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Suspicious CrushFTP Child Process

SIGMA detection rule by Craig Sweeney, Matt Anderson, Jose Oregon, Tim Kasper, Faith Stratton, Samantha Shaw, Swachchhanda Shrawan Poudel (Nextron Systems) · NOASSERTION

Detects suspicious child processes spawned by the CrushFTP service that may indicate exploitation of remote code execution vulnerabilities such as CVE-2025-31161, where attackers can achieve RCE through crafted HTTP requests. The detection focuses on commonly abused Windows executables (like powershell.exe, cmd.exe etc.) that attackers typically use post-exploitation to execute malicious commands.

title: Suspicious CrushFTP Child Process
id: 459628e3-1b00-4e9b-9e5b-7da8961aea35
status: experimental
description: |
    Detects suspicious child processes spawned by the CrushFTP service that may indicate exploitation of remote code execution vulnerabilities such as
    CVE-2025-31161, where attackers can achieve RCE through crafted HTTP requests.
    The detection focuses on commonly abused Windows executables (like powershell.exe, cmd.exe etc.) that attackers typically use post-exploitation to execute malicious commands.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-2825
    - https://www.crushftp.com/crush11wiki/Wiki.jsp?page=Update
    - https://outpost24.com/blog/crushftp-auth-bypass-vulnerability/
    - https://attackerkb.com/topics/k0EgiL9Psz/cve-2025-2825/rapid7-analysis
    - https://projectdiscovery.io/blog/crushftp-authentication-bypass
author: Craig Sweeney, Matt Anderson, Jose Oregon, Tim Kasper, Faith Stratton, Samantha Shaw, Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-04-10
tags:
    - attack.initial-access
    - attack.execution
    - attack.t1059.001
    - attack.t1059.003
    - attack.t1190
    - cve.2025-31161
    - detection.emerging-threats
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent:
        ParentImage|endswith: '\crushftpservice.exe'
    selection_child:
        Image|endswith:
            - '\bash.exe'
            - '\cmd.exe'
            - '\cscript.exe'
            - '\mshta.exe'
            - '\powershell.exe'
            - '\powershell_ise.exe'
            - '\pwsh.exe'
            - '\sh.exe'
            - '\wscript.exe'
    condition: all of selection_*
falsepositives:
    - Legitimate CrushFTP administrative actions
    - Software updates
level: medium

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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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