Suspicious VSFTPD Error Messages (via vsftpd)

title: Suspicious VSFTPD Error Messages (via vsftpd)
id: 748923b3-6284-55b3-9c22-efdce7427076
status: stable
description: This rule detects anomalous VSFTPD error messages that indicate a fatal or anomalous error that could be caused by exploiting attempts
references:
    - https://attack.mitre.org/techniques/T1190/
    - https://github.com/dagwieers/vsftpd/
author: Huntrule Team
date: 2026-02-17
tags:
    - attack.initial-access
    - attack.t1190
logsource:
    product: linux
    service: vsftpd
detection:
    keywords:
        - 'Connection refused: too many sessions for this address.'
        - 'Connection refused: tcp_wrappers denial.'
        - 'Bad HTTP verb.'
        - 'port and pasv both active'
        - 'pasv and port both active'
        - 'Transfer done (but failed to open directory).'
        - 'Could not set file modification time.'
        - 'bug: pid active in ptrace_sandbox_free'
        - 'PTRACE_SETOPTIONS failure'
        - 'weird status:'
        - 'couldn''t handle sandbox event'
        - 'syscall * out of bounds'
        - 'syscall not permitted:'
        - 'syscall validate failed:'
        - 'Input line too long.'
        - 'poor buffer accounting in str_netfd_alloc'
        - 'vsf_sysutil_read_loop'
    condition: keywords
falsepositives:
    - Unknown
level: medium