certutil_download_with_urlcache_and_split_arguments.yml

name: CertUtil Download With URLCache and Split Arguments
id: 415b4306-8bfb-11eb-85c4-acde48001122
version: 3
date: '2022-02-03'
author: Michael Haag, Splunk
status: production
type: TTP
description: Certutil.exe may download a file from a remote destination using `-urlcache`.
  This behavior does require a URL to be passed on the command-line. In addition,
  `-f` (force) and `-split` (Split embedded ASN.1 elements, and save to files) will
  be used. It is not entirely common for `certutil.exe` to contact public IP space.
  However, it is uncommon for `certutil.exe` to write files to world writeable paths.\
  During triage, capture any files on disk and review. Review the reputation of the
  remote IP or domain in question.
data_source:
- Sysmon Event ID 1
search:
  selection1:
    OriginalFileName: CertUtil.exe
  selection2:
    Image|endswith: certutil.exe
  selection3:
    CommandLine: '*split*'
  selection4:
    CommandLine: '*urlcache*'
  selection5:
    CommandLine: '*urlcache*'
  condition: (selection1 or selection2) and selection3 and selection4 or selection5
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: Limited false positives in most environments, however tune
  as needed based on parent-child relationship or network connection.
references:
- https://attack.mitre.org/techniques/T1105/
- https://www.avira.com/en/blog/certutil-abused-by-attackers-to-spread-threats
- https://web.archive.org/web/20210921110637/https://www.fireeye.com/blog/threat-research/2019/10/certutil-qualms-they-came-to-drop-fombs.html
tags:
  analytic_story:
  - Ingress Tool Transfer
  - DarkSide Ransomware
  - Living Off The Land
  - ProxyNotShell
  - CISA AA22-277A
  - Forest Blizzard
  - Flax Typhoon
  asset_type: Endpoint
  confidence: 100
  impact: 90
  message: An instance of $parent_process_name$ spawning $process_name$ was identified
    on endpoint $dest$ by user $user$ attempting to download a file.
  mitre_attack_id:
  - T1105
  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: 90
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1105/atomic_red_team/windows-sysmon.log
    source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
    sourcetype: xmlwineventlog