Insensitive Subfolder Search Via Findstr.EXE — Sigma Rule

Rule metadata and linked tags

Author: Furkan CALISKAN, @caliskanfurkan_, @oscd_initiative, Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: low. Source dates: 2020-10-05 / 2024-03-05.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 3dd232234e34b5cc3c43ec66c6598af692577a03d80bb9f7b727a4b353eff29a

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Insensitive Subfolder Search Via Findstr.EXE
id: 04936b66-3915-43ad-a8e5-809eadfd1141
related:
    - id: bf6c39fc-e203-45b9-9538-05397c1b4f3f
      type: obsolete
status: test
description: |
    Detects execution of findstr with the "s" and "i" flags for a "subfolder" and "insensitive" search respectively. Attackers sometimes leverage this built-in utility to search the system for interesting files or filter through results of commands.
references:
    - https://lolbas-project.github.io/lolbas/Binaries/Findstr/
    - https://oddvar.moe/2018/04/11/putting-data-in-alternate-data-streams-and-how-to-execute-it-part-2/
    - https://gist.github.com/api0cradle/cdd2d0d0ec9abb686f0e89306e277b8f
author: Furkan CALISKAN, @caliskanfurkan_, @oscd_initiative, Nasreddine Bencherchali (Nextron Systems)
date: 2020-10-05
modified: 2024-03-05
tags:
    - attack.credential-access
    - attack.command-and-control
    - attack.stealth
    - attack.t1218
    - attack.t1564.004
    - attack.t1552.001
    - attack.t1105
logsource:
    category: process_creation
    product: windows
detection:
    selection_findstr:
        - CommandLine|contains: findstr
        - Image|endswith: 'findstr.exe'
        - OriginalFileName: 'FINDSTR.EXE'
    selection_cli_search_subfolder:
        CommandLine|contains|windash: ' -s '
    selection_cli_search_insensitive:
        CommandLine|contains|windash: ' -i '
    condition: selection_findstr and all of selection_cli_search_*
falsepositives:
    - Administrative or software activity
level: low

Original YAML and metadata in JSON

False positives

• Administrative or software activity

Source references

• https://lolbas-project.github.io/lolbas/Binaries/Findstr/
• https://oddvar.moe/2018/04/11/putting-data-in-alternate-data-streams-and-how-to-execute-it-part-2/
• https://gist.github.com/api0cradle/cdd2d0d0ec9abb686f0e89306e277b8f