splunk_escuAnomaly

Linux Auditd Nopasswd Entry In Sudoers File

The following analytic detects the addition of NOPASSWD entries to the /etc/sudoers file on Linux systems. It leverages Linux Auditd data to identify command lines containing "NOPASSWD:". This activity is significant because it allows users to execute commands with elevated privileges without requiring a password, which can be exploited by adversaries to maintain persistent, privileged access. If confirmed malicious, this could lead to unauthorized privilege escalation, persistent access, and potential compromise of sensitive data and system integrity.

MITRE ATT&CK

T1548.003

privilege-escalationdefense-evasion

Detection Query

`linux_auditd` proctitle = "*NOPASSWD*"
  | rename host as dest
  | stats count min(_time) as firstTime max(_time) as lastTime
    BY proctitle dest
  | `security_content_ctime(firstTime)`
  | `security_content_ctime(lastTime)`
  | `linux_auditd_nopasswd_entry_in_sudoers_file_filter`

Author

Teoderick Contreras, Splunk

Created

2026-03-10

Data Sources

Linux Auditd Proctitle

References

Tags

Linux Persistence TechniquesCompromised Linux HostChina-Nexus Threat ActivitySalt TyphoonLinux Privilege Escalation

Raw Content

name: Linux Auditd Nopasswd Entry In Sudoers File
id: 651df959-ad17-4b73-a323-90cb96d5fa1b
version: 10
date: '2026-03-10'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic detects the addition of NOPASSWD entries to the /etc/sudoers file on Linux systems. It leverages Linux Auditd data to identify command lines containing "NOPASSWD:". This activity is significant because it allows users to execute commands with elevated privileges without requiring a password, which can be exploited by adversaries to maintain persistent, privileged access. If confirmed malicious, this could lead to unauthorized privilege escalation, persistent access, and potential compromise of sensitive data and system integrity.
data_source:
    - Linux Auditd Proctitle
search: |-
    `linux_auditd` proctitle = "*NOPASSWD*"
      | rename host as dest
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY proctitle dest
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `linux_auditd_nopasswd_entry_in_sudoers_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. 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/334318/sudoers-file-enable-nopasswd-for-user-all-commands
    - https://help.ubuntu.com/community/Sudoers
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 ("$dest$") starthoursago=168  | 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: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: A [$proctitle$] event occurred on host - [$dest$] to add NOPASSWD entry in sudoers file.
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects: []
tags:
    analytic_story:
        - Linux Persistence Techniques
        - Compromised Linux Host
        - China-Nexus Threat Activity
        - Salt Typhoon
        - Linux Privilege Escalation
    asset_type: Endpoint
    mitre_attack_id:
        - T1548.003
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1548.003/linux_auditd_nopasswd/linux_auditd_nopasswd2.log
          source: auditd
          sourcetype: auditd