name: Linux SSH Authorized Keys Modification
id: f5ab595e-28e5-4327-8077-5008ba97c850
version: 1
date: '2022-07-27'
author: Michael Haag, Splunk
type: Anomaly
datamodel:
- Endpoint
description: The following analytic identifies based on process execution the modification of SSH Authorized Keys. Adversaries perform this behavior to persist on endpoints.
  During triage, review parallel processes and capture any additional file modifications for review. 
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
  as lastTime from datamodel=Endpoint.Processes where  Processes.process_name IN ("bash","cat") Processes.process IN ("*/authorized_keys*")
   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_ssh_authorized_keys_modification_filter`'
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: Filtering will be required as system administrators will add and remove. One way to filter query is to add "echo".
references:
  - https://redcanary.com/blog/lateral-movement-with-secure-shell/
  - https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1098.004/T1098.004.md
tags:
  analytic_story:
  - Linux Living Off The Land
  asset_type: Endpoint
  cis20:
  - CIS 3
  - CIS 5
  - CIS 16
  confidence: 50
  context:
  - Source:Endpoint
  - Stage:Persistence
  dataset:
  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1098.004/ssh_authorized_keys/authkey_linux-sysmon.log
  impact: 30
  kill_chain_phases:
  - Installation
  message: An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ modifying SSH Authorized Keys.
  mitre_attack_id:
  - T1098.004
  nist:
  - DE.CM
  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 #parent process name
  - Processes.parent_process #parent cmdline
  - Processes.original_file_name
  - Processes.process_name #process name
  - Processes.process #process cmdline
  - Processes.process_id
  - Processes.parent_process_path
  - Processes.process_path
  - Processes.parent_process_id
  risk_score: 15
  security_domain: endpoint