Linux Auditd Possible Append Cronjob Entry On Existing Cronjob File

Name:Linux Auditd Possible Append Cronjob Entry On Existing Cronjob File
id:fea71cf0-fa10-4ef6-9202-9682b2e0c477
version:9
date:2025-11-27
author:Teoderick Contreras, Splunk
status:production
type:Hunting
Description:The following analytic detects potential tampering with cronjob files on a Linux system. It leverages logs from Linux Auditd, focusing on events of type PATH or CWD. This activity could be significant because adversaries often use it for persistence or privilege escalation. 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 allow attackers to execute unauthorized code automatically, leading to system compromises and unauthorized data access, thereby impacting business operations and data integrity.
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/cron.*|.*/cron/.*|/etc/anacrontab.*"))
| 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_append_cronjob_entry_on_existing_cronjob_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:False positives may arise from legitimate actions by administrators or network operators who may use these commands for automation purposes. Therefore, it's recommended to adjust filter macros to eliminate such false positives.
References:
  -https://attack.mitre.org/techniques/T1053/003/
  -https://blog.aquasec.com/threat-alert-kinsing-malware-container-vulnerability
  -https://www.intezer.com/blog/research/kaiji-new-chinese-linux-malware-turning-to-golang/
drilldown_searches:
  :
tags:
  analytic_story:
    - 'XorDDos'
    - 'Linux Living Off The Land'
    - 'Compromised Linux Host'
    - 'Linux Privilege Escalation'
    - 'Scheduled Tasks'
    - 'Linux Persistence Techniques'
  asset_type:Endpoint
  mitre_attack_id:
    - 'T1053.003'
  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/T1053.003/auditd_path_cron/path_cron.log
  source: auditd
  sourcetype: auditd
manual_test:None