Windows Defender ASR Registry Modification

name: Windows Defender ASR Registry Modification
id: 6a1b6cbe-6612-44c3-92b9-1a1bd77412eb
version: 7
date: '2025-05-02'
author: Michael Haag, Splunk
status: production
type: Hunting
data_source:
    - Windows Event Log Defender 5007
description: The following analytic detects modifications to Windows Defender Attack Surface Reduction (ASR) registry settings. It leverages Windows Defender Operational logs, specifically EventCode 5007, to identify changes in ASR rules. This activity is significant because ASR rules are designed to block actions commonly used by malware to exploit systems. Unauthorized modifications to these settings could indicate an attempt to weaken system defenses. If confirmed malicious, this could allow an attacker to bypass security measures, leading to potential system compromise and data breaches.
search: '`ms_defender` EventCode IN (5007) | rex field=New_Value "0x(?<New_Registry_Value>\\d+)$" | rex field=Old_Value "0x(?<Old_Registry_Value>\\d+)$" | rex field=New_Value "Rules\\\\(?<ASR_ID>[A-Fa-f0-9\\-]+)\\s*=" | eval New_Registry_Value=case(New_Registry_Value=="0", "Disabled", New_Registry_Value=="1", "Block", New_Registry_Value=="2", "Audit", New_Registry_Value=="6", "Warn") | eval Old_Registry_Value=case(Old_Registry_Value=="0", "Disabled", Old_Registry_Value=="1", "Block", Old_Registry_Value=="2", "Audit", Old_Registry_Value=="6", "Warn") | stats count min(_time) as firstTime max(_time) as lastTime by host, New_Value, Old_Value, Old_Registry_Value, New_Registry_Value, ASR_ID | lookup asr_rules ID AS ASR_ID OUTPUT ASR_Rule | `security_content_ctime(firstTime)`| rename host as dest | `security_content_ctime(lastTime)` | `windows_defender_asr_registry_modification_filter`'
how_to_implement: The following analytic requires collection of Windows Defender Operational logs in either XML or multi-line. To collect, setup a new input for the Windows Defender Operational logs. In addition, it does require a lookup that maps the ID to ASR Rule name.
known_false_positives: False positives are expected from legitimate applications generating events that are similar to those generated by malicious activity. For example, Event ID 5007 is generated when a process attempts to modify a registry key that is related to ASR rules. This can be triggered by legitimate applications that attempt to modify registry keys that are not blocked by ASR rules.
references:
    - https://asrgen.streamlit.app/
tags:
    analytic_story:
        - Windows Attack Surface Reduction
    asset_type: Endpoint
    atomic_guid: []
    mitre_attack_id:
        - T1112
    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/T1059/defender/asr_registry.log
          source: WinEventLog:Microsoft-Windows-Windows Defender/Operational
          sourcetype: XmlWinEventLog