Potential Register_App.Vbs LOLScript Abuse

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: Austin Songer @austinsonger
Source: github.com/SigmaHQ/sigma

Detects potential abuse of the "register_app.vbs" script that is part of the Windows SDK. The script offers the capability to register new VSS/VDS Provider as a COM+ application. Attackers can use this to install malicious DLLs for persistence and execution.

Known false positives

Other VB scripts that leverage the same starting command line flags

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution

Telemetry coverage

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

Rule body

title: Potential Register_App.Vbs LOLScript Abuse
id: 28c8f68b-098d-45af-8d43-8089f3e35403
status: test
description: Detects potential abuse of the "register_app.vbs" script that is part of the Windows SDK. The script offers the capability to register new VSS/VDS Provider as a COM+ application. Attackers can use this to install malicious DLLs for persistence and execution.
references:
    - https://twitter.com/sblmsrsn/status/1456613494783160325?s=20
    - https://github.com/microsoft/Windows-classic-samples/blob/7cbd99ac1d2b4a0beffbaba29ea63d024ceff700/Samples/Win7Samples/winbase/vss/vsssampleprovider/register_app.vbs
author: Austin Songer @austinsonger
date: 2021-11-05
modified: 2022-07-07
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\cscript.exe'
              - '\wscript.exe'
        - OriginalFileName:
              - 'cscript.exe'
              - 'wscript.exe'
    selection_cli:
        CommandLine|contains: '.vbs -register ' # register_app.vbs
    condition: all of selection*
falsepositives:
    - Other VB scripts that leverage the same starting command line flags
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection*

Stage 1: `selection_img`

selection_img:
    - Image|endswith:
          - '\cscript.exe'
          - '\wscript.exe'
    - OriginalFileName:
          - 'cscript.exe'
          - 'wscript.exe'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains: '.vbs -register '

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`.vbs -register`	`field:"CommandLine" kind:match value:".vbs -register "`
`Image`	ends_with	`\cscript.exe` corpus 72 (sigma 72) `\wscript.exe` corpus 74 (sigma 74)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`cscript.exe` corpus 32 (sigma 17, elastic 15) `wscript.exe` corpus 38 (elastic 21, sigma 17)	`field:"OriginalFileName" kind:eq`