Linux Auditd Unix Shell Configuration Modification

name: Linux Auditd Unix Shell Configuration Modification
id: 66f737c6-3f7f-46ed-8e9b-cc0e5bf01f04
version: 11
creation_date: '2024-08-22'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: TTP
description: |
    The following analytic detects suspicious access or modifications to Unix shell configuration files, which may indicate an attempt to alter system behavior or gain unauthorized access.
    Unix shell configuration files, such as `.bashrc` or `.profile`, control user environment settings and command execution.
    Unauthorized changes to these files can be used to execute malicious commands, escalate privileges, or hide malicious activities.
    By monitoring for unusual or unauthorized modifications to shell configuration files, this analytic helps identify potential security threats, allowing security teams to respond quickly and mitigate risks.
    Correlate this with related EXECVE or PROCTITLE events to identify the process or user responsible for the access or modification.
data_source:
    - Linux Auditd Path
    - Linux Auditd Cwd
search: |
    `linux_auditd`
    (type=PATH 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/profile|/etc/shells|/etc/profile\\.d/.*|/etc/bash\\.bashrc.*|/etc/bashrc|.*/zsh/zprofile|.*/zsh/zshrc|.*/zsh/zlogin|.*/zsh/zlogout|/etc/csh\\.cshrc.*|/etc/csh\\.login.*|/root/\\.bashrc.*|/root/\\.bash_profile.*|/root/\\.profile.*|/root/\\.zshrc.*|/root/\\.zprofile.*|/home/.*/\\.bashrc.*|/home/.*/\\.zshrc.*|/home/.*/\\.bash_profile.*|/home/.*/\\.zprofile.*|/home/.*/\\.profile.*|/home/.*/\\.bash_login.*|/home/.*/\\.bash_logout.*|/home/.*/\\.zlogin.*|/home/.*/\\.zlogout.*"))
    | 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_unix_shell_configuration_modification_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 application for automation purposes.
    Please update the filter macros to remove false positives.
references:
    - https://www.splunk.com/en_us/blog/security/deep-dive-on-persistence-privilege-escalation-technique-and-detection-in-linux-platform.html
    - https://github.com/peass-ng/PEASS-ng/tree/master/linPEAS
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"
finding:
    title: A [$nametype$] event occurred on host - [$dest$] to modify the unix shell configuration file.
    entity:
        field: dest
        type: system
        score: 50
analytic_story:
    - Linux Living Off The Land
    - Linux Privilege Escalation
    - Linux Persistence Techniques
    - Compromised Linux Host
    - QuietVault
asset_type: Endpoint
mitre_attack_id:
    - T1546.004
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/T1546.004/linux_auditd_unix_shell_mod_config/linux_path_profile_d.log
          source: auditd
          sourcetype: auditd
      test_type: unit