detect_regasm_spawning_a_process.yml

name: Detect Regasm Spawning a Process
id: 72170ec5-f7d2-42f5-aefb-2b8be6aad15f
version: 1
date: '2021-02-12'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic identifies regasm.exe spawning a process. This
  particular technique has been used in the wild to bypass application control products.
  Regasm.exe and Regsvcs.exe are signed by Microsoft. Spawning of a child process
  is rare from either process and should be investigated further. During investigation,
  identify and retrieve the content being loaded. Review parallel processes for additional
  suspicious behavior. Gather any other file modifications and review accordingly.
  regsvcs.exe and regasm.exe are natively found in C:\Windows\Microsoft.NET\Framework\v*\regasm|regsvcs.exe
  and C:\Windows\Microsoft.NET\Framework64\v*\regasm|regsvcs.exe.
data_source:
- Sysmon Event ID 1
search:
  selection1:
    ParentImage: regasm.exe
  condition: selection1
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.
known_false_positives: Although unlikely, limited instances of regasm.exe or regsvcs.exe
  may cause a false positive. Filter based endpoint usage, command line arguments,
  or process lineage.
references:
- https://attack.mitre.org/techniques/T1218/009/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.009/T1218.009.md
- https://lolbas-project.github.io/lolbas/Binaries/Regsvcs/
- https://lolbas-project.github.io/lolbas/Binaries/Regasm/
tags:
  analytic_story:
  - Suspicious Regsvcs Regasm Activity
  - Living Off The Land
  asset_type: Endpoint
  confidence: 80
  impact: 80
  message: An instance of $parent_process_name$ spawning $process_name$ was identified
    on endpoint $dest$ by user $user$ spawning a child process, typically not normal
    behavior for $parent_process_name$.
  mitre_attack_id:
  - T1218
  - T1218.009
  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: 64
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.009/atomic_red_team/windows-sysmon.log
    source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
    sourcetype: xmlwineventlog