splunk-security_content/detections/endpoint/certutil_with_decode_argument.yml

name: CertUtil With Decode Argument
id: bfe94226-8c10-11eb-a4b3-acde48001122
version: 3
date: '2024-05-27'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic detects the use of CertUtil.exe with the 'decode'
  argument, which may indicate an attempt to decode a previously encoded file, potentially
  containing malicious payloads. This detection leverages data from Endpoint Detection
  and Response (EDR) agents, focusing on command-line executions involving CertUtil.exe.
  This activity is significant because attackers often use CertUtil to decode malicious
  files downloaded from the internet, which are then executed to compromise the system.
  If confirmed malicious, this activity could lead to unauthorized code execution,
  further system compromise, and potential data exfiltration.
data_source:
- Sysmon EventID 1
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
  as lastTime from datamodel=Endpoint.Processes where `process_certutil` Processes.process=*decode*
  by Processes.dest Processes.user Processes.parent_process 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)`
  | `certutil_with_decode_argument_filter`'
how_to_implement: The detection is based on data that originates from Endpoint Detection
  and Response (EDR) agents. These agents are designed to provide security-related
  telemetry from the endpoints where the agent is installed. To implement this search,
  you must ingest logs that contain the process GUID, process name, and parent process.
  Additionally, you must ingest complete command-line executions. These logs must
  be processed using the appropriate Splunk Technology Add-ons that are specific to
  the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint`
  data model. Use the Splunk Common Information Model (CIM) to normalize the field
  names and speed up the data modeling process.
known_false_positives: Typically seen used to `encode` files, but it is possible to
  see legitimate use of `decode`. Filter based on parent-child relationship, file
  paths, endpoint or user.
references:
- https://attack.mitre.org/techniques/T1140/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1140/T1140.md
- https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/certutil
- https://www.bleepingcomputer.com/news/security/certutilexe-could-allow-attackers-to-download-malware-while-bypassing-av/
tags:
  analytic_story:
  - Deobfuscate-Decode Files or Information
  - Living Off The Land
  - Forest Blizzard
  - APT29 Diplomatic Deceptions with WINELOADER
  group:
  - APT29
  - Cozy Bear
  - Midnight Blizzard
  asset_type: Endpoint
  confidence: 80
  impact: 50
  message: An instance of $parent_process_name$ spawning $process_name$ was identified
    on endpoint $dest$ by user $user$ attempting to decode a file.
  mitre_attack_id:
  - T1140
  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
  - Processes.parent_process
  - Processes.original_file_name
  - Processes.process_name
  - Processes.process
  - Processes.process_id
  - Processes.parent_process_path
  - Processes.process_path
  - Processes.parent_process_id
  risk_score: 40
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: 
      https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1140/atomic_red_team/windows-sysmon.log
    source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
    sourcetype: xmlwineventlog