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Description

The following analytic detects a high frequency of file deletions in the /etc/ folder on Linux systems. It leverages the Endpoint.Filesystem data model to identify instances where 200 or more files are deleted within an hour, grouped by process name and process ID. This behavior is significant as it may indicate the presence of wiper malware, such as AcidRain, which aims to delete critical system files. If confirmed malicious, this activity could lead to severe system instability, data loss, and potential disruption of services.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2024-05-10
  • 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
  • Actions On Objectives
  • Exploitation
NIST
  • DE.AE
CIS20
  • CIS 10
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)`  
| where  numOfDelFilePath >= 200 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `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

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 Multiple files delted in /etc/ folder on $dest$ by process GUID - $process_guid$

: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: 3