certutil_download_with_verifyctl_and_split_arguments.yml

name: CertUtil Download With VerifyCtl and Split Arguments
id: 801ad9e4-8bfb-11eb-8b31-acde48001122
version: 1
date: '2021-03-23'
author: Michael Haag, Splunk
type: batch
datamodel:
- Endpoint
description: 'Certutil.exe may download a file from a remote destination using `-VerifyCtl`.
  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.
  \ During triage, capture any files on disk and review. Review the reputation of
  the remote IP or domain in question. Using `-VerifyCtl`, the file will either be
  written to the current working directory or `%APPDATA%\..\LocalLow\Microsoft\CryptnetUrlCache\Content\<hash>`. '
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
  as lastTime from datamodel=Endpoint.Processes where Processes.process_name=certutil.exe
  Processes.process=*verifyctl* Processes.process=*split* by Processes.dest Processes.user
  Processes.parent_process 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)` | `certutil_download_with_verifyctl_and_split_arguments_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.
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.hexacorn.com/blog/2020/08/23/certutil-one-more-gui-lolbin/
- https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/cc732443(v=ws.11)#-verifyctl
- https://www.avira.com/en/blog/certutil-abused-by-attackers-to-spread-threats
tags:
  analytic_story:
  - Ingress Tool Transfer
  automated_detection_testing: passed
  dataset:
  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1105/atomic_red_team/windows-sysmon.log
  kill_chain_phases:
  - Exploitation
  mitre_attack_id:
  - T1105
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - Processes.process
  - Processes.parent_process
  - Processes.process_name
  - Processes.user
  - Processes.dest
  security_domain: endpoint