Linux Auditd Possible Access To Credential Files

SPLUNK detection rule by Teoderick Contreras, Splunk · Apache-2.0

The following analytic detects attempts to access or dump the contents of /etc/passwd and /etc/shadow files on Linux systems. It leverages data from Linux Auditd, focusing on processes like 'cat', 'nano', 'vim', and 'vi' accessing these files. This activity is significant as it may indicate credential dumping, a technique used by adversaries to gain persistence or escalate privileges. If confirmed malicious, privileges. If confirmed malicious, attackers could obtain hashed passwords for offline cracking, leading to unauthorized access and potential system compromise.

name: Linux Auditd Possible Access To Credential Files
id: 0419cb7a-57ea-467b-974f-77c303dfe2a3
version: 13
creation_date: '2024-08-19'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic detects attempts to access or dump the contents of /etc/passwd and /etc/shadow files on Linux systems. It leverages data from Linux Auditd, focusing on processes like 'cat', 'nano', 'vim', and 'vi' accessing these files. This activity is significant as it may indicate credential dumping, a technique used by adversaries to gain persistence or escalate privileges. If confirmed malicious, privileges. If confirmed malicious, attackers could obtain hashed passwords for offline cracking, leading to unauthorized access and potential system compromise.
data_source:
    - Linux Auditd Proctitle
search: "`linux_auditd`  proctitle IN (\"*shadow*\", \"*passwd*\") AND proctitle IN (\"*cat *\", \"*nano *\", \"*vim *\", \"*vi *\")\n  | rename host as dest\n  | stats count min(_time) as firstTime max(_time) as lastTime\n    BY proctitle dest\n  | `security_content_ctime(firstTime)`\n  | `security_content_ctime(lastTime)`\n  | `linux_auditd_possible_access_to_credential_files_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. This approach enables effective monitoring and detection of linux endpoints where auditd is deployed
known_false_positives: Administrator or network operator can execute this command. Please update the filter macros to remove false positives.
references:
    - https://askubuntu.com/questions/445361/what-is-difference-between-etc-shadow-and-etc-passwd
    - https://attack.mitre.org/techniques/T1003/008/
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: A [$proctitle$] event occurred on host - [$dest$] to access or dump the contents of /etc/passwd and /etc/shadow files.
analytic_story:
    - Linux Persistence Techniques
    - Compromised Linux Host
    - China-Nexus Threat Activity
    - Salt Typhoon
    - Linux Privilege Escalation
    - Axios Supply Chain Post Compromise
asset_type: Endpoint
mitre_attack_id:
    - T1003.008
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/T1003.008/linux_auditd_access_credential/auditd_proctitle_access_cred.log
          source: auditd
          sourcetype: auditd
      test_type: unit

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Executable code, not a declarative rule

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