CertUtil Download With URLCache and Split Arguments

SPLUNK detection rule by Michael Haag, Splunk · Apache-2.0

This analytic has been deprecated in favor of "Windows CertUtil Download". The following analytic detects the use of certutil.exe to download files using the `-urlcache` and `-f` arguments. It leverages Endpoint Detection and Response (EDR) data, focusing on command-line executions that include these specific arguments. This activity is significant because certutil.exe is typically used for certificate services, and its use to download files from remote locations is uncommon and potentially malicious. If confirmed, this behavior could indicate an attempt to download and execute malicious payloads, leading to potential system compromise and unauthorized data access.

name: CertUtil Download With URLCache and Split Arguments
id: 415b4306-8bfb-11eb-85c4-acde48001122
version: 13
creation_date: '2021-03-24'
modification_date: '2026-05-13'
author: Michael Haag, Splunk
status: removed
type: TTP
description: This analytic has been deprecated in favor of "Windows CertUtil Download". The following analytic detects the use of certutil.exe to download files using the `-urlcache` and `-f` arguments. It leverages Endpoint Detection and Response (EDR) data, focusing on command-line executions that include these specific arguments. This activity is significant because certutil.exe is typically used for certificate services, and its use to download files from remote locations is uncommon and potentially malicious. If confirmed, this behavior could indicate an attempt to download and execute malicious payloads, leading to potential system compromise and unauthorized data access.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_certutil` Processes.process="*urlcache*" (Processes.process="*/f *" OR Processes.process="*-f *") by Processes.action Processes.dest Processes.original_file_name Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `certutil_download_with_urlcache_and_split_arguments_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: 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
    - https://lolbas-project.github.io/lolbas/Binaries/Certutil/
drilldown_searches:
    - name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ attempting to download a file.
    risk_objects:
        - field: user
          type: user
          score: 90
        - field: dest
          type: system
          score: 90
    threat_objects:
        - field: parent_process_name
          type: parent_process_name
        - field: process_name
          type: process_name
tags:
    analytic_story:
        - ProxyNotShell
        - Living Off The Land
        - DarkSide Ransomware
        - Forest Blizzard
        - Flax Typhoon
        - Ingress Tool Transfer
        - Compromised Windows Host
        - CISA AA22-277A
        - Storm-2460 CLFS Zero Day Exploitation
    asset_type: Endpoint
    mitre_attack_id:
        - T1105
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    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
deprecation_info:
    reason: Detection deprecated in favor of "Windows File Download Via CertUtil", in order to provide a better experience of the alert
    removed_in_version: 5.8.0
    replacement_content:
        - Windows File Download Via CertUtil

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