Suspicious Binaries and Scripts in Public Folder

SIGMA detection rule by The DFIR Report · NOASSERTION

Detects the creation of a file with a suspicious extension in the public folder, which could indicate potential malicious activity.

title: Suspicious Binaries and Scripts in Public Folder
id: b447f7de-1e53-4cbf-bfb4-f1f6d0b04e4e
status: experimental
description: Detects the creation of a file with a suspicious extension in the public folder, which could indicate potential malicious activity.
references:
    - https://intel.thedfirreport.com/events/view/30032 # Private Report
    - https://intel.thedfirreport.com/eventReports/view/70 # Private Report
    - https://thedfirreport.com/2025/01/27/cobalt-strike-and-a-pair-of-socks-lead-to-lockbit-ransomware/
author: 'The DFIR Report'
date: 2025-01-23
tags:
    - attack.execution
    - attack.t1204
logsource:
    category: file_event
    product: windows
detection:
    selection:
        TargetFilename|contains: ':\Users\Public\'
        TargetFilename|endswith:
            - '.bat'
            - '.dll'
            - '.exe'
            - '.hta'
            - '.js'
            - '.ps1'
            - '.vbe'
            - '.vbs'
    condition: selection
falsepositives:
    - Administrators deploying legitimate binaries to public folders.
level: high
regression_tests_path: regression_data/rules/windows/file/file_event/file_event_win_susp_public_folder_extension/info.yml

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

a24c1767-f0bf-46c1-afee-624d94b198fd

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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