name: Linux Decode Base64 to Shell
id: 637b603e-1799-40fd-bf87-47ecbd551b66
version: 1
date: '2022-07-27'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic identifies base64 being decoded and passed to
  a Linux shell.
data_source:
- Sysmon Event ID 1
search:
  selection1:
    CommandLine: '*|*'
  selection2:
    CommandLine:
    - '*base64 -d*'
    - '*base64 --decode*'
  condition: selection1 and selection2
how_to_implement: To successfully implement this search you need to be ingesting information
  on process that include the name of the process responsible for the changes from
  your endpoints into the `Endpoint` datamodel in the `Processes` node. In addition,
  confirm the latest CIM App 4.20 or higher is installed and the latest TA for the
  endpoint product.
known_false_positives: False positives may be present based on legitimate software
  being utilized. 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: 50
  message: An instance of $parent_process_name$ spawning $process_name$ was identified
    on endpoint $dest$ by user $user$ decoding base64 and passing it to a shell.
  mitre_attack_id:
  - T1027
  - T1059.004
  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
  risk_score: 25
  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