Linux MOTD Script Added

name: Linux MOTD Script Added
id: 6dd14256-559b-4364-99d8-0968407b8074
version: 1
creation_date: '2026-07-08'
modification_date: '2026-07-08'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: |-
    The following analytic detects the creation of a file within the /etc/update-motd.d directory.
    This is used to add scripts that run with Message of the Day (MOTD) when a user logs in.
    This can be used by attackers for persistence if it contains malicious code.
data_source:
    - Sysmon for Linux EventID 11
search: |-
    | tstats `security_content_summariesonly`
      count min(_time) as firstTime
            max(_time) as lastTime

    from datamodel=Endpoint.Filesystem where

    Filesystem.file_path="/etc/update-motd.d/*"
    Filesystem.action IN ("created", "modified")

    by Filesystem.file_path Filesystem.file_name
       Filesystem.user Filesystem.dest
       Filesystem.action Filesystem.process_guid
       Filesystem.process_id

    | `drop_dm_object_name(Filesystem)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `linux_motd_script_added_filter`
how_to_implement: |-
    The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain file creation events including the file path and user context. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Filesystem` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
known_false_positives: |-
    Legitimate system administrators may add or modify MOTD scripts for valid operational purposes such as displaying system information or login banners. Filter based on known administrative activity and authorized users.
references:
    - https://github.com/Aegrah/PANIX
drilldown_searches:
    - earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
      name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: '0'
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Potential MOTD Script [$file_name$] added by [$user$] on [$dest$].
threat_objects:
    - field: file_name
      type: file_name
analytic_story:
    - Linux Persistence Techniques
    - Linux Post-Exploitation
asset_type: Endpoint
mitre_attack_id:
    - T1547
    - T1037
    - T1059.004
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      test_type: unit
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1547/linux_motd_script_added/snapattack_linux.log
          source: Syslog:Linux-Sysmon/Operational
          sourcetype: sysmon:linux