Detection: Windows Defender ASR Rules Stacking

Description

The following analytic identifies security events from Microsoft Defender, focusing on Exploit Guard and Attack Surface Reduction (ASR) features. It detects Event IDs 1121, 1126, 1131, and 1133 for blocked operations, and Event IDs 1122, 1125, 1132, and 1134 for audit logs. Event ID 1129 indicates user overrides, while Event ID 5007 signals configuration changes. This detection uses a lookup to correlate ASR rule GUIDs with descriptive names. Monitoring these events is crucial for identifying unauthorized operations, potential security breaches, and policy enforcement issues. If confirmed malicious, attackers could bypass security measures, execute unauthorized actions, or alter system configurations.

Search

1`ms_defender` EventCode IN (1121, 1122, 1125, 1126, 1129, 1131, 1132, 1133, 1134, 5007) 
2| stats count min(_time) as firstTime max(_time) as lastTime by host Parent_Commandline, Process_Name, Path, ID, EventCode 
3| lookup asr_rules ID OUTPUT ASR_Rule 
4| fillnull value=NULL 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)`
7| rename host as dest 
8| `windows_defender_asr_rules_stacking_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Defender 1121	Windows	'xmlwineventlog'	'WinEventLog:Microsoft-Windows-Windows Defender/Operational'
Windows Event Log Defender 1122	Windows	'xmlwineventlog'	'WinEventLog:Microsoft-Windows-Windows Defender/Operational'
Windows Event Log Defender 1129	Windows	'xmlwineventlog'	'WinEventLog:Microsoft-Windows-Windows Defender/Operational'
Windows Event Log Defender 5007	Windows	'xmlwineventlog'	'WinEventLog:Microsoft-Windows-Windows Defender/Operational'

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. Note that Audit and block Event IDs have different fields, therefore the analytic will need to be modified for each type of event. The analytic can be modified to look for specific ASR rules, or to look for specific Event IDs. EventID 5007 is a change in the registry, and may be a false positive. This can be removed from the search if desired.

Known False Positives

False positives are not expected with this analytic, since it is a hunting analytic. It is meant to show the use of ASR rules and how they can be used to detect malicious activity.

Associated Analytic Story

• Windows Attack Surface Reduction

References

• https://asrgen.streamlit.app/

• https://learn.microsoft.com/en-us/microsoft-365/security/defender-endpoint/attack-surface-reduction?view=o365-worldwide

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: 5