Suspicious Appended Extension (via file_rename)

title: Suspicious Appended Extension (via file_rename)
id: fb38e342-4e16-5aa4-bb2d-d04184c47bb7
status: stable
description: This rule detects file renames where the target filename uses an uncommon double extension. Could indicate potential ransomware behavior renaming files and adding a custom extension to the encrypted files, such as ".jpg.crypted", ".docx.locky", etc.
references:
    - https://attack.mitre.org/techniques/T1486/
    - https://app.any.run/tasks/d66ead5a-faf4-4437-93aa-65785afaf9e5/
    - https://blog.cyble.com/2022/08/10/onyx-ransomware-renames-its-leak-site-to-vsop/
author: Huntrule Team
date: 2026-07-11
tags:
    - attack.impact
    - attack.t1486
logsource:
    product: windows
    category: file_rename
    definition: 'Requirements: Microsoft-Windows-Kernel-File Provider with at least the KERNEL_FILE_KEYWORD_RENAME_SETLINK_PATH keyword'
detection:
    selection:
        SourceFilename|endswith:
            - '.doc'
            - '.docx'
            - '.jpeg'
            - '.jpg'
            - '.lnk'
            - '.pdf'
            - '.png'
            - '.pst'
            - '.rtf'
            - '.xls'
            - '.xlsx'
        TargetFilename|contains:
            - '.doc.'
            - '.docx.'
            - '.jpeg.'
            - '.jpg.'
            - '.lnk.'
            - '.pdf.'
            - '.png.'
            - '.pst.'
            - '.rtf.'
            - '.xls.'
            - '.xlsx.'
    filter_main_generic:
        TargetFilename|endswith:
            - '.backup'
            - '.bak'
            - '.old'
            - '.orig'
            - '.temp'
            - '.tmp'
    filter_optional_anaconda:
        TargetFilename|contains: ':\ProgramData\Anaconda3\'
        TargetFilename|endswith: '.c~'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: medium