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Description

This analytic is to detect a high frequency of file deletion relative to process name and process id /etc/ folder. These events was seen in acidrain wiper malware where it tries to delete all files in a non-standard directory in linux directory. This detection already contains some filter that might cause false positive during our testing. But we recommend to add more filter if needed.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-04-12
  • Author: Teoderick Contreras, Splunk
  • ID: 9d867448-2aff-4d07-876c-89409a752ff8

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1485 Data Destruction Impact
T1070.004 File Deletion Defense Evasion
T1070 Indicator Removal Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 3
  • CIS 5
  • CIS 16
CVE 


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| tstats `security_content_summariesonly` values(Filesystem.file_name) as deletedFileNames values(Filesystem.file_path) as deletedFilePath dc(Filesystem.file_path) as numOfDelFilePath count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.action=deleted Filesystem.file_path = "/etc/*" by _time span=1h  Filesystem.dest Filesystem.process_guid Filesystem.action 
| `drop_dm_object_name(Filesystem)` 
|rename process_guid as proc_guid 
|join proc_guid, _time [ 
| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.parent_process_name != unknown NOT (Processes.parent_process_name IN ("/usr/bin/dpkg", "*usr/bin/python*", "*/usr/bin/apt-*", "/bin/rm", "*splunkd", "/usr/bin/mandb")) by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest Processes.parent_process_name Processes.parent_process Processes.process_path Processes.process_guid 
| `drop_dm_object_name(Processes)` 
|rename process_guid as proc_guid 
| fields _time dest user parent_process_name parent_process process_name process_path process proc_guid registry_path registry_value_name registry_value_data registry_key_name action] 
| table  process_name process proc_guid action _time  deletedFileNames deletedFilePath numOfDelFilePath parent_process_name parent_process  process_path dest user 
| where  numOfDelFilePath >= 200 
| `linux_high_frequency_of_file_deletion_in_etc_folder_filter`

Macros

The SPL above uses the following Macros:

:information_source: linux_high_frequency_of_file_deletion_in_etc_folder_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
  • Filesystem.action
  • Processes.dest
  • Processes.user
  • Processes.parent_process_name
  • Processes.parent_process
  • Processes.process_name
  • Processes.process_path
  • Processes.process
  • Processes.process_id
  • Processes.parent_process_id

How To Implement

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase.

Known False Positives

linux package installer/uninstaller may cause this event. Please update you filter macro to remove false positives.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
49.0 70 70 a $process_name$ deleting multiple files in /etc/ folder in $dest$

:information_source: 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

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: 1