Detection: Linux High Frequency Of File Deletion In Boot Folder

Updated Date: 2024-11-13 ID: e27fbc5d-0445-4c4a-bc39-87f060d5c602 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects a high frequency of file deletions in the /boot/ folder on Linux systems. It leverages filesystem event logs to identify when 200 or more files are deleted within an hour by the same process. This behavior is significant as it may indicate the presence of wiper malware, such as Industroyer2, which targets critical system directories. If confirmed malicious, this activity could lead to system instability or failure, hindering the boot process and potentially causing a complete system compromise.

Search

1
2| 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 = "/boot/*" by _time span=1h  Filesystem.dest Filesystem.process_guid Filesystem.action 
3| `drop_dm_object_name(Filesystem)` 
4| where  numOfDelFilePath >= 200 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `linux_high_frequency_of_file_deletion_in_boot_folder_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 11	Linux	`'sysmon:linux'`	`'Syslog:Linux-Sysmon/Operational'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
linux_high_frequency_of_file_deletion_in_boot_folder_filter	`search *`

linux_high_frequency_of_file_deletion_in_boot_folder_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1485	Data Destruction	Impact
T1070.004	File Deletion	Defense Evasion
T1070	Indicator Removal	Defense Evasion

Actions on Objectives

Exploitation

DE.CM

CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

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

Risk Based Analytics (RBA)

Risk Message:

Multiple files detection in /boot/ folder on $dest$ by process GUID - $process_guid$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	80	No Threat Objects

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`Syslog:Linux-Sysmon/Operational`	`sysmon:linux`
Integration	✅ Passing	Dataset	`Syslog:Linux-Sysmon/Operational`	`sysmon:linux`

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: GitHub | Version: 5