Nextron Systems), Harjot Singh, @cyb3rjy0t
Source: github.com/SigmaHQ/sigma

Detects UTF-8 and UTF-16 Base64 encoded powershell 'Invoke-' calls

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Stealth	`T1027` Obfuscated Files or Information

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: PowerShell Base64 Encoded Invoke Keyword
id: 6385697e-9f1b-40bd-8817-f4a91f40508e
related:
    - id: fd6e2919-3936-40c9-99db-0aa922c356f7
      type: obsolete
status: test
description: Detects UTF-8 and UTF-16 Base64 encoded powershell 'Invoke-' calls
references:
    - https://thedfirreport.com/2022/05/09/seo-poisoning-a-gootloader-story/
author: pH-T (Nextron Systems), Harjot Singh, @cyb3rjy0t
date: 2022-05-20
modified: 2023-04-06
tags:
    - attack.execution
    - attack.stealth
    - attack.t1059.001
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cli_enc:
        CommandLine|contains: ' -e'
    selection_cli_invoke:
        CommandLine|contains:
            # Invoke-
            # UTF-16LE
            - 'SQBuAHYAbwBrAGUALQ'
            - 'kAbgB2AG8AawBlAC0A'
            - 'JAG4AdgBvAGsAZQAtA'
            # UTF-8
            - 'SW52b2tlL'
            - 'ludm9rZS'
            - 'JbnZva2Ut'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high
simulation:
    - type: atomic red team
      name: Create a Process using WMI Query and an Encoded Command
      technique: T1047
      atomic_guid: 7db7a7f9-9531-4840-9b30-46220135441c
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_powershell_base64_invoke/info.yml

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'

Stage 2: `selection_cli_enc`

selection_cli_enc:
    CommandLine|contains: ' -e'

Stage 3: `selection_cli_invoke`

selection_cli_invoke:
    CommandLine|contains:
        - 'SQBuAHYAbwBrAGUALQ'
        - 'kAbgB2AG8AawBlAC0A'
        - 'JAG4AdgBvAGsAZQAtA'
        - 'SW52b2tlL'
        - 'ludm9rZS'
        - 'JbnZva2Ut'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`-e` corpus 6 (sigma 5, splunk 1) `JAG4AdgBvAGsAZQAtA` `JbnZva2Ut` `SQBuAHYAbwBrAGUALQ` `SW52b2tlL` `kAbgB2AG8AawBlAC0A` `ludm9rZS`	`field:"CommandLine" kind:match`
`Image`	ends_with	`\powershell.exe` corpus 179 (sigma 178, kusto 1) `\pwsh.exe` corpus 165 (sigma 164, kusto 1)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`PowerShell.EXE` corpus 138 (sigma 84, splunk 30, elastic 24) `pwsh.dll` corpus 112 (sigma 79, splunk 30, elastic 3)	`field:"OriginalFileName" kind:eq`

PowerShell Base64 Encoded Invoke Keyword

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli_enc

Stage 3: selection_cli_invoke

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli_enc`

Stage 3: `selection_cli_invoke`