Detection: Windows Defender ASR Registry Modification

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

 1`ms_defender` EventCode IN (5007) 
 2| rex field=New_Value "0x(?<New_Registry_Value>\\d+)$" 
 3| rex field=Old_Value "0x(?<Old_Registry_Value>\\d+)$" 
 4| rex field=New_Value "Rules\\\\(?<ASR_ID>[A-Fa-f0-9\\-]+)\\s*=" 
 5| 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") 
 6| 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") 
 7| stats count min(_time) as firstTime max(_time) as lastTime by host, New_Value, Old_Value, Old_Registry_Value, New_Registry_Value, ASR_ID 
 8| lookup asr_rules ID AS ASR_ID OUTPUT ASR_Rule 
 9| `security_content_ctime(firstTime)`
10| rename host as dest 
11| `security_content_ctime(lastTime)` 
12| `windows_defender_asr_registry_modification_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Windows Event Log Defender 5007	Windows	'xmlwineventlog'	'WinEventLog:Microsoft-Windows-Windows Defender/Operational'	N/A

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

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.

Associated Analytic Story

• Windows Attack Surface Reduction

Risk Based Analytics (RBA)

References

• https://asrgen.streamlit.app/

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 3