Potential PowerShell Execution Via DLL

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Markus Neis, Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects potential PowerShell execution from a DLL instead of the usual PowerShell process as seen used in PowerShdll. This detection assumes that PowerShell commands are passed via the CommandLine.

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: Potential PowerShell Execution Via DLL
id: 6812a10b-60ea-420c-832f-dfcc33b646ba
status: test
description: |
    Detects potential PowerShell execution from a DLL instead of the usual PowerShell process as seen used in PowerShdll.
    This detection assumes that PowerShell commands are passed via the CommandLine.
references:
    - https://github.com/p3nt4/PowerShdll/blob/62cfa172fb4e1f7f4ac00ca942685baeb88ff356/README.md
author: Markus Neis, Nasreddine Bencherchali (Nextron Systems)
date: 2018-08-25
modified: 2024-03-07
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\InstallUtil.exe'
              - '\RegAsm.exe'
              - '\RegSvcs.exe'
              - '\regsvr32.exe'
              - '\rundll32.exe'
        - OriginalFileName:
              - 'InstallUtil.exe'
              - 'RegAsm.exe'
              - 'RegSvcs.exe'
              - 'REGSVR32.EXE'
              - 'RUNDLL32.EXE'
    selection_cli:
        CommandLine|contains:
            - 'Default.GetString'
            - 'DownloadString'
            - 'FromBase64String'
            - 'ICM '
            - 'IEX '
            - 'Invoke-Command'
            - 'Invoke-Expression'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith:
          - '\InstallUtil.exe'
          - '\RegAsm.exe'
          - '\RegSvcs.exe'
          - '\regsvr32.exe'
          - '\rundll32.exe'
    - OriginalFileName:
          - 'InstallUtil.exe'
          - 'RegAsm.exe'
          - 'RegSvcs.exe'
          - 'REGSVR32.EXE'
          - 'RUNDLL32.EXE'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains:
        - 'Default.GetString'
        - 'DownloadString'
        - 'FromBase64String'
        - 'ICM '
        - 'IEX '
        - 'Invoke-Command'
        - 'Invoke-Expression'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`Default.GetString` `DownloadString` corpus 9 (sigma 7, elastic 1, kusto 1) `FromBase64String` corpus 15 (sigma 9, elastic 4, splunk 2) `ICM` corpus 2 (sigma 2) `IEX` corpus 7 (sigma 6, elastic 1) `Invoke-Command` corpus 3 (sigma 2, splunk 1) `Invoke-Expression` corpus 5 (sigma 4, elastic 1)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\InstallUtil.exe` corpus 8 (sigma 8) `\RegAsm.exe` corpus 9 (sigma 9) `\RegSvcs.exe` corpus 8 (sigma 8) `\regsvr32.exe` corpus 64 (sigma 64) `\rundll32.exe` corpus 94 (sigma 94)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`InstallUtil.exe` corpus 21 (elastic 11, sigma 6, splunk 4) `REGSVR32.EXE` corpus 37 (sigma 17, elastic 15, splunk 5) `RUNDLL32.EXE` corpus 78 (sigma 35, elastic 22, splunk 21) `RegAsm.exe` corpus 14 (elastic 7, sigma 6, splunk 1) `RegSvcs.exe` corpus 13 (elastic 7, sigma 5, splunk 1)	`field:"OriginalFileName" kind:eq`