Detection: Linux High Frequency Of File Deletion In Etc Folder

Updated Date: 2024-09-30 ID: 9d867448-2aff-4d07-876c-89409a752ff8 Author: Teoderick Contreras, Splunk Type: Anomaly Product: Splunk Enterprise Security

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.

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 = "/etc/*" 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_etc_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_etc_folder_filter	`search *`

linux_high_frequency_of_file_deletion_in_etc_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

KillChainPhase.ACTIONS_ON_OBJECTIVES

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_10

APT38

LAPSUS$

Lazarus Group

Sandworm Team

APT18

APT28

APT29

APT3

APT32

APT38

APT39

APT41

APT5

Aquatic Panda

BRONZE BUTLER

Chimera

Cobalt Group

Dragonfly

Ember Bear

Evilnum

FIN10

FIN5

FIN6

FIN8

Gamaredon Group

Group5

INC Ransom

Kimsuky

Lazarus Group

Magic Hound

Metador

Mustang Panda

OilRig

Patchwork

Play

RedCurl

Rocke

Sandworm Team

Silence

TeamTNT

The White Company

Threat Group-3390

Tropic Trooper

Volt Typhoon

Wizard Spider

menuPass

APT5

Lazarus Group

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 Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

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	Risk Score	Impact	Confidence
Multiple files delted in /etc/ folder on $dest$ by process GUID - $process_guid$	49	70	70

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

https://www.sentinelone.com/labs/acidrain-a-modem-wiper-rains-down-on-europe/

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: 4