CobaltStrike Load by Rundll32

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

Rundll32 can be use by Cobalt Strike with StartW function to load DLLs from the command line.

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: CobaltStrike Load by Rundll32
id: ae9c6a7c-9521-42a6-915e-5aaa8689d529
status: test
description: Rundll32 can be use by Cobalt Strike with StartW function to load DLLs from the command line.
references:
    - https://www.cobaltstrike.com/help-windows-executable
    - https://redcanary.com/threat-detection-report/
    - https://thedfirreport.com/2020/10/18/ryuk-in-5-hours/
author: Wojciech Lesicki
date: 2021-06-01
modified: 2022-09-16
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection_rundll:
        - Image|endswith: '\rundll32.exe'
        - OriginalFileName: RUNDLL32.EXE
        - CommandLine|contains:
              - 'rundll32.exe'
              - 'rundll32 '
    selection_params:
        CommandLine|contains: '.dll'
        CommandLine|endswith:
            - ' StartW'
            - ',StartW'
    condition: all of selection*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

all of selection*

Stage 1: `selection_rundll`

selection_rundll:
    - Image|endswith: '\rundll32.exe'
    - OriginalFileName: RUNDLL32.EXE
    - CommandLine|contains:
          - 'rundll32.exe'
          - 'rundll32 '

Stage 2: `selection_params`

selection_params:
    CommandLine|contains: '.dll'
    CommandLine|endswith:
        - ' StartW'
        - ',StartW'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	ends_with	`StartW` `,StartW`	`field:"CommandLine" kind:ends_with`
`CommandLine`	match	`.dll` corpus 16 (sigma 16) `rundll32` corpus 2 (sigma 2) `rundll32.exe` corpus 8 (sigma 8)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\rundll32.exe` corpus 94 (sigma 94)	`field:"Image" kind:ends_with value:"\rundll32.exe"`
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 78 (sigma 35, elastic 22, splunk 21)	`field:"OriginalFileName" kind:eq value:"RUNDLL32.EXE"`

CobaltStrike Load by Rundll32

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_rundll

Stage 2: selection_params

Indicators

Stage 0: `condition`

Stage 1: `selection_rundll`

Stage 2: `selection_params`