Linux Add Files In Known Crontab Directories
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.
- Type: Anomaly
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2024-05-15
- Author: Teoderick Contreras, Splunk
- ID: 023f3452-5f27-11ec-bf00-acde48001122
Annotations
ATT&CK
Kill Chain Phase
- Installation
- Exploitation
NIST
- DE.AE
CIS20
- CIS 10
CVE
Search
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| 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:
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 fields
List of fields required to use this analytic.
- _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
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
25.0 | 50 | 50 | a file $file_name$ is created in $file_path$ on $dest$ |
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
Reference
- 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/
Test Dataset
Replay any dataset to Splunk Enterprise by using our replay.py
tool or the UI.
Alternatively you can replay a dataset into a Splunk Attack Range
source | version: 2