RunDLL32 Spawning Explorer

Status: test
Severity: high
Log source: category process_creation, product windows
Author: elhoim, CD_ROM_
Source: github.com/SigmaHQ/sigma

Detects RunDLL32.exe spawning explorer.exe as child, which is very uncommon, often observes Gamarue spawning the explorer.exe process in an unusual way

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218.011` System Binary Proxy Execution: Rundll32

Telemetry coverage

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

Rule body

title: RunDLL32 Spawning Explorer
id: caa06de8-fdef-4c91-826a-7f9e163eef4b
status: test
description: Detects RunDLL32.exe spawning explorer.exe as child, which is very uncommon, often observes Gamarue spawning the explorer.exe process in an unusual way
references:
    - https://redcanary.com/blog/intelligence-insights-november-2021/
author: elhoim, CD_ROM_
date: 2022-04-27
modified: 2022-05-25
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\rundll32.exe'
        Image|endswith: '\explorer.exe'
    filter:
        ParentCommandLine|contains: '\shell32.dll,Control_RunDLL'
    condition: selection and not filter
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    ParentImage|endswith: '\rundll32.exe'
    Image|endswith: '\explorer.exe'

Stage 2: `not filter`

filter:
    ParentCommandLine|contains: '\shell32.dll,Control_RunDLL'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`ParentCommandLine`	match	`\shell32.dll,Control_RunDLL`	`excludes:ParentCommandLine` `field:"ParentCommandLine" value:"\shell32.dll,Control_RunDLL"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\explorer.exe` corpus 13 (sigma 13)	`field:"Image" kind:ends_with value:"\explorer.exe"`
`ParentImage`	ends_with	`\rundll32.exe` corpus 15 (sigma 15)	`field:"ParentImage" kind:ends_with value:"\rundll32.exe"`