Suspicious CrushFTP Child Process

Status: experimental
Severity: medium
Log source: category process_creation, product windows
Author: Craig Sweeney, Matt Anderson, Jose Oregon, Tim Kasper, Faith Stratton, Samantha Shaw, Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

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.

Known false positives

Legitimate CrushFTP administrative actions
Software updates

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell `T1059.003` Command and Scripting Interpreter: Windows Command Shell

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

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

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_parent`

selection_parent:
    ParentImage|endswith: '\crushftpservice.exe'

Stage 2: `selection_child`

selection_child:
    Image|endswith:
        - '\bash.exe'
        - '\cmd.exe'
        - '\cscript.exe'
        - '\mshta.exe'
        - '\powershell.exe'
        - '\powershell_ise.exe'
        - '\pwsh.exe'
        - '\sh.exe'
        - '\wscript.exe'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\bash.exe` corpus 21 (sigma 21) `\cmd.exe` corpus 130 (sigma 130) `\cscript.exe` corpus 72 (sigma 72) `\mshta.exe` corpus 66 (sigma 66) `\powershell.exe` corpus 179 (sigma 178, kusto 1) `\powershell_ise.exe` corpus 41 (sigma 41) `\pwsh.exe` corpus 165 (sigma 164, kusto 1) `\sh.exe` corpus 16 (sigma 16) `\wscript.exe` corpus 74 (sigma 74)	`field:"Image" kind:ends_with`
`ParentImage`	ends_with	`\crushftpservice.exe`	`field:"ParentImage" kind:ends_with value:"\crushftpservice.exe"`