Name:Linux Add Files In Known Crontab Directories id:023f3452-5f27-11ec-bf00-acde48001122 version:4 date:2024-12-17 author:Teoderick Contreras, Splunk status:production type:Anomaly Description:The following analytic detects unauthorized file creation in known crontab directories on Unix-based systems. It leverages filesystem data to identify new files in directories such as /etc/cron* and /var/spool/cron/*. This activity is significant as it may indicate an attempt by threat actors or malware to establish persistence on a compromised host. If confirmed malicious, this could allow attackers to execute arbitrary code at scheduled intervals, potentially leading to further system compromise and unauthorized access to sensitive information. Data_source:
-Sysmon for Linux EventID 11
search:| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*/etc/cron*", "*/var/spool/cron/*") by Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.process_guid Filesystem.file_path | `drop_dm_object_name(Filesystem)` | `security_content_ctime(lastTime)` | `security_content_ctime(firstTime)` | `linux_add_files_in_known_crontab_directories_filter`
how_to_implement:To successfully implement this search, you need to be ingesting logs with the file name, file path, and process_guid executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase. known_false_positives:Administrator or network operator can create file in crontab folders for automation purposes. Please update the filter macros to remove false positives. References: -https://www.sandflysecurity.com/blog/detecting-cronrat-malware-on-linux-instantly/ -https://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/ 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:'$info_max_time$' tags: analytic_story: - 'XorDDos' - 'Linux Living Off The Land' - 'Linux Privilege Escalation' - 'Scheduled Tasks' - 'Linux Persistence Techniques' asset_type:Endpoint confidence:50 impact:50 message:a file $file_name$ is created in $file_path$ on $dest$ mitre_attack_id: - 'T1053.003' - 'T1053' observable: name:'dest' type:'Hostname' - role: - 'Victim' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' required_fields: - '_time' - 'Filesystem.dest' - 'Filesystem.file_create_time' - 'Filesystem.file_name' - 'Filesystem.process_guid' - 'Filesystem.file_path' risk_score:25 security_domain:endpoint
