Potential Suspicious Change To Sensitive/Critical Files — Sigma Rule

Rule metadata and linked tags

Author: @d4ns4n_ (Wuerth-Phoenix). Source status: test; severity: medium. Source dates: 2023-05-30 / 2026-03-18.

{
  "category": "process_creation",
  "product": "linux"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 81b82185eded25b7587cd200e8014457b08b061de8ddb27e48af72de078240c0

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Potential Suspicious Change To Sensitive/Critical Files
id: 86157017-c2b1-4d4a-8c33-93b8e67e4af4
status: test
description: |
    Detects changes of sensitive and critical files. Monitors files that you don't expect to change without planning on Linux system.
    These files include, but are not limited to, system configuration files, authentication files, and critical application files.
    Attackers often target these files to maintain persistence, escalate privileges, or disrupt system operations.
references:
    - https://learn.microsoft.com/en-us/azure/defender-for-cloud/file-integrity-monitoring-overview#which-files-should-i-monitor
author: '@d4ns4n_ (Wuerth-Phoenix)'
date: 2023-05-30
modified: 2026-03-18
tags:
    - attack.impact
    - attack.t1565.001
logsource:
    category: process_creation
    product: linux
detection:
    selection_img_1:
        Image|endswith:
            - '/cat'
            - '/echo'
            - '/grep'
            - '/head'
            - '/more'
            - '/tail'
        CommandLine|contains: '>'
    selection_img_2:
        Image|endswith:
            - '/emacs'
            - '/nano'
            - '/sed'
            - '/vi'
            - '/vim'
    selection_paths:
        CommandLine|contains:
            - '/bin/login'
            - '/bin/passwd'
            - '/boot/'
            - '/etc/*.conf'
            - '/etc/cron.' # Covers different cron config files "daily", "hourly", etc.
            - '/etc/crontab'
            - '/etc/hosts'
            - '/etc/init.d'
            - '/etc/sudoers'
            - '/opt/bin/'
            - '/sbin' # Covers: '/opt/sbin', '/usr/local/sbin/', '/usr/sbin/'
            - '/usr/bin/'
            - '/usr/local/bin/'
    filter_main_mdadm.conf:
        Image|endswith: '/bin/sed'
        CommandLine|startswith:
            - 'sed -i /^*'
            - 'sed -ne s/^'
        CommandLine|endswith: '/etc/mdadm/mdadm.conf'
    condition: 1 of selection_img_* and selection_paths and not 1 of filter_main_*
falsepositives:
    - Some false positives are to be expected on user or administrator machines. Apply additional filters as needed.
level: medium

Original YAML and metadata in JSON

False positives

• Some false positives are to be expected on user or administrator machines. Apply additional filters as needed.

Source references

• https://learn.microsoft.com/en-us/azure/defender-for-cloud/file-integrity-monitoring-overview#which-files-should-i-monitor