Detection: Windows Defender ASR Block Events

Updated Date: 2024-11-13 ID: 026f5f4e-e99f-4155-9e63-911ba587300b Author: Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This detection searches for Windows Defender ASR block events. ASR is a feature of Windows Defender Exploit Guard that prevents actions and apps that are typically used by exploit-seeking malware to infect machines. ASR rules are applied to processes and applications. When a process or application attempts to perform an action that is blocked by an ASR rule, an event is generated. This detection searches for ASR block events that are generated when a process or application attempts to perform an action that is blocked by an ASR rule. Typically, these will be enabled in block most after auditing and tuning the ASR rules themselves. Set to TTP once tuned.

1`ms_defender` EventCode IN (1121, 1126, 1129, 1131, 1133) 
2| stats count min(_time) as firstTime max(_time) as lastTime by host, Path, Parent_Commandline, Process_Name, 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_block_events_filter`

Data Source

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

Macros Used

Name Value
ms_defender source="WinEventLog:Microsoft-Windows-Windows Defender/Operational"
windows_defender_asr_block_events_filter search *
windows_defender_asr_block_events_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1059 Command and Scripting Interpreter Execution
T1566.001 Spearphishing Attachment Initial Access
T1566.002 Spearphishing Link Initial Access
Delivery
Installation
DE.AE
CIS 10

Default Configuration

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

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

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.

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 1122 is generated when a process attempts to load a DLL that is blocked by an ASR rule. This can be triggered by legitimate applications that attempt to load DLLs that are not blocked by ASR rules. This is block only.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

ASR block event, $ASR_Rule$, was triggered on $dest$.

Risk Object Risk Object Type Risk Score Threat Objects
dest system 45 No Threat Objects

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset WinEventLog:Microsoft-Windows-Windows Defender/Operational XmlWinEventLog
Integration ✅ Passing Dataset WinEventLog:Microsoft-Windows-Windows Defender/Operational XmlWinEventLog

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