linux_obfuscated_files_or_information_base64_decode.yml

name: Linux Obfuscated Files or Information Base64 Decode
id: 303b38b2-c03f-44e2-8f41-4594606fcfc7
version: 1
date: '2022-07-27'
author: Michael Haag, Splunk
status: production
type: Anomaly
description: The following analytic identifies the use of base64 decode on Linux being
  utilized to deobfuscate a file. Identify the source of the file and determine if
  legitimate. Review parallel processes for further behavior before and after.
data_source:
- Sysmon for Linux EventID 1
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
  as lastTime from datamodel=Endpoint.Processes where Processes.process IN ("*base64
  -d*","*base64 --decode*") by Processes.dest Processes.user Processes.parent_process_name
  Processes.process_name Processes.process Processes.process_id Processes.parent_process_id
  | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`
  | `linux_obfuscated_files_or_information_base64_decode_filter`'
how_to_implement: The detection is based on data that originates from Endpoint Detection
  and Response (EDR) agents. These agents are designed to provide security-related
  telemetry from the endpoints where the agent is installed. To implement this search,
  you must ingest logs that contain the process GUID, process name, and parent process.
  Additionally, you must ingest complete command-line executions. These logs must
  be processed using the appropriate Splunk Technology Add-ons that are specific to
  the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint`
  data model. Use the Splunk Common Information Model (CIM) to normalize the field
  names and speed up the data modeling process.
known_false_positives: False positives may be present and will require some tuning
  based on processes. Filter as needed.
references:
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1027/T1027.md#atomic-test-1---decode-base64-data-into-script
- https://redcanary.com/blog/lateral-movement-with-secure-shell/
- https://linux.die.net/man/1/base64
tags:
  analytic_story:
  - Linux Living Off The Land
  asset_type: Endpoint
  confidence: 50
  impact: 30
  message: An instance of $parent_process_name$ spawning $process_name$ was identified
    on endpoint $dest$ by user $user$ decoding base64.
  mitre_attack_id:
  - T1027
  observable:
  - name: user
    type: User
    role:
    - Victim
  - name: dest
    type: Hostname
    role:
    - Victim
  - name: parent_process_name
    type: Process
    role:
    - Parent Process
  - name: process_name
    type: Process
    role:
    - Child Process
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - Processes.dest
  - Processes.user
  - Processes.parent_process_name
  - Processes.parent_process
  - Processes.original_file_name
  - Processes.process_name
  - Processes.process
  - Processes.process_id
  - Processes.parent_process_path
  - Processes.process_path
  - Processes.parent_process_id
  risk_score: 15
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1027/atomic_red_team/linux-sysmon.log
    source: Syslog:Linux-Sysmon/Operational
    sourcetype: sysmon_linux
    update_timestamp: true