Techniques
Sample rules
Linux Possible Append Cronjob Entry on Existing Cronjob File
- source: splunk
- technicques:
- T1053.003
- T1053
Description
The following analytic is designed to detect potential tampering with cronjob files on a Linux system. It specifically searches for command lines that may be used to append code to existing cronjob files, a technique often employed by adversaries, malware, and red teamers for persistence or privilege escalation. Altering existing or sometimes normal cronjob script files allows malicious code to be executed automatically. The analytic operates by monitoring logs for specific process names, parent processes, and command-line executions from your endpoints. It specifically checks for any ’echo’ command which modifies files in directories commonly associated with cron jobs such as ‘/etc/cron*’, ‘/var/spool/cron/’, and ‘/etc/anacrontab’. If such activity is detected, an alert is triggered. This behavior is worth identifying for a SOC because malicious cron jobs can lead to system compromises and unauthorized data access, impacting business operations and data integrity.
Detection logic
| tstats `security_content_summariesonly` count from datamodel=Endpoint.Processes where Processes.process = "*echo*" AND Processes.process IN("*/etc/cron*", "*/var/spool/cron/*", "*/etc/anacrontab*") by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.process_guid
| `drop_dm_object_name(Processes)`
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `linux_possible_append_cronjob_entry_on_existing_cronjob_file_filter`