Linux Auditd Possible Access Or Modification Of Sshd Config File

name: Linux Auditd Possible Access Or Modification Of Sshd Config File
id: acb3ea33-70f7-47aa-b335-643b3aebcb2f
version: 11
creation_date: '2022-01-12'
modification_date: '2026-05-13'
author: Teoderick Contreras, Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: |
    The following analytic detects access, deletion or modification of the ssh_config file on Linux systems.
    It leverages data from Linux Auditd, focusing on events of type PATH with a nametype of ("NORMAL", "CREATE", "DELETE").
    This activity could be significant because unauthorized changes to ssh_config can allow threat actors to redirect port connections or use unauthorized keys, potentially compromising the system.
    Correlate this with related EXECVE or PROCTITLE events to identify the process or user responsible for the access or modification.
    If confirmed malicious, this could lead to unauthorized access, privilege escalation, or persistent backdoor access, posing a severe security risk.
data_source:
    - Linux Auditd Path
    - Linux Auditd Cwd
search: |
    `linux_auditd`
    (
      (type=PATH nametype IN ("NORMAL", "CREATE", "DELETE"))
      OR
      type=CWD
    )
    | rex "msg=audit\([^)]*:(?<audit_id>\d+)\)"

    | stats
      values(type) as types
      values(name) as names
      values(nametype) as nametype
      values(cwd) as cwd_list
      values(_time) as event_times
      by audit_id, host

    | eval current_working_directory = coalesce(mvindex(cwd_list, 0), "N/A")
    | eval candidate_paths = mvmap(names, if(match(names, "^/"), names, current_working_directory + "/" + names))
    | eval matched_paths = mvfilter(match(candidate_paths, "/etc/ssh/ssh_config.*"))
    | eval match_count = mvcount(matched_paths)
    | eval reconstructed_path = mvindex(matched_paths, 0)
    | eval e_time = mvindex(event_times, 0)
    | where match_count > 0
    | rename host as dest

    | stats count min(e_time) as firstTime max(e_time) as lastTime
      values(nametype) as nametype
      by current_working_directory
         reconstructed_path
         match_count
         dest
         audit_id

    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    |  `linux_auditd_possible_access_or_modification_of_sshd_config_file_filter`
how_to_implement: |
    To implement this detection, the process begins by ingesting auditd
    data, that consist SYSCALL, TYPE, EXECVE and PROCTITLE events, which captures command-line
    executions and process details on Unix/Linux systems. These logs should be ingested
    and processed using Splunk Add-on for Unix and Linux (https://splunkbase.splunk.com/app/833),
    which is essential for correctly parsing and categorizing the data. The next step
    involves normalizing the field names  to match the field names set by the Splunk
    Common Information Model (CIM) to ensure consistency across different data sources
    and enhance the efficiency of data modeling and make sure the type=CWD record type is activate in your auditd configuration.
    This approach enables effective monitoring and detection of linux endpoints where auditd is deployed.
known_false_positives: |
    Administrator or network operator can use this commandline for automation purposes.
    Please update the filter macros to remove false positives.
references:
    - https://www.hackingarticles.in/ssh-penetration-testing-port-22/
    - https://attack.mitre.org/techniques/T1098/004/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | 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: $reconstructed_path$ has been accessed with type $nametype$ on host - [$dest$]
analytic_story:
    - Linux Living Off The Land
    - Linux Privilege Escalation
    - Linux Persistence Techniques
    - Compromised Linux Host
asset_type: Endpoint
mitre_attack_id:
    - T1098.004
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1098.004/auditd_path_ssh_config/path_ssh_config.log
          source: auditd
          sourcetype: auditd
      test_type: unit