---
title: "Linux Add Files In Known Crontab Directories"
excerpt: "Cron, Scheduled Task/Job"
categories:
  - Endpoint
last_modified_at: 2021-12-17
toc: true
toc_label: ""
tags:
  - Cron
  - Execution
  - Persistence
  - Privilege Escalation
  - Scheduled Task/Job
  - Execution
  - Persistence
  - Privilege Escalation
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  - Endpoint
---



[Try in Splunk Security Cloud](https://www.splunk.com/en_us/cyber-security.html){: .btn .btn--success}

#### Description

The following analytic identifies a suspicious file creation in known cron table directories. This event is commonly abuse by malware, adversaries and red teamers to persist on the target or compromised host. crontab or cronjob is like a schedule task in windows environment where you can create an executable or script on the known crontab directories to run it base on its schedule. This Anomaly query is a good indicator to look further what file is added and who added the file if to consider it legitimate file.

- **Type**: [Anomaly](https://github.com/splunk/security_content/wiki/Detection-Analytic-Types)
- **Product**: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- **Datamodel**: [Endpoint](https://docs.splunk.com/Documentation/CIM/latest/User/Endpoint)
- **Last Updated**: 2021-12-17
- **Author**: Teoderick Contreras, Splunk
- **ID**: 023f3452-5f27-11ec-bf00-acde48001122


#### [ATT&CK](https://attack.mitre.org/)

| ID             | Technique        |  Tactic             |
| -------------- | ---------------- |-------------------- |
| [T1053.003](https://attack.mitre.org/techniques/T1053/003/) | Cron | Execution, Persistence, Privilege Escalation |

| [T1053](https://attack.mitre.org/techniques/T1053/) | Scheduled Task/Job | Execution, Persistence, Privilege Escalation |

#### 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`
```

#### Macros
The SPL above uses the following Macros:
* [security_content_ctime](https://github.com/splunk/security_content/blob/develop/macros/security_content_ctime.yml)
* [security_content_summariesonly](https://github.com/splunk/security_content/blob/develop/macros/security_content_summariesonly.yml)

Note that `linux_add_files_in_known_crontab_directories_filter` is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

#### Required field
* _time
* Filesystem.dest
* Filesystem.file_create_time
* Filesystem.file_name
* Filesystem.process_guid
* Filesystem.file_path


#### 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.

#### Associated Analytic story
* [Linux Privilege Escalation](/stories/linux_privilege_escalation)
* [Linux Persistence Techniques](/stories/linux_persistence_techniques)


#### Kill Chain Phase
* Privilege Escalation



#### RBA

| Risk Score  | Impact      | Confidence   | Message      |
| ----------- | ----------- |--------------|--------------|
| 25.0 | 50 | 50 | a file $file_name$ is created in $file_path$ on $dest$ |


Note that risk score is calculated base on the following formula: `(Impact * Confidence)/100`



#### Reference

* [https://www.sandflysecurity.com/blog/detecting-cronrat-malware-on-linux-instantly/](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/](https://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/)



#### Test Dataset
Replay any dataset to Splunk Enterprise by using our [`replay.py`](https://github.com/splunk/attack_data#using-replaypy) tool or the [UI](https://github.com/splunk/attack_data#using-ui).
Alternatively you can replay a dataset into a [Splunk Attack Range](https://github.com/splunk/attack_range#replay-dumps-into-attack-range-splunk-server)

* [https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1053.003/cronjobs_entry/sysmon_linux.log](https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1053.003/cronjobs_entry/sysmon_linux.log)



[*source*](https://github.com/splunk/security_content/tree/develop/detections/endpoint/linux_add_files_in_known_crontab_directories.yml) \| *version*: **1**