Insensitive Subfolder Search Via Findstr.EXE

Status: test
Severity: low
Log source: category process_creation, product windows
Author: Furkan CALISKAN, @caliskanfurkan_, @oscd_initiative, Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

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.

Known false positives

Administrative or software activity

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution `T1564.004` Hide Artifacts: NTFS File Attributes
Credential Access	`T1552.001` Unsecured Credentials: Credentials In Files
Command & Control	`T1105` Ingress Tool Transfer

Telemetry coverage

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

Rule body

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

Stages and Predicates

Stage 0: `condition`

selection_findstr and all of selection_cli_search_*

Stage 1: `selection_findstr`

selection_findstr:
    - CommandLine|contains: findstr
    - Image|endswith: 'findstr.exe'
    - OriginalFileName: 'FINDSTR.EXE'

Stage 2: `selection_cli_search_subfolder`

selection_cli_search_subfolder:
    CommandLine|contains|windash: ' -s '

Stage 3: `selection_cli_search_insensitive`

selection_cli_search_insensitive:
    CommandLine|contains|windash: ' -i '

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`-i` transforms: `windash` corpus 4 (sigma 4) `-s` transforms: `windash` corpus 4 (sigma 3, splunk 1) `findstr` corpus 8 (sigma 6, splunk 2)	`field:"CommandLine" kind:match`
`Image`	ends_with	`findstr.exe` corpus 2 (sigma 2)	`field:"Image" kind:ends_with value:"findstr.exe"`
`OriginalFileName`	eq	`FINDSTR.EXE` corpus 12 (sigma 12)	`field:"OriginalFileName" kind:eq value:"FINDSTR.EXE"`