Detection: Windows Defender ASR Rule Disabled

Updated Date: 2024-08-15 ID: 429d611b-3183-49a7-b235-fc4203c4e1cb Author: Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies when a Windows Defender ASR rule disabled 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 rule disabled events that are generated when an ASR rule is disabled.

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| search New_Registry_Value="Disabled" 
 8| stats count min(_time) as firstTime max(_time) as lastTime by host, New_Value, Old_Value, Old_Registry_Value, New_Registry_Value, ASR_ID 
 9| lookup asr_rules ID AS ASR_ID OUTPUT ASR_Rule 
10| `security_content_ctime(firstTime)` 
11| `security_content_ctime(lastTime)`
12| rename host as dest 
13| `windows_defender_asr_rule_disabled_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

Name	Value
ms_defender	`source="WinEventLog:Microsoft-Windows-Windows Defender/Operational"`
windows_defender_asr_rule_disabled_filter	`search *`

windows_defender_asr_rule_disabled_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
T1112	Modify Registry	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT19

APT32

APT38

APT41

Blue Mockingbird

Dragonfly

Earth Lusca

Ember Bear

FIN8

Gamaredon Group

Gorgon Group

Kimsuky

LuminousMoth

Magic Hound

Patchwork

Silence

TA505

Threat Group-3390

Turla

Wizard Spider

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 Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

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 may occur if applications are typically disabling ASR rules in the environment. Monitor for changes to ASR rules to determine if this is a false positive.

Associated Analytic Story

Windows Attack Surface Reduction

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
ASR rule disabled event, $ASR_Rule$, was triggered on $dest$.	100	100	100

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

https://asrgen.streamlit.app/

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: 3