Add DefaultUser And Password In Registry

name: Add DefaultUser And Password In Registry
id: d4a3eb62-0f1e-11ec-a971-acde48001122
version: 13
date: '2026-03-10'
author: Teoderick Contreras, Splunk, Steven Dick
status: production
type: Anomaly
description: The following analytic detects suspicious registry modifications that implement auto admin logon by adding DefaultUserName and DefaultPassword values. It leverages data from the Endpoint.Registry data model, specifically monitoring changes to the "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon" registry path. This activity is significant because it is associated with BlackMatter ransomware, which uses this technique to automatically log on to compromised hosts and continue encryption after a safe mode boot. If confirmed malicious, this could allow attackers to maintain persistence and further encrypt the network, leading to significant data loss and operational disruption.
data_source:
    - Sysmon EventID 12
    - Sysmon EventID 13
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Registry WHERE (Registry.registry_path= "*SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Winlogon*" AND Registry.registry_value_name= DefaultPassword OR Registry.registry_value_name= DefaultUserName) by Registry.action Registry.dest Registry.process_guid Registry.process_id Registry.registry_hive Registry.registry_path Registry.registry_key_name Registry.registry_value_data Registry.registry_value_name Registry.registry_value_type Registry.status Registry.user Registry.vendor_product | `drop_dm_object_name(Registry)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `add_defaultuser_and_password_in_registry_filter`'
how_to_implement: To successfully implement this search, you need to be ingesting logs with the registry value name, registry path, and registry value data from your endpoints. If you are using Sysmon, you must have at least version 2.0 of the official Sysmon TA. https://splunkbase.splunk.com/app/5709
known_false_positives: No false positives have been identified at this time.
references:
    - https://news.sophos.com/en-us/2021/08/09/blackmatter-ransomware-emerges-from-the-shadow-of-darkside/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") 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: modified registry key $registry_key_name$ with registry value $registry_value_name$ to prepare autoadminlogon
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects: []
tags:
    analytic_story:
        - BlackMatter Ransomware
    asset_type: Endpoint
    mitre_attack_id:
        - T1552.002
    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/T1552.002/autoadminlogon/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog