Invoke-Obfuscation Via Use Rundll32 - PowerShell

Status: test
Severity: high
Log source: category ps_script, product windows
Author: Nikita Nazarov, oscd.community
Source: github.com/SigmaHQ/sigma

Detects Obfuscated Powershell via use Rundll32 in Scripts

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
PowerShell	Event ID 4104: Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body

title: Invoke-Obfuscation Via Use Rundll32 - PowerShell
id: a5a30a6e-75ca-4233-8b8c-42e0f2037d3b
status: test
description: Detects Obfuscated Powershell via use Rundll32 in Scripts
references:
    - https://github.com/SigmaHQ/sigma/issues/1009
author: Nikita Nazarov, oscd.community
date: 2019-10-08
modified: 2022-11-29
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection_4104:
        ScriptBlockText|contains|all:
            - '&&'
            - 'rundll32'
            - 'shell32.dll'
            - 'shellexec_rundll'
        ScriptBlockText|contains:
            - 'value'
            - 'invoke'
            - 'comspec'
            - 'iex'
    condition: selection_4104
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection_4104

Stage 1: `selection_4104`

selection_4104:
    ScriptBlockText|contains|all:
        - '&&'
        - 'rundll32'
        - 'shell32.dll'
        - 'shellexec_rundll'
    ScriptBlockText|contains:
        - 'value'
        - 'invoke'
        - 'comspec'
        - 'iex'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ScriptBlockText`	match	`&&` corpus 2 (sigma 2) `comspec` `iex` corpus 2 (sigma 2) `invoke` `rundll32` corpus 2 (sigma 2) `shell32.dll` corpus 2 (sigma 2) `shellexec_rundll` corpus 2 (sigma 2) `value`	`field:"ScriptBlockText" kind:match`

Invoke-Obfuscation Via Use Rundll32 - PowerShell

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_4104

Indicators

Stage 0: `condition`

Stage 1: `selection_4104`